Delegate.CreateDelegate Method
Definition
Important
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Creates a delegate of the specified type.
Overloads
CreateDelegate(Type, Type, String, Boolean, Boolean) |
Creates a delegate of the specified type that represents the specified static method of the specified class, with the specified case-sensitivity and the specified behavior on failure to bind. |
CreateDelegate(Type, Type, String, Boolean) |
Creates a delegate of the specified type that represents the specified static method of the specified class, with the specified case-sensitivity. |
CreateDelegate(Type, Object, String, Boolean) |
Creates a delegate of the specified type that represents the specified instance method to invoke on the specified class instance with the specified case-sensitivity. |
CreateDelegate(Type, Object, MethodInfo, Boolean) |
Creates a delegate of the specified type that represents the specified static or instance method, with the specified first argument and the specified behavior on failure to bind. |
CreateDelegate(Type, Object, String, Boolean, Boolean) |
Creates a delegate of the specified type that represents the specified instance method to invoke on the specified class instance, with the specified case-sensitivity and the specified behavior on failure to bind. |
CreateDelegate(Type, MethodInfo, Boolean) |
Creates a delegate of the specified type to represent the specified static method, with the specified behavior on failure to bind. |
CreateDelegate(Type, Object, String) |
Creates a delegate of the specified type that represents the specified instance method to invoke on the specified class instance. |
CreateDelegate(Type, Object, MethodInfo) |
Creates a delegate of the specified type that represents the specified static or instance method, with the specified first argument. |
CreateDelegate(Type, Type, String) |
Creates a delegate of the specified type that represents the specified static method of the specified class. |
CreateDelegate(Type, MethodInfo) |
Creates a delegate of the specified type to represent the specified method. |
CreateDelegate(Type, Type, String, Boolean, Boolean)
Creates a delegate of the specified type that represents the specified static method of the specified class, with the specified case-sensitivity and the specified behavior on failure to bind.
public:
static Delegate ^ CreateDelegate(Type ^ type, Type ^ target, System::String ^ method, bool ignoreCase, bool throwOnBindFailure);
public static Delegate? CreateDelegate (Type type, Type target, string method, bool ignoreCase, bool throwOnBindFailure);
public static Delegate CreateDelegate (Type type, Type target, string method, bool ignoreCase, bool throwOnBindFailure);
static member CreateDelegate : Type * Type * string * bool * bool -> Delegate
Public Shared Function CreateDelegate (type As Type, target As Type, method As String, ignoreCase As Boolean, throwOnBindFailure As Boolean) As Delegate
Parameters
- method
- String
The name of the static method that the delegate is to represent.
- ignoreCase
- Boolean
A Boolean indicating whether to ignore the case when comparing the name of the method.
- throwOnBindFailure
- Boolean
true
to throw an exception if method
cannot be bound; otherwise, false
.
Returns
A delegate of the specified type that represents the specified static method of the specified class.
Exceptions
type
does not inherit MulticastDelegate.
-or-
type
is not a RuntimeType
. See Runtime Types in Reflection.
-or-
target
is not a RuntimeType
.
-or-
target
is an open generic type. That is, its ContainsGenericParameters property is true
.
-or-
method
is not a static
method (Shared
method in Visual Basic).
-or-
method
cannot be bound, for example because it cannot be found, and throwOnBindFailure
is true
.
The Invoke
method of type
is not found.
The caller does not have the permissions necessary to access method
.
Remarks
This method creates delegates for static methods only. An instance method is a method that is associated with an instance of a class; a static method is a method that is associated with the class itself.
Note
Starting with the .NET Framework 2.0 Service Pack 1, this method can be used to access non-public methods if the caller has been granted ReflectionPermission with the ReflectionPermissionFlag.RestrictedMemberAccess flag and if the grant set of the non-public methods is restricted to the caller's grant set, or a subset thereof. (See Security Considerations for Reflection.)
To use this functionality, your application should target the .NET Framework 3.5 or later.
See also
Applies to
CreateDelegate(Type, Type, String, Boolean)
Creates a delegate of the specified type that represents the specified static method of the specified class, with the specified case-sensitivity.
public:
static Delegate ^ CreateDelegate(Type ^ type, Type ^ target, System::String ^ method, bool ignoreCase);
public static Delegate CreateDelegate (Type type, Type target, string method, bool ignoreCase);
static member CreateDelegate : Type * Type * string * bool -> Delegate
Public Shared Function CreateDelegate (type As Type, target As Type, method As String, ignoreCase As Boolean) As Delegate
Parameters
- method
- String
The name of the static method that the delegate is to represent.
- ignoreCase
- Boolean
A Boolean indicating whether to ignore the case when comparing the name of the method.
Returns
A delegate of the specified type that represents the specified static method of the specified class.
Exceptions
type
does not inherit MulticastDelegate.
-or-
type
is not a RuntimeType
. See Runtime Types in Reflection.
-or-
target
is not a RuntimeType
.
-or-
target
is an open generic type. That is, its ContainsGenericParameters property is true
.
-or-
method
is not a static
method (Shared
method in Visual Basic).
-or-
method
cannot be bound, for example because it cannot be found.
The Invoke
method of type
is not found.
The caller does not have the permissions necessary to access method
.
Remarks
This method creates delegates for static methods only. An instance method is a method that is associated with an instance of a class; a static method is a method that is associated with the class itself.
This method overload is equivalent to calling the CreateDelegate(Type, Type, String, Boolean, Boolean) method overload, specifying true
for throwOnBindFailure
.
Note
Starting with the .NET Framework 2.0 Service Pack 1, this method can be used to access non-public methods if the caller has been granted ReflectionPermission with the ReflectionPermissionFlag.RestrictedMemberAccess flag and if the grant set of the non-public methods is restricted to the caller's grant set, or a subset thereof. (See Security Considerations for Reflection.)
To use this functionality, your application should target the .NET Framework 3.5 or later.
See also
Applies to
CreateDelegate(Type, Object, String, Boolean)
Creates a delegate of the specified type that represents the specified instance method to invoke on the specified class instance with the specified case-sensitivity.
public:
static Delegate ^ CreateDelegate(Type ^ type, System::Object ^ target, System::String ^ method, bool ignoreCase);
public static Delegate CreateDelegate (Type type, object target, string method, bool ignoreCase);
static member CreateDelegate : Type * obj * string * bool -> Delegate
Public Shared Function CreateDelegate (type As Type, target As Object, method As String, ignoreCase As Boolean) As Delegate
Parameters
- target
- Object
The class instance on which method
is invoked.
- method
- String
The name of the instance method that the delegate is to represent.
- ignoreCase
- Boolean
A Boolean indicating whether to ignore the case when comparing the name of the method.
Returns
A delegate of the specified type that represents the specified instance method to invoke on the specified class instance.
Exceptions
type
does not inherit MulticastDelegate.
-or-
type
is not a RuntimeType
. See Runtime Types in Reflection.
-or-
method
is not an instance method.
-or-
method
cannot be bound, for example because it cannot be found.
The Invoke
method of type
is not found.
The caller does not have the permissions necessary to access method
.
Remarks
This method creates delegates for instance methods only. An instance method is a method that is associated with an instance of a class; a static method is a method that is associated with the class itself.
This method overload is equivalent to calling the CreateDelegate(Type, Object, String, Boolean, Boolean) method overload, specifying true
for throwOnBindFailure
.
Note
Starting with the .NET Framework 2.0 Service Pack 1, this method can be used to access non-public methods if the caller has been granted ReflectionPermission with the ReflectionPermissionFlag.RestrictedMemberAccess flag and if the grant set of the non-public methods is restricted to the caller's grant set, or a subset thereof. (See Security Considerations for Reflection.)
To use this functionality, your application should target the .NET Framework 3.5 or later.
See also
Applies to
CreateDelegate(Type, Object, MethodInfo, Boolean)
Creates a delegate of the specified type that represents the specified static or instance method, with the specified first argument and the specified behavior on failure to bind.
public:
static Delegate ^ CreateDelegate(Type ^ type, System::Object ^ firstArgument, System::Reflection::MethodInfo ^ method, bool throwOnBindFailure);
public static Delegate? CreateDelegate (Type type, object? firstArgument, System.Reflection.MethodInfo method, bool throwOnBindFailure);
public static Delegate CreateDelegate (Type type, object firstArgument, System.Reflection.MethodInfo method, bool throwOnBindFailure);
static member CreateDelegate : Type * obj * System.Reflection.MethodInfo * bool -> Delegate
Public Shared Function CreateDelegate (type As Type, firstArgument As Object, method As MethodInfo, throwOnBindFailure As Boolean) As Delegate
Parameters
- firstArgument
- Object
An Object that is the first argument of the method the delegate represents. For instance methods, it must be compatible with the instance type.
- method
- MethodInfo
The MethodInfo describing the static or instance method the delegate is to represent.
- throwOnBindFailure
- Boolean
true
to throw an exception if method
cannot be bound; otherwise, false
.
Returns
A delegate of the specified type that represents the specified static or instance method, or null
if throwOnBindFailure
is false
and the delegate cannot be bound to method
.
Exceptions
type
does not inherit MulticastDelegate.
-or-
type
is not a RuntimeType
. See Runtime Types in Reflection.
-or-
method
cannot be bound, and throwOnBindFailure
is true
.
-or-
method
is not a RuntimeMethodInfo
. See Runtime Types in Reflection.
The Invoke
method of type
is not found.
The caller does not have the permissions necessary to access method
.
Examples
This section contains three code examples. The first example demonstrates the four kinds of delegates that can be created: closed over an instance method, open over an instance method, open over a static method, and closed over a static method.
The second code example demonstrates compatible parameter types and return types.
The third code example defines a single delegate type, and shows all the methods that delegate type can represent.
Example 1
The following code example demonstrates the four ways a delegate can be created using this overload of the CreateDelegate method.
Note
There are two overloads of the CreateDelegate method that specify firstArgument
and a MethodInfo; their functionality is the same except that one allows you to specify whether to throw on failure to bind, and the other always throws. This code example uses both overloads.
The example declares a class C
with a static method M2
and an instance method M1
, and three delegate types: D1
takes an instance of C
and a string, D2
takes a string, and D3
has no arguments.
A second class named Example
contains the code that creates the delegates.
A delegate of type
D2
, closed over an instance ofC
, is created for the instance methodM1
. It is invoked with different strings, to show that the bound instance ofC
is always used.A delegate of type
D1
, representing an open instance method, is created for the instance methodM1
. An instance must be passed when the delegate is invoked.A delegate of type
D2
, representing an open static method, is created for the static methodM2
.Finally, a delegate of type
D3
, closed over a string, is created for the static methodM2
. The method is invoked to show that it uses the bound string.
using System;
using System.Reflection;
using System.Security.Permissions;
// Declare three delegate types for demonstrating the combinations
// of static versus instance methods and open versus closed
// delegates.
//
public delegate void D1(C c, string s);
public delegate void D2(string s);
public delegate void D3();
// A sample class with an instance method and a static method.
//
public class C
{
private int id;
public C(int id) { this.id = id; }
public void M1(string s)
{
Console.WriteLine("Instance method M1 on C: id = {0}, s = {1}",
this.id, s);
}
public static void M2(string s)
{
Console.WriteLine("Static method M2 on C: s = {0}", s);
}
}
public class Example
{
public static void Main()
{
C c1 = new C(42);
// Get a MethodInfo for each method.
//
MethodInfo mi1 = typeof(C).GetMethod("M1",
BindingFlags.Public | BindingFlags.Instance);
MethodInfo mi2 = typeof(C).GetMethod("M2",
BindingFlags.Public | BindingFlags.Static);
D1 d1;
D2 d2;
D3 d3;
Console.WriteLine("\nAn instance method closed over C.");
// In this case, the delegate and the
// method must have the same list of argument types; use
// delegate type D2 with instance method M1.
//
Delegate test =
Delegate.CreateDelegate(typeof(D2), c1, mi1, false);
// Because false was specified for throwOnBindFailure
// in the call to CreateDelegate, the variable 'test'
// contains null if the method fails to bind (for
// example, if mi1 happened to represent a method of
// some class other than C).
//
if (test != null)
{
d2 = (D2) test;
// The same instance of C is used every time the
// delegate is invoked.
d2("Hello, World!");
d2("Hi, Mom!");
}
Console.WriteLine("\nAn open instance method.");
// In this case, the delegate has one more
// argument than the instance method; this argument comes
// at the beginning, and represents the hidden instance
// argument of the instance method. Use delegate type D1
// with instance method M1.
//
d1 = (D1) Delegate.CreateDelegate(typeof(D1), null, mi1);
// An instance of C must be passed in each time the
// delegate is invoked.
//
d1(c1, "Hello, World!");
d1(new C(5280), "Hi, Mom!");
Console.WriteLine("\nAn open static method.");
// In this case, the delegate and the method must
// have the same list of argument types; use delegate type
// D2 with static method M2.
//
d2 = (D2) Delegate.CreateDelegate(typeof(D2), null, mi2);
// No instances of C are involved, because this is a static
// method.
//
d2("Hello, World!");
d2("Hi, Mom!");
Console.WriteLine("\nA static method closed over the first argument (String).");
// The delegate must omit the first argument of the method.
// A string is passed as the firstArgument parameter, and
// the delegate is bound to this string. Use delegate type
// D3 with static method M2.
//
d3 = (D3) Delegate.CreateDelegate(typeof(D3),
"Hello, World!", mi2);
// Each time the delegate is invoked, the same string is
// used.
d3();
}
}
/* This code example produces the following output:
An instance method closed over C.
Instance method M1 on C: id = 42, s = Hello, World!
Instance method M1 on C: id = 42, s = Hi, Mom!
An open instance method.
Instance method M1 on C: id = 42, s = Hello, World!
Instance method M1 on C: id = 5280, s = Hi, Mom!
An open static method.
Static method M2 on C: s = Hello, World!
Static method M2 on C: s = Hi, Mom!
A static method closed over the first argument (String).
Static method M2 on C: s = Hello, World!
*/
open System
open System.Reflection
// A sample class with an instance method and a static method.
type C(id) =
member _.M1(s) =
printfn $"Instance method M1 on C: id = %i{id}, s = %s{s}"
static member M2(s) =
printfn $"Static method M2 on C: s = %s{s}"
// Declare three delegate types for demonstrating the combinations
// of static versus instance methods and open versus closed
// delegates.
type D1 = delegate of C * string -> unit
type D2 = delegate of string -> unit
type D3 = delegate of unit -> unit
let c1 = C 42
// Get a MethodInfo for each method.
//
let mi1 = typeof<C>.GetMethod("M1", BindingFlags.Public ||| BindingFlags.Instance)
let mi2 = typeof<C>.GetMethod("M2", BindingFlags.Public ||| BindingFlags.Static)
printfn "\nAn instance method closed over C."
// In this case, the delegate and the
// method must have the same list of argument types use
// delegate type D2 with instance method M1.
let test = Delegate.CreateDelegate(typeof<D2>, c1, mi1, false)
// Because false was specified for throwOnBindFailure
// in the call to CreateDelegate, the variable 'test'
// contains null if the method fails to bind (for
// example, if mi1 happened to represent a method of
// some class other than C).
if test <> null then
let d2 = test :?> D2
// The same instance of C is used every time the
// delegate is invoked.
d2.Invoke "Hello, World!"
d2.Invoke "Hi, Mom!"
printfn "\nAn open instance method."
// In this case, the delegate has one more
// argument than the instance method this argument comes
// at the beginning, and represents the hidden instance
// argument of the instance method. Use delegate type D1
// with instance method M1.
let d1 = Delegate.CreateDelegate(typeof<D1>, null, mi1) :?> D1
// An instance of C must be passed in each time the
// delegate is invoked.
d1.Invoke(c1, "Hello, World!")
d1.Invoke(C 5280, "Hi, Mom!")
printfn "\nAn open static method."
// In this case, the delegate and the method must
// have the same list of argument types use delegate type
// D2 with static method M2.
let d2 = Delegate.CreateDelegate(typeof<D2>, null, mi2) :?> D2
// No instances of C are involved, because this is a static
// method.
d2.Invoke "Hello, World!"
d2.Invoke "Hi, Mom!"
printfn "\nA static method closed over the first argument (String)."
// The delegate must omit the first argument of the method.
// A string is passed as the firstArgument parameter, and
// the delegate is bound to this string. Use delegate type
// D3 with static method M2.
let d3 = Delegate.CreateDelegate(typeof<D3>, "Hello, World!", mi2) :?> D3
// Each time the delegate is invoked, the same string is used.
d3.Invoke()
// This code example produces the following output:
// An instance method closed over C.
// Instance method M1 on C: id = 42, s = Hello, World!
// Instance method M1 on C: id = 42, s = Hi, Mom!
//
// An open instance method.
// Instance method M1 on C: id = 42, s = Hello, World!
// Instance method M1 on C: id = 5280, s = Hi, Mom!
//
// An open static method.
// Static method M2 on C: s = Hello, World!
// Static method M2 on C: s = Hi, Mom!
//
// A static method closed over the first argument (String).
// Static method M2 on C: s = Hello, World!
Imports System.Reflection
Imports System.Security.Permissions
' Declare three delegate types for demonstrating the combinations
' of Shared versus instance methods and open versus closed
' delegates.
'
Public Delegate Sub D1(ByVal c As C, ByVal s As String)
Public Delegate Sub D2(ByVal s As String)
Public Delegate Sub D3()
' A sample class with an instance method and a Shared method.
'
Public Class C
Private id As Integer
Public Sub New(ByVal id As Integer)
Me.id = id
End Sub
Public Sub M1(ByVal s As String)
Console.WriteLine("Instance method M1 on C: id = {0}, s = {1}", _
Me.id, s)
End Sub
Public Shared Sub M2(ByVal s As String)
Console.WriteLine("Shared method M2 on C: s = {0}", s)
End Sub
End Class
Public Class Example
Public Shared Sub Main()
Dim c1 As New C(42)
' Get a MethodInfo for each method.
'
Dim mi1 As MethodInfo = GetType(C).GetMethod("M1", _
BindingFlags.Public Or BindingFlags.Instance)
Dim mi2 As MethodInfo = GetType(C).GetMethod("M2", _
BindingFlags.Public Or BindingFlags.Static)
Dim d1 As D1
Dim d2 As D2
Dim d3 As D3
Console.WriteLine(vbLf & "An instance method closed over C.")
' In this case, the delegate and the
' method must have the same list of argument types; use
' delegate type D2 with instance method M1.
'
Dim test As [Delegate] = _
[Delegate].CreateDelegate(GetType(D2), c1, mi1, False)
' Because False was specified for throwOnBindFailure
' in the call to CreateDelegate, the variable 'test'
' contains Nothing if the method fails to bind (for
' example, if mi1 happened to represent a method of
' some class other than C).
'
If test IsNot Nothing Then
d2 = CType(test, D2)
' The same instance of C is used every time the
' delegate is invoked.
d2("Hello, World!")
d2("Hi, Mom!")
End If
Console.WriteLine(vbLf & "An open instance method.")
' In this case, the delegate has one more
' argument than the instance method; this argument comes
' at the beginning, and represents the hidden instance
' argument of the instance method. Use delegate type D1
' with instance method M1.
'
d1 = CType([Delegate].CreateDelegate(GetType(D1), Nothing, mi1), D1)
' An instance of C must be passed in each time the
' delegate is invoked.
'
d1(c1, "Hello, World!")
d1(New C(5280), "Hi, Mom!")
Console.WriteLine(vbLf & "An open Shared method.")
' In this case, the delegate and the method must
' have the same list of argument types; use delegate type
' D2 with Shared method M2.
'
d2 = CType([Delegate].CreateDelegate(GetType(D2), Nothing, mi2), D2)
' No instances of C are involved, because this is a Shared
' method.
'
d2("Hello, World!")
d2("Hi, Mom!")
Console.WriteLine(vbLf & "A Shared method closed over the first argument (String).")
' The delegate must omit the first argument of the method.
' A string is passed as the firstArgument parameter, and
' the delegate is bound to this string. Use delegate type
' D3 with Shared method M2.
'
d3 = CType([Delegate].CreateDelegate(GetType(D3), "Hello, World!", mi2), D3)
' Each time the delegate is invoked, the same string is
' used.
d3()
End Sub
End Class
' This code example produces the following output:
'
'An instance method closed over C.
'Instance method M1 on C: id = 42, s = Hello, World!
'Instance method M1 on C: id = 42, s = Hi, Mom!
'
'An open instance method.
'Instance method M1 on C: id = 42, s = Hello, World!
'Instance method M1 on C: id = 5280, s = Hi, Mom!
'
'An open Shared method.
'Shared method M2 on C: s = Hello, World!
'Shared method M2 on C: s = Hi, Mom!
'
'A Shared method closed over the first argument (String).
'Shared method M2 on C: s = Hello, World!
'
Example 2
The following code example demonstrates compatibility of parameter types and return types.
Note
This code example uses the CreateDelegate(Type, MethodInfo) method overload. The use of other overloads that take MethodInfo is similar.
The code example defines a base class named Base
and a class named Derived
that derives from Base
. The derived class has a static
(Shared
in Visual Basic) method named MyMethod
with one parameter of type Base
and a return type of Derived
. The code example also defines a delegate named Example
that has one parameter of type Derived
and a return type of Base
.
The code example demonstrates that the delegate named Example
can be used to represent the method MyMethod
. The method can be bound to the delegate because:
The parameter type of the delegate (
Derived
) is more restrictive than the parameter type ofMyMethod
(Base
), so that it is always safe to pass the argument of the delegate toMyMethod
.The return type of
MyMethod
(Derived
) is more restrictive than the parameter type of the delegate (Base
), so that it is always safe to cast the return type of the method to the return type of the delegate.
The code example produces no output.
using namespace System;
using namespace System::Reflection;
// Define two classes to use in the demonstration, a base class and
// a class that derives from it.
//
public ref class Base {};
public ref class Derived : Base
{
// Define a static method to use in the demonstration. The method
// takes an instance of Base and returns an instance of Derived.
// For the purposes of the demonstration, it is not necessary for
// the method to do anything useful.
//
public:
static Derived^ MyMethod(Base^ arg)
{
Base^ dummy = arg;
return gcnew Derived();
}
};
// Define a delegate that takes an instance of Derived and returns an
// instance of Base.
//
public delegate Base^ Example(Derived^ arg);
void main()
{
// The binding flags needed to retrieve MyMethod.
BindingFlags flags = BindingFlags::Public | BindingFlags::Static;
// Get a MethodInfo that represents MyMethod.
MethodInfo^ minfo = Derived::typeid->GetMethod("MyMethod", flags);
// Demonstrate contravariance of parameter types and covariance
// of return types by using the delegate Example to represent
// MyMethod. The delegate binds to the method because the
// parameter of the delegate is more restrictive than the
// parameter of the method (that is, the delegate accepts an
// instance of Derived, which can always be safely passed to
// a parameter of type Base), and the return type of MyMethod
// is more restrictive than the return type of Example (that
// is, the method returns an instance of Derived, which can
// always be safely cast to type Base).
//
Example^ ex =
(Example^) Delegate::CreateDelegate(Example::typeid, minfo);
// Execute MyMethod using the delegate Example.
//
Base^ b = ex(gcnew Derived());
}
using System;
using System.Reflection;
// Define two classes to use in the demonstration, a base class and
// a class that derives from it.
//
public class Base {}
public class Derived : Base
{
// Define a static method to use in the demonstration. The method
// takes an instance of Base and returns an instance of Derived.
// For the purposes of the demonstration, it is not necessary for
// the method to do anything useful.
//
public static Derived MyMethod(Base arg)
{
Base dummy = arg;
return new Derived();
}
}
// Define a delegate that takes an instance of Derived and returns an
// instance of Base.
//
public delegate Base Example(Derived arg);
class Test
{
public static void Main()
{
// The binding flags needed to retrieve MyMethod.
BindingFlags flags = BindingFlags.Public | BindingFlags.Static;
// Get a MethodInfo that represents MyMethod.
MethodInfo minfo = typeof(Derived).GetMethod("MyMethod", flags);
// Demonstrate contravariance of parameter types and covariance
// of return types by using the delegate Example to represent
// MyMethod. The delegate binds to the method because the
// parameter of the delegate is more restrictive than the
// parameter of the method (that is, the delegate accepts an
// instance of Derived, which can always be safely passed to
// a parameter of type Base), and the return type of MyMethod
// is more restrictive than the return type of Example (that
// is, the method returns an instance of Derived, which can
// always be safely cast to type Base).
//
Example ex =
(Example) Delegate.CreateDelegate(typeof(Example), minfo);
// Execute MyMethod using the delegate Example.
//
Base b = ex(new Derived());
}
}
open System
open System.Reflection
// Define two classes to use in the demonstration, a base class and
// a class that derives from it.
type Base() = class end
type Derived() =
inherit Base()
// Define a static method to use in the demonstration. The method
// takes an instance of Base and returns an instance of Derived.
// For the purposes of the demonstration, it is not necessary for
// the method to do anything useful.
static member MyMethod(arg: Base) =
Derived()
// Define a delegate that takes an instance of Derived and returns an
// instance of Base.
type Example = delegate of Derived -> Base
// The binding flags needed to retrieve MyMethod.
let flags = BindingFlags.Public ||| BindingFlags.Static
// Get a MethodInfo that represents MyMethod.
let minfo = typeof<Derived>.GetMethod("MyMethod", flags)
// Demonstrate contravariance of parameter types and covariance
// of return types by using the delegate Example to represent
// MyMethod. The delegate binds to the method because the
// parameter of the delegate is more restrictive than the
// parameter of the method (that is, the delegate accepts an
// instance of Derived, which can always be safely passed to
// a parameter of type Base), and the return type of MyMethod
// is more restrictive than the return type of Example (that
// is, the method returns an instance of Derived, which can
// always be safely cast to type Base).
let ex = Delegate.CreateDelegate(typeof<Example>, minfo) :?> Example
// Execute MyMethod using the delegate Example.
let b = Derived() |> ex.Invoke
Imports System.Reflection
' Define two classes to use in the demonstration, a base class and
' a class that derives from it.
'
Public Class Base
End Class
Public Class Derived
Inherits Base
' Define a Shared method to use in the demonstration. The method
' takes an instance of Base and returns an instance of Derived.
' For the purposes of the demonstration, it is not necessary for
' the method to do anything useful.
'
Public Shared Function MyMethod(ByVal arg As Base) As Derived
Dim dummy As Base = arg
Return New Derived()
End Function
End Class
' Define a delegate that takes an instance of Derived and returns an
' instance of Base.
'
Public Delegate Function Example(ByVal arg As Derived) As Base
Module Test
Sub Main()
' The binding flags needed to retrieve MyMethod.
Dim flags As BindingFlags = _
BindingFlags.Public Or BindingFlags.Static
' Get a MethodInfo that represents MyMethod.
Dim minfo As MethodInfo = _
GetType(Derived).GetMethod("MyMethod", flags)
' Demonstrate contravariance of parameter types and covariance
' of return types by using the delegate Example to represent
' MyMethod. The delegate binds to the method because the
' parameter of the delegate is more restrictive than the
' parameter of the method (that is, the delegate accepts an
' instance of Derived, which can always be safely passed to
' a parameter of type Base), and the return type of MyMethod
' is more restrictive than the return type of Example (that
' is, the method returns an instance of Derived, which can
' always be safely cast to type Base).
'
Dim ex As Example = CType( _
[Delegate].CreateDelegate(GetType(Example), minfo), _
Example _
)
' Execute MyMethod using the delegate Example.
'
Dim b As Base = ex(New Derived())
End Sub
End Module
Example 3
The following code example shows all the methods a single delegate type can represent.
Note
There are two overloads of the CreateDelegate method that specify firstArgument
and a MethodInfo; their functionality is the same except that one allows you to specify whether to throw on failure to bind, and the other always throws. This code example uses both overloads.
The code example defines two classes, C
and F
, and a delegate type D
with one argument of type C
. The classes have matching static and instance methods M1
, M3
, and M4
, and class C
also has an instance method M2
that has no arguments.
A third class named Example
contains the code that creates the delegates.
Delegates are created for instance method
M1
of typeC
and typeF
; each is closed over an instance of the respective type. MethodM1
of typeC
displays theID
properties of the bound instance and of the argument.A delegate is created for method
M2
of typeC
. This is an open instance delegate, in which the argument of the delegate represents the hidden first argument on the instance method. The method has no other arguments.Delegates are created for static method
M3
of typeC
and typeF
; these are open static delegates.Finally, delegates are created for static method
M4
of typeC
and typeF
; each method has the declaring type as its first argument, and an instance of the type is supplied, so the delegates are closed over their first arguments. MethodM4
of typeC
displays theID
properties of the bound instance and of the argument.
using System;
using System.Reflection;
using System.Security.Permissions;
// Declare a delegate type. The object of this code example
// is to show all the methods this delegate can bind to.
//
public delegate void D(C c);
// Declare two sample classes, C and F. Class C has an ID
// property so instances can be identified.
//
public class C
{
private int id;
public int ID { get { return id; }}
public C(int id) { this.id = id; }
public void M1(C c)
{
Console.WriteLine("Instance method M1(C c) on C: this.id = {0}, c.ID = {1}",
this.id, c.ID);
}
public void M2()
{
Console.WriteLine("Instance method M2() on C: this.id = {0}",
this.id);
}
public static void M3(C c)
{
Console.WriteLine("Static method M3(C c) on C: c.ID = {0}", c.ID);
}
public static void M4(C c1, C c2)
{
Console.WriteLine("Static method M4(C c1, C c2) on C: c1.ID = {0}, c2.ID = {1}",
c1.ID, c2.ID);
}
}
public class F
{
public void M1(C c)
{
Console.WriteLine("Instance method M1(C c) on F: c.ID = {0}",
c.ID);
}
public static void M3(C c)
{
Console.WriteLine("Static method M3(C c) on F: c.ID = {0}", c.ID);
}
public static void M4(F f, C c)
{
Console.WriteLine("Static method M4(F f, C c) on F: c.ID = {0}",
c.ID);
}
}
public class Example
{
public static void Main()
{
C c1 = new C(42);
C c2 = new C(1491);
F f1 = new F();
D d;
// Instance method with one argument of type C.
MethodInfo cmi1 = typeof(C).GetMethod("M1");
// Instance method with no arguments.
MethodInfo cmi2 = typeof(C).GetMethod("M2");
// Static method with one argument of type C.
MethodInfo cmi3 = typeof(C).GetMethod("M3");
// Static method with two arguments of type C.
MethodInfo cmi4 = typeof(C).GetMethod("M4");
// Instance method with one argument of type C.
MethodInfo fmi1 = typeof(F).GetMethod("M1");
// Static method with one argument of type C.
MethodInfo fmi3 = typeof(F).GetMethod("M3");
// Static method with an argument of type F and an argument
// of type C.
MethodInfo fmi4 = typeof(F).GetMethod("M4");
Console.WriteLine("\nAn instance method on any type, with an argument of type C.");
// D can represent any instance method that exactly matches its
// signature. Methods on C and F are shown here.
//
d = (D) Delegate.CreateDelegate(typeof(D), c1, cmi1);
d(c2);
d = (D) Delegate.CreateDelegate(typeof(D), f1, fmi1);
d(c2);
Console.WriteLine("\nAn instance method on C with no arguments.");
// D can represent an instance method on C that has no arguments;
// in this case, the argument of D represents the hidden first
// argument of any instance method. The delegate acts like a
// static method, and an instance of C must be passed each time
// it is invoked.
//
d = (D) Delegate.CreateDelegate(typeof(D), null, cmi2);
d(c1);
Console.WriteLine("\nA static method on any type, with an argument of type C.");
// D can represent any static method with the same signature.
// Methods on F and C are shown here.
//
d = (D) Delegate.CreateDelegate(typeof(D), null, cmi3);
d(c1);
d = (D) Delegate.CreateDelegate(typeof(D), null, fmi3);
d(c1);
Console.WriteLine("\nA static method on any type, with an argument of");
Console.WriteLine(" that type and an argument of type C.");
// D can represent any static method with one argument of the
// type the method belongs and a second argument of type C.
// In this case, the method is closed over the instance of
// supplied for the its first argument, and acts like an instance
// method. Methods on F and C are shown here.
//
d = (D) Delegate.CreateDelegate(typeof(D), c1, cmi4);
d(c2);
Delegate test =
Delegate.CreateDelegate(typeof(D), f1, fmi4, false);
// This final example specifies false for throwOnBindFailure
// in the call to CreateDelegate, so the variable 'test'
// contains Nothing if the method fails to bind (for
// example, if fmi4 happened to represent a method of
// some class other than F).
//
if (test != null)
{
d = (D) test;
d(c2);
}
}
}
/* This code example produces the following output:
An instance method on any type, with an argument of type C.
Instance method M1(C c) on C: this.id = 42, c.ID = 1491
Instance method M1(C c) on F: c.ID = 1491
An instance method on C with no arguments.
Instance method M2() on C: this.id = 42
A static method on any type, with an argument of type C.
Static method M3(C c) on C: c.ID = 42
Static method M3(C c) on F: c.ID = 42
A static method on any type, with an argument of
that type and an argument of type C.
Static method M4(C c1, C c2) on C: c1.ID = 42, c2.ID = 1491
Static method M4(F f, C c) on F: c.ID = 1491
*/
open System
// Declare two sample classes, C and F. Class C has an ID
// property so instances can be identified.
type C(id) =
member _.ID = id
member _.M1(c: C) =
printfn $"Instance method M1(C c) on C: this.id = {id}, c.ID = {c.ID}"
member _.M2() =
printfn $"Instance method M2() on C: this.id = {id}"
static member M3(c: C) =
printfn $"Static method M3(C c) on C: c.ID = {c.ID}"
static member M4(c1: C, c2: C) =
printfn $"Static method M4(C c1, C c2) on C: c1.ID = {c1.ID}, c2.ID = {c2.ID}"
// Declare a delegate type. The object of this code example
// is to show all the methods this delegate can bind to.
type D = delegate of C -> unit
type F() =
member _.M1(c: C) =
printfn $"Instance method M1(C c) on F: c.ID = {c.ID}"
member _.M3(c: C) =
printfn $"Static method M3(C c) on F: c.ID = {c.ID}"
member _.M4(f: F, c: C) =
printfn $"Static method M4(F f, C c) on F: c.ID = {c.ID}"
[<EntryPoint>]
let main _ =
let c1 = C 42
let c2 = C 1491
let f1 = F()
// Instance method with one argument of type C.
let cmi1 = typeof<C>.GetMethod "M1"
// Instance method with no arguments.
let cmi2 = typeof<C>.GetMethod "M2"
// Static method with one argument of type C.
let cmi3 = typeof<C>.GetMethod "M3"
// Static method with two arguments of type C.
let cmi4 = typeof<C>.GetMethod "M4"
// Instance method with one argument of type C.
let fmi1 = typeof<F>.GetMethod "M1"
// Static method with one argument of type C.
let fmi3 = typeof<F>.GetMethod "M3"
// Static method with an argument of type F and an argument
// of type C.
let fmi4 = typeof<F>.GetMethod "M4"
printfn "\nAn instance method on any type, with an argument of type C."
// D can represent any instance method that exactly matches its
// signature. Methods on C and F are shown here.
let d = Delegate.CreateDelegate(typeof<D>, c1, cmi1) :?> D
d.Invoke c2
let d = Delegate.CreateDelegate(typeof<D>, f1, fmi1) :?> D
d.Invoke c2
Console.WriteLine("\nAn instance method on C with no arguments.")
// D can represent an instance method on C that has no arguments
// in this case, the argument of D represents the hidden first
// argument of any instance method. The delegate acts like a
// static method, and an instance of C must be passed each time
// it is invoked.
let d = Delegate.CreateDelegate(typeof<D>, null, cmi2) :?> D
d.Invoke c1
printfn "\nA static method on any type, with an argument of type C."
// D can represent any static method with the same signature.
// Methods on F and C are shown here.
let d = Delegate.CreateDelegate(typeof<D>, null, cmi3) :?> D
d.Invoke c1
let d = Delegate.CreateDelegate(typeof<D>, null, fmi3) :?> D
d.Invoke c1
printfn "\nA static method on any type, with an argument of"
printfn " that type and an argument of type C."
// D can represent any static method with one argument of the
// type the method belongs and a second argument of type C.
// In this case, the method is closed over the instance of
// supplied for the its first argument, and acts like an instance
// method. Methods on F and C are shown here.
let d = Delegate.CreateDelegate(typeof<D>, c1, cmi4) :?> D
d.Invoke c2
let test =
Delegate.CreateDelegate(typeof<D>, f1, fmi4, false)
// This final example specifies false for throwOnBindFailure
// in the call to CreateDelegate, so the variable 'test'
// contains Nothing if the method fails to bind (for
// example, if fmi4 happened to represent a method of
// some class other than F).
match test with
| :? D as d ->
d.Invoke c2
| _ -> ()
0
// This code example produces the following output:
// An instance method on any type, with an argument of type C.
// Instance method M1(C c) on C: this.id = 42, c.ID = 1491
// Instance method M1(C c) on F: c.ID = 1491
//
// An instance method on C with no arguments.
// Instance method M2() on C: this.id = 42
//
// A static method on any type, with an argument of type C.
// Static method M3(C c) on C: c.ID = 42
// Static method M3(C c) on F: c.ID = 42
//
// A static method on any type, with an argument of
// that type and an argument of type C.
// Static method M4(C c1, C c2) on C: c1.ID = 42, c2.ID = 1491
// Static method M4(F f, C c) on F: c.ID = 1491
Imports System.Reflection
Imports System.Security.Permissions
' Declare a delegate type. The object of this code example
' is to show all the methods this delegate can bind to.
'
Public Delegate Sub D(ByVal c As C)
' Declare two sample classes, C and F. Class C has an ID
' property so instances can be identified.
'
Public Class C
Private _id As Integer
Public ReadOnly Property ID() As Integer
Get
Return _id
End Get
End Property
Public Sub New(ByVal newId As Integer)
Me._id = newId
End Sub
Public Sub M1(ByVal c As C)
Console.WriteLine("Instance method M1(c As C) on C: this.id = {0}, c.ID = {1}", _
Me.id, c.ID)
End Sub
Public Sub M2()
Console.WriteLine("Instance method M2() on C: this.id = {0}", Me.id)
End Sub
Public Shared Sub M3(ByVal c As C)
Console.WriteLine("Shared method M3(c As C) on C: c.ID = {0}", c.ID)
End Sub
Public Shared Sub M4(ByVal c1 As C, ByVal c2 As C)
Console.WriteLine("Shared method M4(c1 As C, c2 As C) on C: c1.ID = {0}, c2.ID = {1}", _
c1.ID, c2.ID)
End Sub
End Class
Public Class F
Public Sub M1(ByVal c As C)
Console.WriteLine("Instance method M1(c As C) on F: c.ID = {0}", c.ID)
End Sub
Public Shared Sub M3(ByVal c As C)
Console.WriteLine("Shared method M3(c As C) on F: c.ID = {0}", c.ID)
End Sub
Public Shared Sub M4(ByVal f As F, ByVal c As C)
Console.WriteLine("Shared method M4(f As F, c As C) on F: c.ID = {0}", c.ID)
End Sub
End Class
Public Class Example
Public Shared Sub Main()
Dim c1 As New C(42)
Dim c2 As New C(1491)
Dim f1 As New F()
Dim d As D
' Instance method with one argument of type C.
Dim cmi1 As MethodInfo = GetType(C).GetMethod("M1")
' Instance method with no arguments.
Dim cmi2 As MethodInfo = GetType(C).GetMethod("M2")
' Shared method with one argument of type C.
Dim cmi3 As MethodInfo = GetType(C).GetMethod("M3")
' Shared method with two arguments of type C.
Dim cmi4 As MethodInfo = GetType(C).GetMethod("M4")
' Instance method with one argument of type C.
Dim fmi1 As MethodInfo = GetType(F).GetMethod("M1")
' Shared method with one argument of type C.
Dim fmi3 As MethodInfo = GetType(F).GetMethod("M3")
' Shared method with an argument of type F and an
' argument of type C.
Dim fmi4 As MethodInfo = GetType(F).GetMethod("M4")
Console.WriteLine(vbLf & "An instance method on any type, with an argument of type C.")
' D can represent any instance method that exactly matches its
' signature. Methods on C and F are shown here.
'
d = CType([Delegate].CreateDelegate(GetType(D), c1, cmi1), D)
d(c2)
d = CType([Delegate].CreateDelegate(GetType(D), f1, fmi1), D)
d(c2)
Console.WriteLine(vbLf & "An instance method on C with no arguments.")
' D can represent an instance method on C that has no arguments;
' in this case, the argument of D represents the hidden first
' argument of any instance method. The delegate acts like a
' Shared method, and an instance of C must be passed each time
' it is invoked.
'
d = CType([Delegate].CreateDelegate(GetType(D), Nothing, cmi2), D)
d(c1)
Console.WriteLine(vbLf & "A Shared method on any type, with an argument of type C.")
' D can represent any Shared method with the same signature.
' Methods on F and C are shown here.
'
d = CType([Delegate].CreateDelegate(GetType(D), Nothing, cmi3), D)
d(c1)
d = CType([Delegate].CreateDelegate(GetType(D), Nothing, fmi3), D)
d(c1)
Console.WriteLine(vbLf & "A Shared method on any type, with an argument of")
Console.WriteLine(" that type and an argument of type C.")
' D can represent any Shared method with one argument of the
' type the method belongs and a second argument of type C.
' In this case, the method is closed over the instance of
' supplied for the its first argument, and acts like an instance
' method. Methods on F and C are shown here.
'
d = CType([Delegate].CreateDelegate(GetType(D), c1, cmi4), D)
d(c2)
Dim test As [Delegate] = _
[Delegate].CreateDelegate(GetType(D), f1, fmi4, false)
' This final example specifies False for throwOnBindFailure
' in the call to CreateDelegate, so the variable 'test'
' contains Nothing if the method fails to bind (for
' example, if fmi4 happened to represent a method of
' some class other than F).
'
If test IsNot Nothing Then
d = CType(test, D)
d(c2)
End If
End Sub
End Class
' This code example produces the following output:
'
'An instance method on any type, with an argument of type C.
'Instance method M1(c As C) on C: this.id = 42, c.ID = 1491
'Instance method M1(c As C) on F: c.ID = 1491
'
'An instance method on C with no arguments.
'Instance method M2() on C: this.id = 42
'
'A Shared method on any type, with an argument of type C.
'Shared method M3(c As C) on C: c.ID = 42
'Shared method M3(c As C) on F: c.ID = 42
'
'A Shared method on any type, with an argument of
' that type and an argument of type C.
'Shared method M4(c1 As C, c2 As C) on C: c1.ID = 42, c2.ID = 1491
'Shared method M4(f As F, c As C) on F: c.ID = 1491
'
Remarks
This method overload and the CreateDelegate(Type, Object, MethodInfo) method overload, which always throws on failure to bind, provide the most flexible way to create delegates. You can use them to create delegates for either static or instance methods, with or without a first argument.
Note
If you do not supply a first argument, use the CreateDelegate(Type, MethodInfo, Boolean) method overload for better performance.
The delegate type and the method must have compatible return types. That is, the return type of method
must be assignable to the return type of type
.
If firstArgument
is supplied, it is passed to method
every time the delegate is invoked; firstArgument
is said to be bound to the delegate, and the delegate is said to be closed over its first argument. If method
is static
(Shared
in Visual Basic), the argument list supplied when invoking the delegate includes all parameters except the first; if method
is an instance method, then firstArgument
is passed to the hidden instance parameter (represented by this
in C#, or by Me
in Visual Basic).
If firstArgument
is supplied, the first parameter of method
must be a reference type, and firstArgument
must be compatible with that type.
Important
If method
is static
(Shared
in Visual Basic) and its first parameter is of type Object or ValueType, then firstArgument
can be a value type. In this case firstArgument
is automatically boxed. Automatic boxing does not occur for any other arguments, as it would in a C# or Visual Basic function call.
If firstArgument
is a null reference and method
is an instance method, the result depends on the signatures of the delegate type type
and of method
:
If the signature of
type
explicitly includes the hidden first parameter ofmethod
, the delegate is said to represent an open instance method. When the delegate is invoked, the first argument in the argument list is passed to the hidden instance parameter ofmethod
.If the signatures of
method
andtype
match (that is, all parameter types are compatible), then the delegate is said to be closed over a null reference. Invoking the delegate is like calling an instance method on a null instance, which is not a particularly useful thing to do.
If firstArgument
is a null reference and method
is static, the result depends on the signatures of the delegate type type
and of method
:
If the signature of
method
andtype
match (that is, all parameter types are compatible), the delegate is said to represent an open static method. This is the most common case for static methods. In this case, you can get slightly better performance by using the CreateDelegate(Type, MethodInfo, Boolean) method overload.If the signature of
type
begins with the second parameter ofmethod
and the rest of the parameter types are compatible, then the delegate is said to be closed over a null reference. When the delegate is invoked, a null reference is passed to the first parameter ofmethod
.
Note
Starting with the .NET Framework 2.0 Service Pack 1, this method can be used to access non-public methods if the caller has been granted ReflectionPermission with the ReflectionPermissionFlag.RestrictedMemberAccess flag and if the grant set of the non-public methods is restricted to the caller's grant set, or a subset thereof. (See Security Considerations for Reflection.)
To use this functionality, your application should target the .NET Framework 3.5 or later.
Compatible Parameter Types and Return Type
The parameter types and return type of a delegate must be compatible with the parameter types and return type of the method the delegate represents; the types do not have to match exactly.
A parameter of a delegate is compatible with the corresponding parameter of a method if the type of the delegate parameter is more restrictive than the type of the method parameter, because this guarantees that an argument passed to the delegate can be passed safely to the method.
Similarly, the return type of a delegate is compatible with the return type of a method if the return type of the method is more restrictive than the return type of the delegate, because this guarantees that the return value of the method can be cast safely to the return type of the delegate.
For example, a delegate with a parameter of type Hashtable and a return type of Object can represent a method with a parameter of type Object and a return value of type Hashtable.
Determining the Methods a Delegate Can Represent
Another useful way to think of the flexibility provided by this overload of CreateDelegate is that any given delegate can represent four different combinations of method signature and method kind (static versus instance). Consider a delegate type D
with one argument of type C
. The following describes the methods D
can represent, ignoring the return type since it must match in all cases:
D
can represent any instance method that has exactly one argument of typeC
, regardless of what type the instance method belongs to. When CreateDelegate is called,firstArgument
is an instance of the typemethod
belongs to, and the resulting delegate is said to be closed over that instance. (Trivially,D
can also be closed over a null reference iffirstArgument
isnull
.)D
can represent an instance method ofC
that has no arguments. When CreateDelegate is called,firstArgument
is a null reference. The resulting delegate represents an open instance method, and an instance ofC
must be supplied each time it is invoked.D
can represent a static method that takes one argument of typeC
, and that method can belong to any type. When CreateDelegate is called,firstArgument
is a null reference. The resulting delegate represents an open static method, and an instance ofC
must be supplied each time it is invoked.D
can represent a static method that belongs to typeF
and has two arguments, of typeF
and typeC
. When CreateDelegate is called,firstArgument
is an instance ofF
. The resulting delegate represents a static method that is closed over that instance ofF
. Note that in the case whereF
andC
are the same type, the static method has two arguments of that type. (In this case,D
is closed over a null reference iffirstArgument
isnull
.)
See also
Applies to
CreateDelegate(Type, Object, String, Boolean, Boolean)
Creates a delegate of the specified type that represents the specified instance method to invoke on the specified class instance, with the specified case-sensitivity and the specified behavior on failure to bind.
public:
static Delegate ^ CreateDelegate(Type ^ type, System::Object ^ target, System::String ^ method, bool ignoreCase, bool throwOnBindFailure);
public static Delegate? CreateDelegate (Type type, object target, string method, bool ignoreCase, bool throwOnBindFailure);
public static Delegate CreateDelegate (Type type, object target, string method, bool ignoreCase, bool throwOnBindFailure);
static member CreateDelegate : Type * obj * string * bool * bool -> Delegate
Public Shared Function CreateDelegate (type As Type, target As Object, method As String, ignoreCase As Boolean, throwOnBindFailure As Boolean) As Delegate
Parameters
- target
- Object
The class instance on which method
is invoked.
- method
- String
The name of the instance method that the delegate is to represent.
- ignoreCase
- Boolean
A Boolean indicating whether to ignore the case when comparing the name of the method.
- throwOnBindFailure
- Boolean
true
to throw an exception if method
cannot be bound; otherwise, false
.
Returns
A delegate of the specified type that represents the specified instance method to invoke on the specified class instance.
Exceptions
type
does not inherit MulticastDelegate.
-or-
type
is not a RuntimeType
. See Runtime Types in Reflection.
-or-
method
is not an instance method.
-or-
method
cannot be bound, for example because it cannot be found, and throwOnBindFailure
is true
.
The Invoke
method of type
is not found.
The caller does not have the permissions necessary to access method
.
Remarks
This method creates delegates for instance methods only. An instance method is a method that is associated with an instance of a class; a static method is a method that is associated with the class itself.
Note
Starting with the .NET Framework 2.0 Service Pack 1, this method can be used to access non-public methods if the caller has been granted ReflectionPermission with the ReflectionPermissionFlag.RestrictedMemberAccess flag and if the grant set of the non-public methods is restricted to the caller's grant set, or a subset thereof. (See Security Considerations for Reflection.)
To use this functionality, your application should target the .NET Framework 3.5 or later.
See also
Applies to
CreateDelegate(Type, MethodInfo, Boolean)
Creates a delegate of the specified type to represent the specified static method, with the specified behavior on failure to bind.
public:
static Delegate ^ CreateDelegate(Type ^ type, System::Reflection::MethodInfo ^ method, bool throwOnBindFailure);
public static Delegate? CreateDelegate (Type type, System.Reflection.MethodInfo method, bool throwOnBindFailure);
public static Delegate CreateDelegate (Type type, System.Reflection.MethodInfo method, bool throwOnBindFailure);
static member CreateDelegate : Type * System.Reflection.MethodInfo * bool -> Delegate
Public Shared Function CreateDelegate (type As Type, method As MethodInfo, throwOnBindFailure As Boolean) As Delegate
Parameters
- method
- MethodInfo
The MethodInfo describing the static or instance method the delegate is to represent.
- throwOnBindFailure
- Boolean
true
to throw an exception if method
cannot be bound; otherwise, false
.
Returns
A delegate of the specified type to represent the specified static method.
Exceptions
type
does not inherit MulticastDelegate.
-or-
type
is not a RuntimeType
. See Runtime Types in Reflection.
-or-
method
cannot be bound, and throwOnBindFailure
is true
.
-or-
method
is not a RuntimeMethodInfo
. See Runtime Types in Reflection.
The Invoke
method of type
is not found.
The caller does not have the permissions necessary to access method
.
Examples
This section contains two code examples. The first example demonstrates the two kinds of delegates that can be created with this method overload: open over an instance method and open over a static method.
The second code example demonstrates compatible parameter types and return types.
Example 1
The following code example demonstrates the two ways a delegate can be created using this overload of the CreateDelegate method.
Note
There are two overloads of the CreateDelegate method that specify a MethodInfo but not a first argument; their functionality is the same except that one allows you to specify whether to throw on failure to bind, and the other always throws. This code example uses both overloads.
The example declares a class C
with a static method M2
and an instance method M1
, and two delegate types: D1
takes an instance of C
and a string, and D2
takes a string.
A second class named Example
contains the code that creates the delegates.
A delegate of type
D1
, representing an open instance method, is created for the instance methodM1
. An instance must be passed when the delegate is invoked.A delegate of type
D2
, representing an open static method, is created for the static methodM2
.
using System;
using System.Reflection;
using System.Security.Permissions;
// Declare three delegate types for demonstrating the combinations
// of static versus instance methods and open versus closed
// delegates.
//
public delegate void D1(C c, string s);
public delegate void D2(string s);
public delegate void D3();
// A sample class with an instance method and a static method.
//
public class C
{
private int id;
public C(int id) { this.id = id; }
public void M1(string s)
{
Console.WriteLine("Instance method M1 on C: id = {0}, s = {1}",
this.id, s);
}
public static void M2(string s)
{
Console.WriteLine("Static method M2 on C: s = {0}", s);
}
}
public class Example
{
public static void Main()
{
C c1 = new C(42);
// Get a MethodInfo for each method.
//
MethodInfo mi1 = typeof(C).GetMethod("M1",
BindingFlags.Public | BindingFlags.Instance);
MethodInfo mi2 = typeof(C).GetMethod("M2",
BindingFlags.Public | BindingFlags.Static);
D1 d1;
D2 d2;
D3 d3;
Console.WriteLine("\nAn instance method closed over C.");
// In this case, the delegate and the
// method must have the same list of argument types; use
// delegate type D2 with instance method M1.
//
Delegate test =
Delegate.CreateDelegate(typeof(D2), c1, mi1, false);
// Because false was specified for throwOnBindFailure
// in the call to CreateDelegate, the variable 'test'
// contains null if the method fails to bind (for
// example, if mi1 happened to represent a method of
// some class other than C).
//
if (test != null)
{
d2 = (D2) test;
// The same instance of C is used every time the
// delegate is invoked.
d2("Hello, World!");
d2("Hi, Mom!");
}
Console.WriteLine("\nAn open instance method.");
// In this case, the delegate has one more
// argument than the instance method; this argument comes
// at the beginning, and represents the hidden instance
// argument of the instance method. Use delegate type D1
// with instance method M1.
//
d1 = (D1) Delegate.CreateDelegate(typeof(D1), null, mi1);
// An instance of C must be passed in each time the
// delegate is invoked.
//
d1(c1, "Hello, World!");
d1(new C(5280), "Hi, Mom!");
Console.WriteLine("\nAn open static method.");
// In this case, the delegate and the method must
// have the same list of argument types; use delegate type
// D2 with static method M2.
//
d2 = (D2) Delegate.CreateDelegate(typeof(D2), null, mi2);
// No instances of C are involved, because this is a static
// method.
//
d2("Hello, World!");
d2("Hi, Mom!");
Console.WriteLine("\nA static method closed over the first argument (String).");
// The delegate must omit the first argument of the method.
// A string is passed as the firstArgument parameter, and
// the delegate is bound to this string. Use delegate type
// D3 with static method M2.
//
d3 = (D3) Delegate.CreateDelegate(typeof(D3),
"Hello, World!", mi2);
// Each time the delegate is invoked, the same string is
// used.
d3();
}
}
/* This code example produces the following output:
An instance method closed over C.
Instance method M1 on C: id = 42, s = Hello, World!
Instance method M1 on C: id = 42, s = Hi, Mom!
An open instance method.
Instance method M1 on C: id = 42, s = Hello, World!
Instance method M1 on C: id = 5280, s = Hi, Mom!
An open static method.
Static method M2 on C: s = Hello, World!
Static method M2 on C: s = Hi, Mom!
A static method closed over the first argument (String).
Static method M2 on C: s = Hello, World!
*/
open System
open System.Reflection
// A sample class with an instance method and a static method.
type C(id) =
member _.M1(s) =
printfn $"Instance method M1 on C: id = %i{id}, s = %s{s}"
static member M2(s) =
printfn $"Static method M2 on C: s = %s{s}"
// Declare three delegate types for demonstrating the combinations
// of static versus instance methods and open versus closed
// delegates.
type D1 = delegate of C * string -> unit
type D2 = delegate of string -> unit
type D3 = delegate of unit -> unit
let c1 = C 42
// Get a MethodInfo for each method.
//
let mi1 = typeof<C>.GetMethod("M1", BindingFlags.Public ||| BindingFlags.Instance)
let mi2 = typeof<C>.GetMethod("M2", BindingFlags.Public ||| BindingFlags.Static)
printfn "\nAn instance method closed over C."
// In this case, the delegate and the
// method must have the same list of argument types use
// delegate type D2 with instance method M1.
let test = Delegate.CreateDelegate(typeof<D2>, c1, mi1, false)
// Because false was specified for throwOnBindFailure
// in the call to CreateDelegate, the variable 'test'
// contains null if the method fails to bind (for
// example, if mi1 happened to represent a method of
// some class other than C).
if test <> null then
let d2 = test :?> D2
// The same instance of C is used every time the
// delegate is invoked.
d2.Invoke "Hello, World!"
d2.Invoke "Hi, Mom!"
printfn "\nAn open instance method."
// In this case, the delegate has one more
// argument than the instance method this argument comes
// at the beginning, and represents the hidden instance
// argument of the instance method. Use delegate type D1
// with instance method M1.
let d1 = Delegate.CreateDelegate(typeof<D1>, null, mi1) :?> D1
// An instance of C must be passed in each time the
// delegate is invoked.
d1.Invoke(c1, "Hello, World!")
d1.Invoke(C 5280, "Hi, Mom!")
printfn "\nAn open static method."
// In this case, the delegate and the method must
// have the same list of argument types use delegate type
// D2 with static method M2.
let d2 = Delegate.CreateDelegate(typeof<D2>, null, mi2) :?> D2
// No instances of C are involved, because this is a static
// method.
d2.Invoke "Hello, World!"
d2.Invoke "Hi, Mom!"
printfn "\nA static method closed over the first argument (String)."
// The delegate must omit the first argument of the method.
// A string is passed as the firstArgument parameter, and
// the delegate is bound to this string. Use delegate type
// D3 with static method M2.
let d3 = Delegate.CreateDelegate(typeof<D3>, "Hello, World!", mi2) :?> D3
// Each time the delegate is invoked, the same string is used.
d3.Invoke()
// This code example produces the following output:
// An instance method closed over C.
// Instance method M1 on C: id = 42, s = Hello, World!
// Instance method M1 on C: id = 42, s = Hi, Mom!
//
// An open instance method.
// Instance method M1 on C: id = 42, s = Hello, World!
// Instance method M1 on C: id = 5280, s = Hi, Mom!
//
// An open static method.
// Static method M2 on C: s = Hello, World!
// Static method M2 on C: s = Hi, Mom!
//
// A static method closed over the first argument (String).
// Static method M2 on C: s = Hello, World!
Imports System.Reflection
Imports System.Security.Permissions
' Declare three delegate types for demonstrating the combinations
' of Shared versus instance methods and open versus closed
' delegates.
'
Public Delegate Sub D1(ByVal c As C, ByVal s As String)
Public Delegate Sub D2(ByVal s As String)
Public Delegate Sub D3()
' A sample class with an instance method and a Shared method.
'
Public Class C
Private id As Integer
Public Sub New(ByVal id As Integer)
Me.id = id
End Sub
Public Sub M1(ByVal s As String)
Console.WriteLine("Instance method M1 on C: id = {0}, s = {1}", _
Me.id, s)
End Sub
Public Shared Sub M2(ByVal s As String)
Console.WriteLine("Shared method M2 on C: s = {0}", s)
End Sub
End Class
Public Class Example
Public Shared Sub Main()
Dim c1 As New C(42)
' Get a MethodInfo for each method.
'
Dim mi1 As MethodInfo = GetType(C).GetMethod("M1", _
BindingFlags.Public Or BindingFlags.Instance)
Dim mi2 As MethodInfo = GetType(C).GetMethod("M2", _
BindingFlags.Public Or BindingFlags.Static)
Dim d1 As D1
Dim d2 As D2
Dim d3 As D3
Console.WriteLine(vbLf & "An instance method closed over C.")
' In this case, the delegate and the
' method must have the same list of argument types; use
' delegate type D2 with instance method M1.
'
Dim test As [Delegate] = _
[Delegate].CreateDelegate(GetType(D2), c1, mi1, False)
' Because False was specified for throwOnBindFailure
' in the call to CreateDelegate, the variable 'test'
' contains Nothing if the method fails to bind (for
' example, if mi1 happened to represent a method of
' some class other than C).
'
If test IsNot Nothing Then
d2 = CType(test, D2)
' The same instance of C is used every time the
' delegate is invoked.
d2("Hello, World!")
d2("Hi, Mom!")
End If
Console.WriteLine(vbLf & "An open instance method.")
' In this case, the delegate has one more
' argument than the instance method; this argument comes
' at the beginning, and represents the hidden instance
' argument of the instance method. Use delegate type D1
' with instance method M1.
'
d1 = CType([Delegate].CreateDelegate(GetType(D1), Nothing, mi1), D1)
' An instance of C must be passed in each time the
' delegate is invoked.
'
d1(c1, "Hello, World!")
d1(New C(5280), "Hi, Mom!")
Console.WriteLine(vbLf & "An open Shared method.")
' In this case, the delegate and the method must
' have the same list of argument types; use delegate type
' D2 with Shared method M2.
'
d2 = CType([Delegate].CreateDelegate(GetType(D2), Nothing, mi2), D2)
' No instances of C are involved, because this is a Shared
' method.
'
d2("Hello, World!")
d2("Hi, Mom!")
Console.WriteLine(vbLf & "A Shared method closed over the first argument (String).")
' The delegate must omit the first argument of the method.
' A string is passed as the firstArgument parameter, and
' the delegate is bound to this string. Use delegate type
' D3 with Shared method M2.
'
d3 = CType([Delegate].CreateDelegate(GetType(D3), "Hello, World!", mi2), D3)
' Each time the delegate is invoked, the same string is
' used.
d3()
End Sub
End Class
' This code example produces the following output:
'
'An instance method closed over C.
'Instance method M1 on C: id = 42, s = Hello, World!
'Instance method M1 on C: id = 42, s = Hi, Mom!
'
'An open instance method.
'Instance method M1 on C: id = 42, s = Hello, World!
'Instance method M1 on C: id = 5280, s = Hi, Mom!
'
'An open Shared method.
'Shared method M2 on C: s = Hello, World!
'Shared method M2 on C: s = Hi, Mom!
'
'A Shared method closed over the first argument (String).
'Shared method M2 on C: s = Hello, World!
'
Example 2
The following code example demonstrates compatibility of parameter types and return types.
Note
This code example uses the CreateDelegate(Type, MethodInfo) method overload. The use of other overloads that take MethodInfo is similar.
The code example defines a base class named Base
and a class named Derived
that derives from Base
. The derived class has a static
(Shared
in Visual Basic) method named MyMethod
with one parameter of type Base
and a return type of Derived
. The code example also defines a delegate named Example
that has one parameter of type Derived
and a return type of Base
.
The code example demonstrates that the delegate named Example
can be used to represent the method MyMethod
. The method can be bound to the delegate because:
The parameter type of the delegate (
Derived
) is more restrictive than the parameter type ofMyMethod
(Base
), so that it is always safe to pass the argument of the delegate toMyMethod
.The return type of
MyMethod
(Derived
) is more restrictive than the parameter type of the delegate (Base
), so that it is always safe to cast the return type of the method to the return type of the delegate.
The code example produces no output.
using namespace System;
using namespace System::Reflection;
// Define two classes to use in the demonstration, a base class and
// a class that derives from it.
//
public ref class Base {};
public ref class Derived : Base
{
// Define a static method to use in the demonstration. The method
// takes an instance of Base and returns an instance of Derived.
// For the purposes of the demonstration, it is not necessary for
// the method to do anything useful.
//
public:
static Derived^ MyMethod(Base^ arg)
{
Base^ dummy = arg;
return gcnew Derived();
}
};
// Define a delegate that takes an instance of Derived and returns an
// instance of Base.
//
public delegate Base^ Example(Derived^ arg);
void main()
{
// The binding flags needed to retrieve MyMethod.
BindingFlags flags = BindingFlags::Public | BindingFlags::Static;
// Get a MethodInfo that represents MyMethod.
MethodInfo^ minfo = Derived::typeid->GetMethod("MyMethod", flags);
// Demonstrate contravariance of parameter types and covariance
// of return types by using the delegate Example to represent
// MyMethod. The delegate binds to the method because the
// parameter of the delegate is more restrictive than the
// parameter of the method (that is, the delegate accepts an
// instance of Derived, which can always be safely passed to
// a parameter of type Base), and the return type of MyMethod
// is more restrictive than the return type of Example (that
// is, the method returns an instance of Derived, which can
// always be safely cast to type Base).
//
Example^ ex =
(Example^) Delegate::CreateDelegate(Example::typeid, minfo);
// Execute MyMethod using the delegate Example.
//
Base^ b = ex(gcnew Derived());
}
using System;
using System.Reflection;
// Define two classes to use in the demonstration, a base class and
// a class that derives from it.
//
public class Base {}
public class Derived : Base
{
// Define a static method to use in the demonstration. The method
// takes an instance of Base and returns an instance of Derived.
// For the purposes of the demonstration, it is not necessary for
// the method to do anything useful.
//
public static Derived MyMethod(Base arg)
{
Base dummy = arg;
return new Derived();
}
}
// Define a delegate that takes an instance of Derived and returns an
// instance of Base.
//
public delegate Base Example(Derived arg);
class Test
{
public static void Main()
{
// The binding flags needed to retrieve MyMethod.
BindingFlags flags = BindingFlags.Public | BindingFlags.Static;
// Get a MethodInfo that represents MyMethod.
MethodInfo minfo = typeof(Derived).GetMethod("MyMethod", flags);
// Demonstrate contravariance of parameter types and covariance
// of return types by using the delegate Example to represent
// MyMethod. The delegate binds to the method because the
// parameter of the delegate is more restrictive than the
// parameter of the method (that is, the delegate accepts an
// instance of Derived, which can always be safely passed to
// a parameter of type Base), and the return type of MyMethod
// is more restrictive than the return type of Example (that
// is, the method returns an instance of Derived, which can
// always be safely cast to type Base).
//
Example ex =
(Example) Delegate.CreateDelegate(typeof(Example), minfo);
// Execute MyMethod using the delegate Example.
//
Base b = ex(new Derived());
}
}
open System
open System.Reflection
// Define two classes to use in the demonstration, a base class and
// a class that derives from it.
type Base() = class end
type Derived() =
inherit Base()
// Define a static method to use in the demonstration. The method
// takes an instance of Base and returns an instance of Derived.
// For the purposes of the demonstration, it is not necessary for
// the method to do anything useful.
static member MyMethod(arg: Base) =
Derived()
// Define a delegate that takes an instance of Derived and returns an
// instance of Base.
type Example = delegate of Derived -> Base
// The binding flags needed to retrieve MyMethod.
let flags = BindingFlags.Public ||| BindingFlags.Static
// Get a MethodInfo that represents MyMethod.
let minfo = typeof<Derived>.GetMethod("MyMethod", flags)
// Demonstrate contravariance of parameter types and covariance
// of return types by using the delegate Example to represent
// MyMethod. The delegate binds to the method because the
// parameter of the delegate is more restrictive than the
// parameter of the method (that is, the delegate accepts an
// instance of Derived, which can always be safely passed to
// a parameter of type Base), and the return type of MyMethod
// is more restrictive than the return type of Example (that
// is, the method returns an instance of Derived, which can
// always be safely cast to type Base).
let ex = Delegate.CreateDelegate(typeof<Example>, minfo) :?> Example
// Execute MyMethod using the delegate Example.
let b = Derived() |> ex.Invoke
Imports System.Reflection
' Define two classes to use in the demonstration, a base class and
' a class that derives from it.
'
Public Class Base
End Class
Public Class Derived
Inherits Base
' Define a Shared method to use in the demonstration. The method
' takes an instance of Base and returns an instance of Derived.
' For the purposes of the demonstration, it is not necessary for
' the method to do anything useful.
'
Public Shared Function MyMethod(ByVal arg As Base) As Derived
Dim dummy As Base = arg
Return New Derived()
End Function
End Class
' Define a delegate that takes an instance of Derived and returns an
' instance of Base.
'
Public Delegate Function Example(ByVal arg As Derived) As Base
Module Test
Sub Main()
' The binding flags needed to retrieve MyMethod.
Dim flags As BindingFlags = _
BindingFlags.Public Or BindingFlags.Static
' Get a MethodInfo that represents MyMethod.
Dim minfo As MethodInfo = _
GetType(Derived).GetMethod("MyMethod", flags)
' Demonstrate contravariance of parameter types and covariance
' of return types by using the delegate Example to represent
' MyMethod. The delegate binds to the method because the
' parameter of the delegate is more restrictive than the
' parameter of the method (that is, the delegate accepts an
' instance of Derived, which can always be safely passed to
' a parameter of type Base), and the return type of MyMethod
' is more restrictive than the return type of Example (that
' is, the method returns an instance of Derived, which can
' always be safely cast to type Base).
'
Dim ex As Example = CType( _
[Delegate].CreateDelegate(GetType(Example), minfo), _
Example _
)
' Execute MyMethod using the delegate Example.
'
Dim b As Base = ex(New Derived())
End Sub
End Module
Remarks
This method overload can create open static method delegates and open instance method delegates - that is, delegates that expose the hidden first argument of instance methods. For a detailed explanation, see the more general CreateDelegate(Type, Object, MethodInfo, Boolean) method overload, which allows you to create all combinations of open or closed delegates for instance or static methods.
Note
This method overload should be used when the delegate is not closed over its first argument, because it is somewhat faster in that case.
Note
Starting with the .NET Framework 2.0 Service Pack 1, this method can be used to access non-public methods if the caller has been granted ReflectionPermission with the ReflectionPermissionFlag.RestrictedMemberAccess flag and if the grant set of the non-public methods is restricted to the caller's grant set, or a subset thereof. (See Security Considerations for Reflection.)
To use this functionality, your application should target the .NET Framework 3.5 or later.
Compatible Parameter Types and Return Type
The parameter types and return type of a delegate must be compatible with the parameter types and return type of the method the delegate represents; the types do not have to match exactly.
A parameter of a delegate is compatible with the corresponding parameter of a method if the type of the delegate parameter is more restrictive than the type of the method parameter, because this guarantees that an argument passed to the delegate can be passed safely to the method.
Similarly, the return type of a delegate is compatible with the return type of a method if the return type of the method is more restrictive than the return type of the delegate, because this guarantees that the return value of the method can be cast safely to the return type of the delegate.
For example, a delegate with a parameter of type Hashtable and a return type of Object can represent a method with a parameter of type Object and a return value of type Hashtable.
See also
Applies to
CreateDelegate(Type, Object, String)
Creates a delegate of the specified type that represents the specified instance method to invoke on the specified class instance.
public:
static Delegate ^ CreateDelegate(Type ^ type, System::Object ^ target, System::String ^ method);
public static Delegate CreateDelegate (Type type, object target, string method);
static member CreateDelegate : Type * obj * string -> Delegate
Public Shared Function CreateDelegate (type As Type, target As Object, method As String) As Delegate
Parameters
- target
- Object
The class instance on which method
is invoked.
- method
- String
The name of the instance method that the delegate is to represent.
Returns
A delegate of the specified type that represents the specified instance method to invoke on the specified class instance.
Exceptions
type
does not inherit MulticastDelegate.
-or-
type
is not a RuntimeType
. See Runtime Types in Reflection.
-or-
method
is not an instance method.
-or-
method
cannot be bound, for example because it cannot be found.
The Invoke
method of type
is not found.
The caller does not have the permissions necessary to access method
.
Remarks
This method creates delegates for instance methods only. An instance method is a method that is associated with an instance of a class; a static method is a method that is associated with the class itself.
This method overload is equivalent to calling the CreateDelegate(Type, Object, String, Boolean, Boolean) method overload, specifying false
for ignoreCase
and true
for throwOnBindFailure
.
Note
Starting with the .NET Framework 2.0 Service Pack 1, this method can be used to access non-public methods if the caller has been granted ReflectionPermission with the ReflectionPermissionFlag.RestrictedMemberAccess flag and if the grant set of the non-public methods is restricted to the caller's grant set, or a subset thereof. (See Security Considerations for Reflection.)
To use this functionality, your application should target the .NET Framework 3.5 or later.
See also
Applies to
CreateDelegate(Type, Object, MethodInfo)
Creates a delegate of the specified type that represents the specified static or instance method, with the specified first argument.
public:
static Delegate ^ CreateDelegate(Type ^ type, System::Object ^ firstArgument, System::Reflection::MethodInfo ^ method);
public static Delegate CreateDelegate (Type type, object? firstArgument, System.Reflection.MethodInfo method);
public static Delegate CreateDelegate (Type type, object firstArgument, System.Reflection.MethodInfo method);
static member CreateDelegate : Type * obj * System.Reflection.MethodInfo -> Delegate
Public Shared Function CreateDelegate (type As Type, firstArgument As Object, method As MethodInfo) As Delegate
Parameters
- firstArgument
- Object
The object to which the delegate is bound, or null
to treat method
as static
(Shared
in Visual Basic).
- method
- MethodInfo
The MethodInfo describing the static or instance method the delegate is to represent.
Returns
A delegate of the specified type that represents the specified static or instance method.
Exceptions
type
does not inherit MulticastDelegate.
-or-
type
is not a RuntimeType
. See Runtime Types in Reflection.
-or-
method
cannot be bound.
-or-
method
is not a RuntimeMethodInfo
. See Runtime Types in Reflection.
The Invoke
method of type
is not found.
The caller does not have the permissions necessary to access method
.
Examples
This section contains three code examples. The first example demonstrates the four kinds of delegates that can be created: closed over an instance method, open over an instance method, open over a static method, and closed over a static method.
The second code example demonstrates compatible parameter types and return types.
The third code example defines a single delegate type, and shows all the methods that delegate type can represent.
Example 1
The following code example demonstrates the four ways a delegate can be created using this overload of the CreateDelegate method.
Note
There are two overloads of the CreateDelegate method that specify firstArgument
and a MethodInfo; their functionality is the same except that one allows you to specify whether to throw on failure to bind, and the other always throws. This code example uses both overloads.
The example declares a class C
with a static method M2
and an instance method M1
, and three delegate types: D1
takes an instance of C
and a string, D2
takes a string, and D3
has no arguments.
A second class named Example
contains the code that creates the delegates.
A delegate of type
D2
, closed over an instance ofC
, is created for the instance methodM1
. It is invoked with different strings, to show that the bound instance ofC
is always used.A delegate of type
D1
, representing an open instance method, is created for the instance methodM1
. An instance must be passed when the delegate is invoked.A delegate of type
D2
, representing an open static method, is created for the static methodM2
.Finally, a delegate of type
D3
, closed over a string, is created for the static methodM2
. The method is invoked to show that it uses the bound string.
using System;
using System.Reflection;
using System.Security.Permissions;
// Declare three delegate types for demonstrating the combinations
// of static versus instance methods and open versus closed
// delegates.
//
public delegate void D1(C c, string s);
public delegate void D2(string s);
public delegate void D3();
// A sample class with an instance method and a static method.
//
public class C
{
private int id;
public C(int id) { this.id = id; }
public void M1(string s)
{
Console.WriteLine("Instance method M1 on C: id = {0}, s = {1}",
this.id, s);
}
public static void M2(string s)
{
Console.WriteLine("Static method M2 on C: s = {0}", s);
}
}
public class Example
{
public static void Main()
{
C c1 = new C(42);
// Get a MethodInfo for each method.
//
MethodInfo mi1 = typeof(C).GetMethod("M1",
BindingFlags.Public | BindingFlags.Instance);
MethodInfo mi2 = typeof(C).GetMethod("M2",
BindingFlags.Public | BindingFlags.Static);
D1 d1;
D2 d2;
D3 d3;
Console.WriteLine("\nAn instance method closed over C.");
// In this case, the delegate and the
// method must have the same list of argument types; use
// delegate type D2 with instance method M1.
//
Delegate test =
Delegate.CreateDelegate(typeof(D2), c1, mi1, false);
// Because false was specified for throwOnBindFailure
// in the call to CreateDelegate, the variable 'test'
// contains null if the method fails to bind (for
// example, if mi1 happened to represent a method of
// some class other than C).
//
if (test != null)
{
d2 = (D2) test;
// The same instance of C is used every time the
// delegate is invoked.
d2("Hello, World!");
d2("Hi, Mom!");
}
Console.WriteLine("\nAn open instance method.");
// In this case, the delegate has one more
// argument than the instance method; this argument comes
// at the beginning, and represents the hidden instance
// argument of the instance method. Use delegate type D1
// with instance method M1.
//
d1 = (D1) Delegate.CreateDelegate(typeof(D1), null, mi1);
// An instance of C must be passed in each time the
// delegate is invoked.
//
d1(c1, "Hello, World!");
d1(new C(5280), "Hi, Mom!");
Console.WriteLine("\nAn open static method.");
// In this case, the delegate and the method must
// have the same list of argument types; use delegate type
// D2 with static method M2.
//
d2 = (D2) Delegate.CreateDelegate(typeof(D2), null, mi2);
// No instances of C are involved, because this is a static
// method.
//
d2("Hello, World!");
d2("Hi, Mom!");
Console.WriteLine("\nA static method closed over the first argument (String).");
// The delegate must omit the first argument of the method.
// A string is passed as the firstArgument parameter, and
// the delegate is bound to this string. Use delegate type
// D3 with static method M2.
//
d3 = (D3) Delegate.CreateDelegate(typeof(D3),
"Hello, World!", mi2);
// Each time the delegate is invoked, the same string is
// used.
d3();
}
}
/* This code example produces the following output:
An instance method closed over C.
Instance method M1 on C: id = 42, s = Hello, World!
Instance method M1 on C: id = 42, s = Hi, Mom!
An open instance method.
Instance method M1 on C: id = 42, s = Hello, World!
Instance method M1 on C: id = 5280, s = Hi, Mom!
An open static method.
Static method M2 on C: s = Hello, World!
Static method M2 on C: s = Hi, Mom!
A static method closed over the first argument (String).
Static method M2 on C: s = Hello, World!
*/
open System
open System.Reflection
// A sample class with an instance method and a static method.
type C(id) =
member _.M1(s) =
printfn $"Instance method M1 on C: id = %i{id}, s = %s{s}"
static member M2(s) =
printfn $"Static method M2 on C: s = %s{s}"
// Declare three delegate types for demonstrating the combinations
// of static versus instance methods and open versus closed
// delegates.
type D1 = delegate of C * string -> unit
type D2 = delegate of string -> unit
type D3 = delegate of unit -> unit
let c1 = C 42
// Get a MethodInfo for each method.
//
let mi1 = typeof<C>.GetMethod("M1", BindingFlags.Public ||| BindingFlags.Instance)
let mi2 = typeof<C>.GetMethod("M2", BindingFlags.Public ||| BindingFlags.Static)
printfn "\nAn instance method closed over C."
// In this case, the delegate and the
// method must have the same list of argument types use
// delegate type D2 with instance method M1.
let test = Delegate.CreateDelegate(typeof<D2>, c1, mi1, false)
// Because false was specified for throwOnBindFailure
// in the call to CreateDelegate, the variable 'test'
// contains null if the method fails to bind (for
// example, if mi1 happened to represent a method of
// some class other than C).
if test <> null then
let d2 = test :?> D2
// The same instance of C is used every time the
// delegate is invoked.
d2.Invoke "Hello, World!"
d2.Invoke "Hi, Mom!"
printfn "\nAn open instance method."
// In this case, the delegate has one more
// argument than the instance method this argument comes
// at the beginning, and represents the hidden instance
// argument of the instance method. Use delegate type D1
// with instance method M1.
let d1 = Delegate.CreateDelegate(typeof<D1>, null, mi1) :?> D1
// An instance of C must be passed in each time the
// delegate is invoked.
d1.Invoke(c1, "Hello, World!")
d1.Invoke(C 5280, "Hi, Mom!")
printfn "\nAn open static method."
// In this case, the delegate and the method must
// have the same list of argument types use delegate type
// D2 with static method M2.
let d2 = Delegate.CreateDelegate(typeof<D2>, null, mi2) :?> D2
// No instances of C are involved, because this is a static
// method.
d2.Invoke "Hello, World!"
d2.Invoke "Hi, Mom!"
printfn "\nA static method closed over the first argument (String)."
// The delegate must omit the first argument of the method.
// A string is passed as the firstArgument parameter, and
// the delegate is bound to this string. Use delegate type
// D3 with static method M2.
let d3 = Delegate.CreateDelegate(typeof<D3>, "Hello, World!", mi2) :?> D3
// Each time the delegate is invoked, the same string is used.
d3.Invoke()
// This code example produces the following output:
// An instance method closed over C.
// Instance method M1 on C: id = 42, s = Hello, World!
// Instance method M1 on C: id = 42, s = Hi, Mom!
//
// An open instance method.
// Instance method M1 on C: id = 42, s = Hello, World!
// Instance method M1 on C: id = 5280, s = Hi, Mom!
//
// An open static method.
// Static method M2 on C: s = Hello, World!
// Static method M2 on C: s = Hi, Mom!
//
// A static method closed over the first argument (String).
// Static method M2 on C: s = Hello, World!
Imports System.Reflection
Imports System.Security.Permissions
' Declare three delegate types for demonstrating the combinations
' of Shared versus instance methods and open versus closed
' delegates.
'
Public Delegate Sub D1(ByVal c As C, ByVal s As String)
Public Delegate Sub D2(ByVal s As String)
Public Delegate Sub D3()
' A sample class with an instance method and a Shared method.
'
Public Class C
Private id As Integer
Public Sub New(ByVal id As Integer)
Me.id = id
End Sub
Public Sub M1(ByVal s As String)
Console.WriteLine("Instance method M1 on C: id = {0}, s = {1}", _
Me.id, s)
End Sub
Public Shared Sub M2(ByVal s As String)
Console.WriteLine("Shared method M2 on C: s = {0}", s)
End Sub
End Class
Public Class Example
Public Shared Sub Main()
Dim c1 As New C(42)
' Get a MethodInfo for each method.
'
Dim mi1 As MethodInfo = GetType(C).GetMethod("M1", _
BindingFlags.Public Or BindingFlags.Instance)
Dim mi2 As MethodInfo = GetType(C).GetMethod("M2", _
BindingFlags.Public Or BindingFlags.Static)
Dim d1 As D1
Dim d2 As D2
Dim d3 As D3
Console.WriteLine(vbLf & "An instance method closed over C.")
' In this case, the delegate and the
' method must have the same list of argument types; use
' delegate type D2 with instance method M1.
'
Dim test As [Delegate] = _
[Delegate].CreateDelegate(GetType(D2), c1, mi1, False)
' Because False was specified for throwOnBindFailure
' in the call to CreateDelegate, the variable 'test'
' contains Nothing if the method fails to bind (for
' example, if mi1 happened to represent a method of
' some class other than C).
'
If test IsNot Nothing Then
d2 = CType(test, D2)
' The same instance of C is used every time the
' delegate is invoked.
d2("Hello, World!")
d2("Hi, Mom!")
End If
Console.WriteLine(vbLf & "An open instance method.")
' In this case, the delegate has one more
' argument than the instance method; this argument comes
' at the beginning, and represents the hidden instance
' argument of the instance method. Use delegate type D1
' with instance method M1.
'
d1 = CType([Delegate].CreateDelegate(GetType(D1), Nothing, mi1), D1)
' An instance of C must be passed in each time the
' delegate is invoked.
'
d1(c1, "Hello, World!")
d1(New C(5280), "Hi, Mom!")
Console.WriteLine(vbLf & "An open Shared method.")
' In this case, the delegate and the method must
' have the same list of argument types; use delegate type
' D2 with Shared method M2.
'
d2 = CType([Delegate].CreateDelegate(GetType(D2), Nothing, mi2), D2)
' No instances of C are involved, because this is a Shared
' method.
'
d2("Hello, World!")
d2("Hi, Mom!")
Console.WriteLine(vbLf & "A Shared method closed over the first argument (String).")
' The delegate must omit the first argument of the method.
' A string is passed as the firstArgument parameter, and
' the delegate is bound to this string. Use delegate type
' D3 with Shared method M2.
'
d3 = CType([Delegate].CreateDelegate(GetType(D3), "Hello, World!", mi2), D3)
' Each time the delegate is invoked, the same string is
' used.
d3()
End Sub
End Class
' This code example produces the following output:
'
'An instance method closed over C.
'Instance method M1 on C: id = 42, s = Hello, World!
'Instance method M1 on C: id = 42, s = Hi, Mom!
'
'An open instance method.
'Instance method M1 on C: id = 42, s = Hello, World!
'Instance method M1 on C: id = 5280, s = Hi, Mom!
'
'An open Shared method.
'Shared method M2 on C: s = Hello, World!
'Shared method M2 on C: s = Hi, Mom!
'
'A Shared method closed over the first argument (String).
'Shared method M2 on C: s = Hello, World!
'
Example 2
The following code example demonstrates compatibility of parameter types and return types.
Note
This code example uses the CreateDelegate(Type, MethodInfo) method overload. The use of other overloads that take MethodInfo is similar.
The code example defines a base class named Base
and a class named Derived
that derives from Base
. The derived class has a static
(Shared
in Visual Basic) method named MyMethod
with one parameter of type Base
and a return type of Derived
. The code example also defines a delegate named Example
that has one parameter of type Derived
and a return type of Base
.
The code example demonstrates that the delegate named Example
can be used to represent the method MyMethod
. The method can be bound to the delegate because:
The parameter type of the delegate (
Derived
) is more restrictive than the parameter type ofMyMethod
(Base
), so that it is always safe to pass the argument of the delegate toMyMethod
.The return type of
MyMethod
(Derived
) is more restrictive than the parameter type of the delegate (Base
), so that it is always safe to cast the return type of the method to the return type of the delegate.
The code example produces no output.
using namespace System;
using namespace System::Reflection;
// Define two classes to use in the demonstration, a base class and
// a class that derives from it.
//
public ref class Base {};
public ref class Derived : Base
{
// Define a static method to use in the demonstration. The method
// takes an instance of Base and returns an instance of Derived.
// For the purposes of the demonstration, it is not necessary for
// the method to do anything useful.
//
public:
static Derived^ MyMethod(Base^ arg)
{
Base^ dummy = arg;
return gcnew Derived();
}
};
// Define a delegate that takes an instance of Derived and returns an
// instance of Base.
//
public delegate Base^ Example(Derived^ arg);
void main()
{
// The binding flags needed to retrieve MyMethod.
BindingFlags flags = BindingFlags::Public | BindingFlags::Static;
// Get a MethodInfo that represents MyMethod.
MethodInfo^ minfo = Derived::typeid->GetMethod("MyMethod", flags);
// Demonstrate contravariance of parameter types and covariance
// of return types by using the delegate Example to represent
// MyMethod. The delegate binds to the method because the
// parameter of the delegate is more restrictive than the
// parameter of the method (that is, the delegate accepts an
// instance of Derived, which can always be safely passed to
// a parameter of type Base), and the return type of MyMethod
// is more restrictive than the return type of Example (that
// is, the method returns an instance of Derived, which can
// always be safely cast to type Base).
//
Example^ ex =
(Example^) Delegate::CreateDelegate(Example::typeid, minfo);
// Execute MyMethod using the delegate Example.
//
Base^ b = ex(gcnew Derived());
}
using System;
using System.Reflection;
// Define two classes to use in the demonstration, a base class and
// a class that derives from it.
//
public class Base {}
public class Derived : Base
{
// Define a static method to use in the demonstration. The method
// takes an instance of Base and returns an instance of Derived.
// For the purposes of the demonstration, it is not necessary for
// the method to do anything useful.
//
public static Derived MyMethod(Base arg)
{
Base dummy = arg;
return new Derived();
}
}
// Define a delegate that takes an instance of Derived and returns an
// instance of Base.
//
public delegate Base Example(Derived arg);
class Test
{
public static void Main()
{
// The binding flags needed to retrieve MyMethod.
BindingFlags flags = BindingFlags.Public | BindingFlags.Static;
// Get a MethodInfo that represents MyMethod.
MethodInfo minfo = typeof(Derived).GetMethod("MyMethod", flags);
// Demonstrate contravariance of parameter types and covariance
// of return types by using the delegate Example to represent
// MyMethod. The delegate binds to the method because the
// parameter of the delegate is more restrictive than the
// parameter of the method (that is, the delegate accepts an
// instance of Derived, which can always be safely passed to
// a parameter of type Base), and the return type of MyMethod
// is more restrictive than the return type of Example (that
// is, the method returns an instance of Derived, which can
// always be safely cast to type Base).
//
Example ex =
(Example) Delegate.CreateDelegate(typeof(Example), minfo);
// Execute MyMethod using the delegate Example.
//
Base b = ex(new Derived());
}
}
open System
open System.Reflection
// Define two classes to use in the demonstration, a base class and
// a class that derives from it.
type Base() = class end
type Derived() =
inherit Base()
// Define a static method to use in the demonstration. The method
// takes an instance of Base and returns an instance of Derived.
// For the purposes of the demonstration, it is not necessary for
// the method to do anything useful.
static member MyMethod(arg: Base) =
Derived()
// Define a delegate that takes an instance of Derived and returns an
// instance of Base.
type Example = delegate of Derived -> Base
// The binding flags needed to retrieve MyMethod.
let flags = BindingFlags.Public ||| BindingFlags.Static
// Get a MethodInfo that represents MyMethod.
let minfo = typeof<Derived>.GetMethod("MyMethod", flags)
// Demonstrate contravariance of parameter types and covariance
// of return types by using the delegate Example to represent
// MyMethod. The delegate binds to the method because the
// parameter of the delegate is more restrictive than the
// parameter of the method (that is, the delegate accepts an
// instance of Derived, which can always be safely passed to
// a parameter of type Base), and the return type of MyMethod
// is more restrictive than the return type of Example (that
// is, the method returns an instance of Derived, which can
// always be safely cast to type Base).
let ex = Delegate.CreateDelegate(typeof<Example>, minfo) :?> Example
// Execute MyMethod using the delegate Example.
let b = Derived() |> ex.Invoke
Imports System.Reflection
' Define two classes to use in the demonstration, a base class and
' a class that derives from it.
'
Public Class Base
End Class
Public Class Derived
Inherits Base
' Define a Shared method to use in the demonstration. The method
' takes an instance of Base and returns an instance of Derived.
' For the purposes of the demonstration, it is not necessary for
' the method to do anything useful.
'
Public Shared Function MyMethod(ByVal arg As Base) As Derived
Dim dummy As Base = arg
Return New Derived()
End Function
End Class
' Define a delegate that takes an instance of Derived and returns an
' instance of Base.
'
Public Delegate Function Example(ByVal arg As Derived) As Base
Module Test
Sub Main()
' The binding flags needed to retrieve MyMethod.
Dim flags As BindingFlags = _
BindingFlags.Public Or BindingFlags.Static
' Get a MethodInfo that represents MyMethod.
Dim minfo As MethodInfo = _
GetType(Derived).GetMethod("MyMethod", flags)
' Demonstrate contravariance of parameter types and covariance
' of return types by using the delegate Example to represent
' MyMethod. The delegate binds to the method because the
' parameter of the delegate is more restrictive than the
' parameter of the method (that is, the delegate accepts an
' instance of Derived, which can always be safely passed to
' a parameter of type Base), and the return type of MyMethod
' is more restrictive than the return type of Example (that
' is, the method returns an instance of Derived, which can
' always be safely cast to type Base).
'
Dim ex As Example = CType( _
[Delegate].CreateDelegate(GetType(Example), minfo), _
Example _
)
' Execute MyMethod using the delegate Example.
'
Dim b As Base = ex(New Derived())
End Sub
End Module
Example 3
The following code example shows all the methods a single delegate type can represent, using the CreateDelegate method to create the delegates.
Note
There are two overloads of the CreateDelegate method that specify firstArgument
and a MethodInfo; their functionality is the same except that one allows you to specify whether to throw on failure to bind, and the other always throws. This code example uses both overloads.
The code example defines two classes, C
and F
, and a delegate type D
with one argument of type C
. The classes have matching static and instance methods M1
, M3
, and M4
, and class C
also has an instance method M2
that has no arguments.
A third class named Example
contains the code that creates the delegates.
Delegates are created for instance method
M1
of typeC
and typeF
; each is closed over an instance of the respective type. MethodM1
of typeC
displays theID
properties of the bound instance and of the argument.A delegate is created for method
M2
of typeC
. This is an open instance delegate, in which the argument of the delegate represents the hidden first argument on the instance method. The method has no other arguments. It is called as if it were a static method.Delegates are created for static method
M3
of typeC
and typeF
; these are open static delegates.Finally, delegates are created for static method
M4
of typeC
and typeF
; each method has the declaring type as its first argument, and an instance of the type is supplied, so the delegates are closed over their first arguments. MethodM4
of typeC
displays theID
properties of the bound instance and of the argument.
using System;
using System.Reflection;
using System.Security.Permissions;
// Declare a delegate type. The object of this code example
// is to show all the methods this delegate can bind to.
//
public delegate void D(C c);
// Declare two sample classes, C and F. Class C has an ID
// property so instances can be identified.
//
public class C
{
private int id;
public int ID { get { return id; }}
public C(int id) { this.id = id; }
public void M1(C c)
{
Console.WriteLine("Instance method M1(C c) on C: this.id = {0}, c.ID = {1}",
this.id, c.ID);
}
public void M2()
{
Console.WriteLine("Instance method M2() on C: this.id = {0}",
this.id);
}
public static void M3(C c)
{
Console.WriteLine("Static method M3(C c) on C: c.ID = {0}", c.ID);
}
public static void M4(C c1, C c2)
{
Console.WriteLine("Static method M4(C c1, C c2) on C: c1.ID = {0}, c2.ID = {1}",
c1.ID, c2.ID);
}
}
public class F
{
public void M1(C c)
{
Console.WriteLine("Instance method M1(C c) on F: c.ID = {0}",
c.ID);
}
public static void M3(C c)
{
Console.WriteLine("Static method M3(C c) on F: c.ID = {0}", c.ID);
}
public static void M4(F f, C c)
{
Console.WriteLine("Static method M4(F f, C c) on F: c.ID = {0}",
c.ID);
}
}
public class Example
{
public static void Main()
{
C c1 = new C(42);
C c2 = new C(1491);
F f1 = new F();
D d;
// Instance method with one argument of type C.
MethodInfo cmi1 = typeof(C).GetMethod("M1");
// Instance method with no arguments.
MethodInfo cmi2 = typeof(C).GetMethod("M2");
// Static method with one argument of type C.
MethodInfo cmi3 = typeof(C).GetMethod("M3");
// Static method with two arguments of type C.
MethodInfo cmi4 = typeof(C).GetMethod("M4");
// Instance method with one argument of type C.
MethodInfo fmi1 = typeof(F).GetMethod("M1");
// Static method with one argument of type C.
MethodInfo fmi3 = typeof(F).GetMethod("M3");
// Static method with an argument of type F and an argument
// of type C.
MethodInfo fmi4 = typeof(F).GetMethod("M4");
Console.WriteLine("\nAn instance method on any type, with an argument of type C.");
// D can represent any instance method that exactly matches its
// signature. Methods on C and F are shown here.
//
d = (D) Delegate.CreateDelegate(typeof(D), c1, cmi1);
d(c2);
d = (D) Delegate.CreateDelegate(typeof(D), f1, fmi1);
d(c2);
Console.WriteLine("\nAn instance method on C with no arguments.");
// D can represent an instance method on C that has no arguments;
// in this case, the argument of D represents the hidden first
// argument of any instance method. The delegate acts like a
// static method, and an instance of C must be passed each time
// it is invoked.
//
d = (D) Delegate.CreateDelegate(typeof(D), null, cmi2);
d(c1);
Console.WriteLine("\nA static method on any type, with an argument of type C.");
// D can represent any static method with the same signature.
// Methods on F and C are shown here.
//
d = (D) Delegate.CreateDelegate(typeof(D), null, cmi3);
d(c1);
d = (D) Delegate.CreateDelegate(typeof(D), null, fmi3);
d(c1);
Console.WriteLine("\nA static method on any type, with an argument of");
Console.WriteLine(" that type and an argument of type C.");
// D can represent any static method with one argument of the
// type the method belongs and a second argument of type C.
// In this case, the method is closed over the instance of
// supplied for the its first argument, and acts like an instance
// method. Methods on F and C are shown here.
//
d = (D) Delegate.CreateDelegate(typeof(D), c1, cmi4);
d(c2);
Delegate test =
Delegate.CreateDelegate(typeof(D), f1, fmi4, false);
// This final example specifies false for throwOnBindFailure
// in the call to CreateDelegate, so the variable 'test'
// contains Nothing if the method fails to bind (for
// example, if fmi4 happened to represent a method of
// some class other than F).
//
if (test != null)
{
d = (D) test;
d(c2);
}
}
}
/* This code example produces the following output:
An instance method on any type, with an argument of type C.
Instance method M1(C c) on C: this.id = 42, c.ID = 1491
Instance method M1(C c) on F: c.ID = 1491
An instance method on C with no arguments.
Instance method M2() on C: this.id = 42
A static method on any type, with an argument of type C.
Static method M3(C c) on C: c.ID = 42
Static method M3(C c) on F: c.ID = 42
A static method on any type, with an argument of
that type and an argument of type C.
Static method M4(C c1, C c2) on C: c1.ID = 42, c2.ID = 1491
Static method M4(F f, C c) on F: c.ID = 1491
*/
open System
// Declare two sample classes, C and F. Class C has an ID
// property so instances can be identified.
type C(id) =
member _.ID = id
member _.M1(c: C) =
printfn $"Instance method M1(C c) on C: this.id = {id}, c.ID = {c.ID}"
member _.M2() =
printfn $"Instance method M2() on C: this.id = {id}"
static member M3(c: C) =
printfn $"Static method M3(C c) on C: c.ID = {c.ID}"
static member M4(c1: C, c2: C) =
printfn $"Static method M4(C c1, C c2) on C: c1.ID = {c1.ID}, c2.ID = {c2.ID}"
// Declare a delegate type. The object of this code example
// is to show all the methods this delegate can bind to.
type D = delegate of C -> unit
type F() =
member _.M1(c: C) =
printfn $"Instance method M1(C c) on F: c.ID = {c.ID}"
member _.M3(c: C) =
printfn $"Static method M3(C c) on F: c.ID = {c.ID}"
member _.M4(f: F, c: C) =
printfn $"Static method M4(F f, C c) on F: c.ID = {c.ID}"
[<EntryPoint>]
let main _ =
let c1 = C 42
let c2 = C 1491
let f1 = F()
// Instance method with one argument of type C.
let cmi1 = typeof<C>.GetMethod "M1"
// Instance method with no arguments.
let cmi2 = typeof<C>.GetMethod "M2"
// Static method with one argument of type C.
let cmi3 = typeof<C>.GetMethod "M3"
// Static method with two arguments of type C.
let cmi4 = typeof<C>.GetMethod "M4"
// Instance method with one argument of type C.
let fmi1 = typeof<F>.GetMethod "M1"
// Static method with one argument of type C.
let fmi3 = typeof<F>.GetMethod "M3"
// Static method with an argument of type F and an argument
// of type C.
let fmi4 = typeof<F>.GetMethod "M4"
printfn "\nAn instance method on any type, with an argument of type C."
// D can represent any instance method that exactly matches its
// signature. Methods on C and F are shown here.
let d = Delegate.CreateDelegate(typeof<D>, c1, cmi1) :?> D
d.Invoke c2
let d = Delegate.CreateDelegate(typeof<D>, f1, fmi1) :?> D
d.Invoke c2
Console.WriteLine("\nAn instance method on C with no arguments.")
// D can represent an instance method on C that has no arguments
// in this case, the argument of D represents the hidden first
// argument of any instance method. The delegate acts like a
// static method, and an instance of C must be passed each time
// it is invoked.
let d = Delegate.CreateDelegate(typeof<D>, null, cmi2) :?> D
d.Invoke c1
printfn "\nA static method on any type, with an argument of type C."
// D can represent any static method with the same signature.
// Methods on F and C are shown here.
let d = Delegate.CreateDelegate(typeof<D>, null, cmi3) :?> D
d.Invoke c1
let d = Delegate.CreateDelegate(typeof<D>, null, fmi3) :?> D
d.Invoke c1
printfn "\nA static method on any type, with an argument of"
printfn " that type and an argument of type C."
// D can represent any static method with one argument of the
// type the method belongs and a second argument of type C.
// In this case, the method is closed over the instance of
// supplied for the its first argument, and acts like an instance
// method. Methods on F and C are shown here.
let d = Delegate.CreateDelegate(typeof<D>, c1, cmi4) :?> D
d.Invoke c2
let test =
Delegate.CreateDelegate(typeof<D>, f1, fmi4, false)
// This final example specifies false for throwOnBindFailure
// in the call to CreateDelegate, so the variable 'test'
// contains Nothing if the method fails to bind (for
// example, if fmi4 happened to represent a method of
// some class other than F).
match test with
| :? D as d ->
d.Invoke c2
| _ -> ()
0
// This code example produces the following output:
// An instance method on any type, with an argument of type C.
// Instance method M1(C c) on C: this.id = 42, c.ID = 1491
// Instance method M1(C c) on F: c.ID = 1491
//
// An instance method on C with no arguments.
// Instance method M2() on C: this.id = 42
//
// A static method on any type, with an argument of type C.
// Static method M3(C c) on C: c.ID = 42
// Static method M3(C c) on F: c.ID = 42
//
// A static method on any type, with an argument of
// that type and an argument of type C.
// Static method M4(C c1, C c2) on C: c1.ID = 42, c2.ID = 1491
// Static method M4(F f, C c) on F: c.ID = 1491
Imports System.Reflection
Imports System.Security.Permissions
' Declare a delegate type. The object of this code example
' is to show all the methods this delegate can bind to.
'
Public Delegate Sub D(ByVal c As C)
' Declare two sample classes, C and F. Class C has an ID
' property so instances can be identified.
'
Public Class C
Private _id As Integer
Public ReadOnly Property ID() As Integer
Get
Return _id
End Get
End Property
Public Sub New(ByVal newId As Integer)
Me._id = newId
End Sub
Public Sub M1(ByVal c As C)
Console.WriteLine("Instance method M1(c As C) on C: this.id = {0}, c.ID = {1}", _
Me.id, c.ID)
End Sub
Public Sub M2()
Console.WriteLine("Instance method M2() on C: this.id = {0}", Me.id)
End Sub
Public Shared Sub M3(ByVal c As C)
Console.WriteLine("Shared method M3(c As C) on C: c.ID = {0}", c.ID)
End Sub
Public Shared Sub M4(ByVal c1 As C, ByVal c2 As C)
Console.WriteLine("Shared method M4(c1 As C, c2 As C) on C: c1.ID = {0}, c2.ID = {1}", _
c1.ID, c2.ID)
End Sub
End Class
Public Class F
Public Sub M1(ByVal c As C)
Console.WriteLine("Instance method M1(c As C) on F: c.ID = {0}", c.ID)
End Sub
Public Shared Sub M3(ByVal c As C)
Console.WriteLine("Shared method M3(c As C) on F: c.ID = {0}", c.ID)
End Sub
Public Shared Sub M4(ByVal f As F, ByVal c As C)
Console.WriteLine("Shared method M4(f As F, c As C) on F: c.ID = {0}", c.ID)
End Sub
End Class
Public Class Example
Public Shared Sub Main()
Dim c1 As New C(42)
Dim c2 As New C(1491)
Dim f1 As New F()
Dim d As D
' Instance method with one argument of type C.
Dim cmi1 As MethodInfo = GetType(C).GetMethod("M1")
' Instance method with no arguments.
Dim cmi2 As MethodInfo = GetType(C).GetMethod("M2")
' Shared method with one argument of type C.
Dim cmi3 As MethodInfo = GetType(C).GetMethod("M3")
' Shared method with two arguments of type C.
Dim cmi4 As MethodInfo = GetType(C).GetMethod("M4")
' Instance method with one argument of type C.
Dim fmi1 As MethodInfo = GetType(F).GetMethod("M1")
' Shared method with one argument of type C.
Dim fmi3 As MethodInfo = GetType(F).GetMethod("M3")
' Shared method with an argument of type F and an
' argument of type C.
Dim fmi4 As MethodInfo = GetType(F).GetMethod("M4")
Console.WriteLine(vbLf & "An instance method on any type, with an argument of type C.")
' D can represent any instance method that exactly matches its
' signature. Methods on C and F are shown here.
'
d = CType([Delegate].CreateDelegate(GetType(D), c1, cmi1), D)
d(c2)
d = CType([Delegate].CreateDelegate(GetType(D), f1, fmi1), D)
d(c2)
Console.WriteLine(vbLf & "An instance method on C with no arguments.")
' D can represent an instance method on C that has no arguments;
' in this case, the argument of D represents the hidden first
' argument of any instance method. The delegate acts like a
' Shared method, and an instance of C must be passed each time
' it is invoked.
'
d = CType([Delegate].CreateDelegate(GetType(D), Nothing, cmi2), D)
d(c1)
Console.WriteLine(vbLf & "A Shared method on any type, with an argument of type C.")
' D can represent any Shared method with the same signature.
' Methods on F and C are shown here.
'
d = CType([Delegate].CreateDelegate(GetType(D), Nothing, cmi3), D)
d(c1)
d = CType([Delegate].CreateDelegate(GetType(D), Nothing, fmi3), D)
d(c1)
Console.WriteLine(vbLf & "A Shared method on any type, with an argument of")
Console.WriteLine(" that type and an argument of type C.")
' D can represent any Shared method with one argument of the
' type the method belongs and a second argument of type C.
' In this case, the method is closed over the instance of
' supplied for the its first argument, and acts like an instance
' method. Methods on F and C are shown here.
'
d = CType([Delegate].CreateDelegate(GetType(D), c1, cmi4), D)
d(c2)
Dim test As [Delegate] = _
[Delegate].CreateDelegate(GetType(D), f1, fmi4, false)
' This final example specifies False for throwOnBindFailure
' in the call to CreateDelegate, so the variable 'test'
' contains Nothing if the method fails to bind (for
' example, if fmi4 happened to represent a method of
' some class other than F).
'
If test IsNot Nothing Then
d = CType(test, D)
d(c2)
End If
End Sub
End Class
' This code example produces the following output:
'
'An instance method on any type, with an argument of type C.
'Instance method M1(c As C) on C: this.id = 42, c.ID = 1491
'Instance method M1(c As C) on F: c.ID = 1491
'
'An instance method on C with no arguments.
'Instance method M2() on C: this.id = 42
'
'A Shared method on any type, with an argument of type C.
'Shared method M3(c As C) on C: c.ID = 42
'Shared method M3(c As C) on F: c.ID = 42
'
'A Shared method on any type, with an argument of
' that type and an argument of type C.
'Shared method M4(c1 As C, c2 As C) on C: c1.ID = 42, c2.ID = 1491
'Shared method M4(f As F, c As C) on F: c.ID = 1491
'
Remarks
Calling this method overload is equivalent to calling the CreateDelegate(Type, Object, MethodInfo, Boolean) method overload and specifying true
for throwOnBindFailure
. These two overloads provide the most flexible way to create delegates. You can use them to create delegates for either static or instance methods, and optionally to specify the first argument.
Note
If you do not supply a first argument, use the CreateDelegate(Type, MethodInfo) method overload for better performance.
The delegate type and the method must have compatible return types. That is, the return type of method
must be assignable to the return type of type
.
If firstArgument
is supplied, it is passed to method
every time the delegate is invoked; firstArgument
is said to be bound to the delegate, and the delegate is said to be closed over its first argument. If method
is static
(Shared
in Visual Basic), the argument list supplied when invoking the delegate includes all parameters except the first; if method
is an instance method, then firstArgument
is passed to the hidden instance parameter (represented by this
in C#, or by Me
in Visual Basic).
If firstArgument
is supplied, the first parameter of method
must be a reference type, and firstArgument
must be compatible with that type.
Important
If method
is static
(Shared
in Visual Basic) and its first parameter is of type Object or ValueType, then firstArgument
can be a value type. In this case firstArgument
is automatically boxed. Automatic boxing does not occur for any other arguments, as it would in a C# or Visual Basic function call.
If firstArgument
is a null reference and method
is an instance method, the result depends on the signatures of the delegate type type
and of method
:
If the signature of
type
explicitly includes the hidden first parameter ofmethod
, the delegate is said to represent an open instance method. When the delegate is invoked, the first argument in the argument list is passed to the hidden instance parameter ofmethod
.If the signatures of
method
andtype
match (that is, all parameter types are compatible), then the delegate is said to be closed over a null reference. Invoking the delegate is like calling an instance method on a null instance, which is not a particularly useful thing to do.
If firstArgument
is a null reference and method
is static, the result depends on the signatures of the delegate type type
and of method
:
If the signature of
method
andtype
match (that is, all parameter types are compatible), the delegate is said to represent an open static method. This is the most common case for static methods. In this case, you can get slightly better performance by using the CreateDelegate(Type, MethodInfo) method overload.If the signature of
type
begins with the second parameter ofmethod
and the rest of the parameter types are compatible, then the delegate is said to be closed over a null reference. When the delegate is invoked, a null reference is passed to the first parameter ofmethod
.
Note
Starting with the .NET Framework 2.0 Service Pack 1, this method can be used to access non-public methods if the caller has been granted ReflectionPermission with the ReflectionPermissionFlag.RestrictedMemberAccess flag and if the grant set of the non-public methods is restricted to the caller's grant set, or a subset thereof. (See Security Considerations for Reflection.)
To use this functionality, your application should target the .NET Framework 3.5 or later.
Compatible Parameter Types and Return Type
The parameter types and return type of a delegate must be compatible with the parameter types and return type of the method the delegate represents; the types do not have to match exactly.
A parameter of a delegate is compatible with the corresponding parameter of a method if the type of the delegate parameter is more restrictive than the type of the method parameter, because this guarantees that an argument passed to the delegate can be passed safely to the method.
Similarly, the return type of a delegate is compatible with the return type of a method if the return type of the method is more restrictive than the return type of the delegate, because this guarantees that the return value of the method can be cast safely to the return type of the delegate.
For example, a delegate with a parameter of type Hashtable and a return type of Object can represent a method with a parameter of type Object and a return value of type Hashtable.
Determining the Methods a Delegate Can Represent
Another useful way to think of the flexibility provided by this overload of CreateDelegate is that any given delegate can represent four different combinations of method signature and method kind (static versus instance). Consider a delegate type D
with one argument of type C
. The following describes the methods D
can represent, ignoring the return type since it must match in all cases:
D
can represent any instance method that has exactly one argument of typeC
, regardless of what type the instance method belongs to. When CreateDelegate is called,firstArgument
is an instance of the typemethod
belongs to, and the resulting delegate is said to be closed over that instance. (Trivially,D
can also be closed over a null reference iffirstArgument
is a null reference.)D
can represent an instance method ofC
that has no arguments. When CreateDelegate is called,firstArgument
is a null reference. The resulting delegate represents an open instance method, and an instance ofC
must be supplied each time it is invoked.D
can represent a static method that takes one argument of typeC
, and that method can belong to any type. When CreateDelegate is called,firstArgument
is a null reference. The resulting delegate represents an open static method, and an instance ofC
must be supplied each time it is invoked.D
can represent a static method that belongs to typeF
and has two arguments, of typeF
and typeC
. When CreateDelegate is called,firstArgument
is an instance ofF
. The resulting delegate represents a static method that is closed over that instance ofF
. Note that in the case whereF
andC
are the same type, the static method has two arguments of that type. (In this case,D
is closed over a null reference iffirstArgument
is a null reference.)
See also
Applies to
CreateDelegate(Type, Type, String)
Creates a delegate of the specified type that represents the specified static method of the specified class.
public:
static Delegate ^ CreateDelegate(Type ^ type, Type ^ target, System::String ^ method);
public static Delegate CreateDelegate (Type type, Type target, string method);
static member CreateDelegate : Type * Type * string -> Delegate
Public Shared Function CreateDelegate (type As Type, target As Type, method As String) As Delegate
Parameters
- method
- String
The name of the static method that the delegate is to represent.
Returns
A delegate of the specified type that represents the specified static method of the specified class.
Exceptions
type
does not inherit MulticastDelegate.
-or-
type
is not a RuntimeType
. See Runtime Types in Reflection.
-or-
target
is not a RuntimeType
.
-or-
target
is an open generic type. That is, its ContainsGenericParameters property is true
.
-or-
method
is not a static
method (Shared
method in Visual Basic).
-or-
method
cannot be bound, for example because it cannot be found, and throwOnBindFailure
is true
.
The Invoke
method of type
is not found.
The caller does not have the permissions necessary to access method
.
Remarks
This method creates delegates for static methods only. An instance method is a method that is associated with an instance of a class; a static method is a method that is associated with the class itself.
This method overload is equivalent to calling the CreateDelegate(Type, Type, String, Boolean, Boolean) method overload, specifying false
for ignoreCase
and true
for throwOnBindFailure
.
Note
Starting with the .NET Framework 2.0 Service Pack 1, this method can be used to access non-public methods if the caller has been granted ReflectionPermission with the ReflectionPermissionFlag.RestrictedMemberAccess flag and if the grant set of the non-public methods is restricted to the caller's grant set, or a subset thereof. (See Security Considerations for Reflection.)
To use this functionality, your application should target the .NET Framework 3.5 or later.
See also
Applies to
CreateDelegate(Type, MethodInfo)
Creates a delegate of the specified type to represent the specified method.
public:
static Delegate ^ CreateDelegate(Type ^ type, System::Reflection::MethodInfo ^ method);
public static Delegate CreateDelegate (Type type, System.Reflection.MethodInfo method);
static member CreateDelegate : Type * System.Reflection.MethodInfo -> Delegate
Public Shared Function CreateDelegate (type As Type, method As MethodInfo) As Delegate
Parameters
- method
- MethodInfo
The MethodInfo describing the static or instance method the delegate is to represent.
Returns
A delegate of the specified type to represent the specified method.
Exceptions
type
does not inherit MulticastDelegate.
-or-
type
is not a RuntimeType
. See Runtime Types in Reflection.
-or-
method
cannot be bound.
-or-
method
is not a RuntimeMethodInfo
. See Runtime Types in Reflection.
The Invoke
method of type
is not found.
The caller does not have the permissions necessary to access method
.
Examples
This section contains two code examples. The first example demonstrates the two kinds of delegates that can be created with this method overload: open over an instance method and open over a static method.
The second code example demonstrates compatible parameter types and return types.
Example 1
The following code example demonstrates the two ways a delegate can be created using this overload of the CreateDelegate method.
Note
There are two overloads of the CreateDelegate method that specify a MethodInfo but not a first argument; their functionality is the same except that one allows you to specify whether to throw on failure to bind, and the other always throws. This code example uses both overloads.
The example declares a class C
with a static method M2
and an instance method M1
, and two delegate types: D1
takes an instance of C
and a string, and D2
takes a string.
A second class named Example
contains the code that creates the delegates.
A delegate of type
D1
, representing an open instance method, is created for the instance methodM1
. An instance must be passed when the delegate is invoked.A delegate of type
D2
, representing an open static method, is created for the static methodM2
.
using System;
using System.Reflection;
using System.Security.Permissions;
// Declare three delegate types for demonstrating the combinations
// of static versus instance methods and open versus closed
// delegates.
//
public delegate void D1(C c, string s);
public delegate void D2(string s);
public delegate void D3();
// A sample class with an instance method and a static method.
//
public class C
{
private int id;
public C(int id) { this.id = id; }
public void M1(string s)
{
Console.WriteLine("Instance method M1 on C: id = {0}, s = {1}",
this.id, s);
}
public static void M2(string s)
{
Console.WriteLine("Static method M2 on C: s = {0}", s);
}
}
public class Example
{
public static void Main()
{
C c1 = new C(42);
// Get a MethodInfo for each method.
//
MethodInfo mi1 = typeof(C).GetMethod("M1",
BindingFlags.Public | BindingFlags.Instance);
MethodInfo mi2 = typeof(C).GetMethod("M2",
BindingFlags.Public | BindingFlags.Static);
D1 d1;
D2 d2;
D3 d3;
Console.WriteLine("\nAn instance method closed over C.");
// In this case, the delegate and the
// method must have the same list of argument types; use
// delegate type D2 with instance method M1.
//
Delegate test =
Delegate.CreateDelegate(typeof(D2), c1, mi1, false);
// Because false was specified for throwOnBindFailure
// in the call to CreateDelegate, the variable 'test'
// contains null if the method fails to bind (for
// example, if mi1 happened to represent a method of
// some class other than C).
//
if (test != null)
{
d2 = (D2) test;
// The same instance of C is used every time the
// delegate is invoked.
d2("Hello, World!");
d2("Hi, Mom!");
}
Console.WriteLine("\nAn open instance method.");
// In this case, the delegate has one more
// argument than the instance method; this argument comes
// at the beginning, and represents the hidden instance
// argument of the instance method. Use delegate type D1
// with instance method M1.
//
d1 = (D1) Delegate.CreateDelegate(typeof(D1), null, mi1);
// An instance of C must be passed in each time the
// delegate is invoked.
//
d1(c1, "Hello, World!");
d1(new C(5280), "Hi, Mom!");
Console.WriteLine("\nAn open static method.");
// In this case, the delegate and the method must
// have the same list of argument types; use delegate type
// D2 with static method M2.
//
d2 = (D2) Delegate.CreateDelegate(typeof(D2), null, mi2);
// No instances of C are involved, because this is a static
// method.
//
d2("Hello, World!");
d2("Hi, Mom!");
Console.WriteLine("\nA static method closed over the first argument (String).");
// The delegate must omit the first argument of the method.
// A string is passed as the firstArgument parameter, and
// the delegate is bound to this string. Use delegate type
// D3 with static method M2.
//
d3 = (D3) Delegate.CreateDelegate(typeof(D3),
"Hello, World!", mi2);
// Each time the delegate is invoked, the same string is
// used.
d3();
}
}
/* This code example produces the following output:
An instance method closed over C.
Instance method M1 on C: id = 42, s = Hello, World!
Instance method M1 on C: id = 42, s = Hi, Mom!
An open instance method.
Instance method M1 on C: id = 42, s = Hello, World!
Instance method M1 on C: id = 5280, s = Hi, Mom!
An open static method.
Static method M2 on C: s = Hello, World!
Static method M2 on C: s = Hi, Mom!
A static method closed over the first argument (String).
Static method M2 on C: s = Hello, World!
*/
open System
open System.Reflection
// A sample class with an instance method and a static method.
type C(id) =
member _.M1(s) =
printfn $"Instance method M1 on C: id = %i{id}, s = %s{s}"
static member M2(s) =
printfn $"Static method M2 on C: s = %s{s}"
// Declare three delegate types for demonstrating the combinations
// of static versus instance methods and open versus closed
// delegates.
type D1 = delegate of C * string -> unit
type D2 = delegate of string -> unit
type D3 = delegate of unit -> unit
let c1 = C 42
// Get a MethodInfo for each method.
//
let mi1 = typeof<C>.GetMethod("M1", BindingFlags.Public ||| BindingFlags.Instance)
let mi2 = typeof<C>.GetMethod("M2", BindingFlags.Public ||| BindingFlags.Static)
printfn "\nAn instance method closed over C."
// In this case, the delegate and the
// method must have the same list of argument types use
// delegate type D2 with instance method M1.
let test = Delegate.CreateDelegate(typeof<D2>, c1, mi1, false)
// Because false was specified for throwOnBindFailure
// in the call to CreateDelegate, the variable 'test'
// contains null if the method fails to bind (for
// example, if mi1 happened to represent a method of
// some class other than C).
if test <> null then
let d2 = test :?> D2
// The same instance of C is used every time the
// delegate is invoked.
d2.Invoke "Hello, World!"
d2.Invoke "Hi, Mom!"
printfn "\nAn open instance method."
// In this case, the delegate has one more
// argument than the instance method this argument comes
// at the beginning, and represents the hidden instance
// argument of the instance method. Use delegate type D1
// with instance method M1.
let d1 = Delegate.CreateDelegate(typeof<D1>, null, mi1) :?> D1
// An instance of C must be passed in each time the
// delegate is invoked.
d1.Invoke(c1, "Hello, World!")
d1.Invoke(C 5280, "Hi, Mom!")
printfn "\nAn open static method."
// In this case, the delegate and the method must
// have the same list of argument types use delegate type
// D2 with static method M2.
let d2 = Delegate.CreateDelegate(typeof<D2>, null, mi2) :?> D2
// No instances of C are involved, because this is a static
// method.
d2.Invoke "Hello, World!"
d2.Invoke "Hi, Mom!"
printfn "\nA static method closed over the first argument (String)."
// The delegate must omit the first argument of the method.
// A string is passed as the firstArgument parameter, and
// the delegate is bound to this string. Use delegate type
// D3 with static method M2.
let d3 = Delegate.CreateDelegate(typeof<D3>, "Hello, World!", mi2) :?> D3
// Each time the delegate is invoked, the same string is used.
d3.Invoke()
// This code example produces the following output:
// An instance method closed over C.
// Instance method M1 on C: id = 42, s = Hello, World!
// Instance method M1 on C: id = 42, s = Hi, Mom!
//
// An open instance method.
// Instance method M1 on C: id = 42, s = Hello, World!
// Instance method M1 on C: id = 5280, s = Hi, Mom!
//
// An open static method.
// Static method M2 on C: s = Hello, World!
// Static method M2 on C: s = Hi, Mom!
//
// A static method closed over the first argument (String).
// Static method M2 on C: s = Hello, World!
Imports System.Reflection
Imports System.Security.Permissions
' Declare three delegate types for demonstrating the combinations
' of Shared versus instance methods and open versus closed
' delegates.
'
Public Delegate Sub D1(ByVal c As C, ByVal s As String)
Public Delegate Sub D2(ByVal s As String)
Public Delegate Sub D3()
' A sample class with an instance method and a Shared method.
'
Public Class C
Private id As Integer
Public Sub New(ByVal id As Integer)
Me.id = id
End Sub
Public Sub M1(ByVal s As String)
Console.WriteLine("Instance method M1 on C: id = {0}, s = {1}", _
Me.id, s)
End Sub
Public Shared Sub M2(ByVal s As String)
Console.WriteLine("Shared method M2 on C: s = {0}", s)
End Sub
End Class
Public Class Example
Public Shared Sub Main()
Dim c1 As New C(42)
' Get a MethodInfo for each method.
'
Dim mi1 As MethodInfo = GetType(C).GetMethod("M1", _
BindingFlags.Public Or BindingFlags.Instance)
Dim mi2 As MethodInfo = GetType(C).GetMethod("M2", _
BindingFlags.Public Or BindingFlags.Static)
Dim d1 As D1
Dim d2 As D2
Dim d3 As D3
Console.WriteLine(vbLf & "An instance method closed over C.")
' In this case, the delegate and the
' method must have the same list of argument types; use
' delegate type D2 with instance method M1.
'
Dim test As [Delegate] = _
[Delegate].CreateDelegate(GetType(D2), c1, mi1, False)
' Because False was specified for throwOnBindFailure
' in the call to CreateDelegate, the variable 'test'
' contains Nothing if the method fails to bind (for
' example, if mi1 happened to represent a method of
' some class other than C).
'
If test IsNot Nothing Then
d2 = CType(test, D2)
' The same instance of C is used every time the
' delegate is invoked.
d2("Hello, World!")
d2("Hi, Mom!")
End If
Console.WriteLine(vbLf & "An open instance method.")
' In this case, the delegate has one more
' argument than the instance method; this argument comes
' at the beginning, and represents the hidden instance
' argument of the instance method. Use delegate type D1
' with instance method M1.
'
d1 = CType([Delegate].CreateDelegate(GetType(D1), Nothing, mi1), D1)
' An instance of C must be passed in each time the
' delegate is invoked.
'
d1(c1, "Hello, World!")
d1(New C(5280), "Hi, Mom!")
Console.WriteLine(vbLf & "An open Shared method.")
' In this case, the delegate and the method must
' have the same list of argument types; use delegate type
' D2 with Shared method M2.
'
d2 = CType([Delegate].CreateDelegate(GetType(D2), Nothing, mi2), D2)
' No instances of C are involved, because this is a Shared
' method.
'
d2("Hello, World!")
d2("Hi, Mom!")
Console.WriteLine(vbLf & "A Shared method closed over the first argument (String).")
' The delegate must omit the first argument of the method.
' A string is passed as the firstArgument parameter, and
' the delegate is bound to this string. Use delegate type
' D3 with Shared method M2.
'
d3 = CType([Delegate].CreateDelegate(GetType(D3), "Hello, World!", mi2), D3)
' Each time the delegate is invoked, the same string is
' used.
d3()
End Sub
End Class
' This code example produces the following output:
'
'An instance method closed over C.
'Instance method M1 on C: id = 42, s = Hello, World!
'Instance method M1 on C: id = 42, s = Hi, Mom!
'
'An open instance method.
'Instance method M1 on C: id = 42, s = Hello, World!
'Instance method M1 on C: id = 5280, s = Hi, Mom!
'
'An open Shared method.
'Shared method M2 on C: s = Hello, World!
'Shared method M2 on C: s = Hi, Mom!
'
'A Shared method closed over the first argument (String).
'Shared method M2 on C: s = Hello, World!
'
Example 2
The following code example demonstrates compatibility of parameter types and return types.
The code example defines a base class named Base
and a class named Derived
that derives from Base
. The derived class has a static
(Shared
in Visual Basic) method named MyMethod
with one parameter of type Base
and a return type of Derived
. The code example also defines a delegate named Example
that has one parameter of type Derived
and a return type of Base
.
The code example demonstrates that the delegate named Example
can be used to represent the method MyMethod
. The method can be bound to the delegate because:
The parameter type of the delegate (
Derived
) is more restrictive than the parameter type ofMyMethod
(Base
), so that it is always safe to pass the argument of the delegate toMyMethod
.The return type of
MyMethod
(Derived
) is more restrictive than the parameter type of the delegate (Base
), so that it is always safe to cast the return type of the method to the return type of the delegate.
The code example produces no output.
using namespace System;
using namespace System::Reflection;
// Define two classes to use in the demonstration, a base class and
// a class that derives from it.
//
public ref class Base {};
public ref class Derived : Base
{
// Define a static method to use in the demonstration. The method
// takes an instance of Base and returns an instance of Derived.
// For the purposes of the demonstration, it is not necessary for
// the method to do anything useful.
//
public:
static Derived^ MyMethod(Base^ arg)
{
Base^ dummy = arg;
return gcnew Derived();
}
};
// Define a delegate that takes an instance of Derived and returns an
// instance of Base.
//
public delegate Base^ Example(Derived^ arg);
void main()
{
// The binding flags needed to retrieve MyMethod.
BindingFlags flags = BindingFlags::Public | BindingFlags::Static;
// Get a MethodInfo that represents MyMethod.
MethodInfo^ minfo = Derived::typeid->GetMethod("MyMethod", flags);
// Demonstrate contravariance of parameter types and covariance
// of return types by using the delegate Example to represent
// MyMethod. The delegate binds to the method because the
// parameter of the delegate is more restrictive than the
// parameter of the method (that is, the delegate accepts an
// instance of Derived, which can always be safely passed to
// a parameter of type Base), and the return type of MyMethod
// is more restrictive than the return type of Example (that
// is, the method returns an instance of Derived, which can
// always be safely cast to type Base).
//
Example^ ex =
(Example^) Delegate::CreateDelegate(Example::typeid, minfo);
// Execute MyMethod using the delegate Example.
//
Base^ b = ex(gcnew Derived());
}
using System;
using System.Reflection;
// Define two classes to use in the demonstration, a base class and
// a class that derives from it.
//
public class Base {}
public class Derived : Base
{
// Define a static method to use in the demonstration. The method
// takes an instance of Base and returns an instance of Derived.
// For the purposes of the demonstration, it is not necessary for
// the method to do anything useful.
//
public static Derived MyMethod(Base arg)
{
Base dummy = arg;
return new Derived();
}
}
// Define a delegate that takes an instance of Derived and returns an
// instance of Base.
//
public delegate Base Example(Derived arg);
class Test
{
public static void Main()
{
// The binding flags needed to retrieve MyMethod.
BindingFlags flags = BindingFlags.Public | BindingFlags.Static;
// Get a MethodInfo that represents MyMethod.
MethodInfo minfo = typeof(Derived).GetMethod("MyMethod", flags);
// Demonstrate contravariance of parameter types and covariance
// of return types by using the delegate Example to represent
// MyMethod. The delegate binds to the method because the
// parameter of the delegate is more restrictive than the
// parameter of the method (that is, the delegate accepts an
// instance of Derived, which can always be safely passed to
// a parameter of type Base), and the return type of MyMethod
// is more restrictive than the return type of Example (that
// is, the method returns an instance of Derived, which can
// always be safely cast to type Base).
//
Example ex =
(Example) Delegate.CreateDelegate(typeof(Example), minfo);
// Execute MyMethod using the delegate Example.
//
Base b = ex(new Derived());
}
}
open System
open System.Reflection
// Define two classes to use in the demonstration, a base class and
// a class that derives from it.
type Base() = class end
type Derived() =
inherit Base()
// Define a static method to use in the demonstration. The method
// takes an instance of Base and returns an instance of Derived.
// For the purposes of the demonstration, it is not necessary for
// the method to do anything useful.
static member MyMethod(arg: Base) =
Derived()
// Define a delegate that takes an instance of Derived and returns an
// instance of Base.
type Example = delegate of Derived -> Base
// The binding flags needed to retrieve MyMethod.
let flags = BindingFlags.Public ||| BindingFlags.Static
// Get a MethodInfo that represents MyMethod.
let minfo = typeof<Derived>.GetMethod("MyMethod", flags)
// Demonstrate contravariance of parameter types and covariance
// of return types by using the delegate Example to represent
// MyMethod. The delegate binds to the method because the
// parameter of the delegate is more restrictive than the
// parameter of the method (that is, the delegate accepts an
// instance of Derived, which can always be safely passed to
// a parameter of type Base), and the return type of MyMethod
// is more restrictive than the return type of Example (that
// is, the method returns an instance of Derived, which can
// always be safely cast to type Base).
let ex = Delegate.CreateDelegate(typeof<Example>, minfo) :?> Example
// Execute MyMethod using the delegate Example.
let b = Derived() |> ex.Invoke
Imports System.Reflection
' Define two classes to use in the demonstration, a base class and
' a class that derives from it.
'
Public Class Base
End Class
Public Class Derived
Inherits Base
' Define a Shared method to use in the demonstration. The method
' takes an instance of Base and returns an instance of Derived.
' For the purposes of the demonstration, it is not necessary for
' the method to do anything useful.
'
Public Shared Function MyMethod(ByVal arg As Base) As Derived
Dim dummy As Base = arg
Return New Derived()
End Function
End Class
' Define a delegate that takes an instance of Derived and returns an
' instance of Base.
'
Public Delegate Function Example(ByVal arg As Derived) As Base
Module Test
Sub Main()
' The binding flags needed to retrieve MyMethod.
Dim flags As BindingFlags = _
BindingFlags.Public Or BindingFlags.Static
' Get a MethodInfo that represents MyMethod.
Dim minfo As MethodInfo = _
GetType(Derived).GetMethod("MyMethod", flags)
' Demonstrate contravariance of parameter types and covariance
' of return types by using the delegate Example to represent
' MyMethod. The delegate binds to the method because the
' parameter of the delegate is more restrictive than the
' parameter of the method (that is, the delegate accepts an
' instance of Derived, which can always be safely passed to
' a parameter of type Base), and the return type of MyMethod
' is more restrictive than the return type of Example (that
' is, the method returns an instance of Derived, which can
' always be safely cast to type Base).
'
Dim ex As Example = CType( _
[Delegate].CreateDelegate(GetType(Example), minfo), _
Example _
)
' Execute MyMethod using the delegate Example.
'
Dim b As Base = ex(New Derived())
End Sub
End Module
Remarks
In the .NET Framework version 1.0 and 1.1, this method overload creates delegates for static methods only. In the .NET Framework version 2.0, this method overload also can create open instance method delegates; that is, delegates that explicitly supply the hidden first argument of instance methods. For a detailed explanation, see the more general CreateDelegate(Type, Object, MethodInfo) method overload, which allows you to create all combinations of open or closed delegates for instance or static methods, and optionally to specify a first argument.
Note
This method overload should be used when the delegate is not closed over its first argument, because it is somewhat faster in that case.
This method overload is equivalent to calling the CreateDelegate(Type, MethodInfo, Boolean) method overload and specifying true
for throwOnBindFailure
.
Note
Starting with the .NET Framework 2.0 Service Pack 1, this method can be used to access non-public methods if the caller has been granted ReflectionPermission with the ReflectionPermissionFlag.RestrictedMemberAccess flag and if the grant set of the non-public methods is restricted to the caller's grant set, or a subset thereof. (See Security Considerations for Reflection.)
To use this functionality, your application should target the .NET Framework 3.5 or later.
Compatible Parameter Types and Return Type
In the .NET Framework version 2.0, the parameter types and return type of a delegate created using this method overload must be compatible with the parameter types and return type of the method the delegate represents; the types do not have to match exactly. This represents a relaxation of the binding behavior in the .NET Framework version 1.0 and 1.1, where the types must match exactly.
A parameter of a delegate is compatible with the corresponding parameter of a method if the type of the delegate parameter is more restrictive than the type of the method parameter, because this guarantees that an argument passed to the delegate can be passed safely to the method.
Similarly, the return type of a delegate is compatible with the return type of a method if the return type of the method is more restrictive than the return type of the delegate, because this guarantees that the return value of the method can be cast safely to the return type of the delegate.
For example, a delegate with a parameter of type Hashtable and a return type of Object can represent a method with a parameter of type Object and a return value of type Hashtable.