MulticastDelegate Class
Definition
Important
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Represents a multicast delegate; that is, a delegate that can have more than one element in its invocation list.
public ref class MulticastDelegate abstract : Delegate
public abstract class MulticastDelegate : Delegate
[System.Serializable]
public abstract class MulticastDelegate : Delegate
[System.Serializable]
[System.Runtime.InteropServices.ComVisible(true)]
public abstract class MulticastDelegate : Delegate
type MulticastDelegate = class
inherit Delegate
[<System.Serializable>]
type MulticastDelegate = class
inherit Delegate
[<System.Serializable>]
[<System.Runtime.InteropServices.ComVisible(true)>]
type MulticastDelegate = class
inherit Delegate
Public MustInherit Class MulticastDelegate
Inherits Delegate
- Inheritance
- Attributes
Examples
The following example defines a class, StringContainer
, which includes a collection of strings. One of its members is the CheckAndDisplayDelegate
delegate, which is used to display strings stored in a StringContainer
object that satisfy particular criteria. The delegate takes a single string as a parameter and returns void
(or, in Visual Basic, it's a Sub
procedure). It also includes a method, DisplayAllQualified
, that has a single parameter, a CheckAndDisplayDelegate
delegate. This allows the method to be called and to display a set of strings that are filtered based on the methods that the delegate contains.
The example also defines a utility class, StringExtensions
, that has two methods:
ConStart
, which displays strings that begin with a consonant.VowelStart
, which displays strings that begin with a vowel.
Note that both methods include a single string parameter and return void
. In other words, both methods can be assigned to the CheckAndDisplayDelegate
delegate.
The Test.Main
method is the application entry point. It instantiates a StringContainer
object, populates it with strings, and creates two CheckAndDisplayDelegate
delegates, conStart
and vowelStart
, that invoke a single method. It then calls the Delegate.Combine method to create the multipleDelegates
delegate, which initially contains the ConStart
and VowelStart
delegates. Note that when the multipleDelegates
delegate is invoked, it displays all the strings in the collection in their original order. This is because each letter is passed separately to each delegate, and each letter meets the filtering criteria of only one of the two delegates. Finally, after calls to Delegate.Remove and Delegate.Combine, multipleDelegates
contains two conStart
delegates. When it is invoked, each string in the StringContainer
object is displayed twice.
using namespace System;
using namespace System::Collections::Generic;
ref class StringContainer
{
private:
// A generic list object that holds the strings.
List<String^>^ container = gcnew List<String^>;
public:
// Define a delegate to handle string display.
delegate void CheckAndDisplayDelegate(String^ str);
// A method that adds more strings to the collection.
void AddString(String^ str)
{
container->Add(str);
}
// Iterate through the strings and invoke the method(s) that the delegate points to.
void DisplayAllQualified(CheckAndDisplayDelegate^ displayDelegate)
{
for each (String^ str in container)
displayDelegate(str);
// System::Collections::IEnumerator^ myEnum = container->GetEnumerator();
// while ( myEnum->MoveNext() )
// {
// String^ str = safe_cast<String^>(myEnum->Current);
// displayDelegate(str);
// }
}
};
//end of class StringContainer
// This class contains a few sample methods
ref class StringFuncs
{
public:
// This method prints a String* that it is passed if the String* starts with a vowel
static void ConStart(String^ str)
{
if ( !(str[ 0 ] == 'a' || str[ 0 ] == 'e' || str[ 0 ] == 'i' || str[ 0 ] == 'o' || str[ 0 ] == 'u') )
Console::WriteLine( str );
}
// This method prints a String* that it is passed if the String* starts with a consonant
static void VowelStart( String^ str )
{
if ( (str[ 0 ] == 'a' || str[ 0 ] == 'e' || str[ 0 ] == 'i' || str[ 0 ] == 'o' || str[ 0 ] == 'u') )
Console::WriteLine( str );
}
};
// This function demonstrates using Delegates, including using the Remove and
// Combine methods to create and modify delegate combinations.
int main()
{
// Declare the StringContainer class and add some strings
StringContainer^ container = gcnew StringContainer;
container->AddString( "This" );
container->AddString( "is" );
container->AddString( "a" );
container->AddString( "multicast" );
container->AddString( "delegate" );
container->AddString( "example" );
// RETURN HERE.
// Create two delegates individually using different methods
StringContainer::CheckAndDisplayDelegate^ conStart = gcnew StringContainer::CheckAndDisplayDelegate( StringFuncs::ConStart );
StringContainer::CheckAndDisplayDelegate^ vowelStart = gcnew StringContainer::CheckAndDisplayDelegate( StringFuncs::VowelStart );
// Get the list of all delegates assigned to this MulticastDelegate instance.
array<Delegate^>^ delegateList = conStart->GetInvocationList();
Console::WriteLine("conStart contains {0} delegate(s).", delegateList->Length);
delegateList = vowelStart->GetInvocationList();
Console::WriteLine("vowelStart contains {0} delegate(s).\n", delegateList->Length );
// Determine whether the delegates are System::Multicast delegates
if ( dynamic_cast<System::MulticastDelegate^>(conStart) && dynamic_cast<System::MulticastDelegate^>(vowelStart) )
{
Console::WriteLine("conStart and vowelStart are derived from MulticastDelegate.\n");
}
// Execute the two delegates.
Console::WriteLine("Executing the conStart delegate:" );
container->DisplayAllQualified(conStart);
Console::WriteLine();
Console::WriteLine("Executing the vowelStart delegate:" );
container->DisplayAllQualified(vowelStart);
// Create a new MulticastDelegate and call Combine to add two delegates.
StringContainer::CheckAndDisplayDelegate^ multipleDelegates =
dynamic_cast<StringContainer::CheckAndDisplayDelegate^>(Delegate::Combine(conStart, vowelStart));
// How many delegates does multipleDelegates contain?
delegateList = multipleDelegates->GetInvocationList();
Console::WriteLine("\nmultipleDelegates contains {0} delegates.\n",
delegateList->Length );
// // Pass this multicast delegate to DisplayAllQualified.
Console::WriteLine("Executing the multipleDelegate delegate.");
container->DisplayAllQualified(multipleDelegates);
// Call remove and combine to change the contained delegates.
multipleDelegates = dynamic_cast<StringContainer::CheckAndDisplayDelegate^>
(Delegate::Remove(multipleDelegates, vowelStart));
multipleDelegates = dynamic_cast<StringContainer::CheckAndDisplayDelegate^>
(Delegate::Combine(multipleDelegates, conStart));
// Pass multipleDelegates to DisplayAllQualified again.
Console::WriteLine("\nExecuting the multipleDelegate delegate with two conStart delegates:");
container->DisplayAllQualified(multipleDelegates);
}
// The example displays the following output:
// conStart contains 1 delegate(s).
// vowelStart contains 1 delegate(s).
//
// conStart and vowelStart are derived from MulticastDelegate.
//
// Executing the conStart delegate:
// This
// multicast
// delegate
//
// Executing the vowelStart delegate:
// is
// a
// example
//
//
// multipleDelegates contains 2 delegates.
//
// Executing the multipleDelegate delegate.
// This
// is
// a
// multicast
// delegate
// example
//
// Executing the multipleDelegate delegate with two conStart delegates:
// This
// This
// multicast
// multicast
// delegate
// delegate
using System;
using System.Collections.Generic;
class StringContainer
{
// Define a delegate to handle string display.
public delegate void CheckAndDisplayDelegate(string str);
// A generic list object that holds the strings.
private List<String> container = new List<String>();
// A method that adds strings to the collection.
public void AddString(string str)
{
container.Add(str);
}
// Iterate through the strings and invoke the method(s) that the delegate points to.
public void DisplayAllQualified(CheckAndDisplayDelegate displayDelegate)
{
foreach (var str in container) {
displayDelegate(str);
}
}
}
// This class defines some methods to display strings.
class StringExtensions
{
// Display a string if it starts with a consonant.
public static void ConStart(string str)
{
if (!(str[0]=='a'||str[0]=='e'||str[0]=='i'||str[0]=='o'||str[0]=='u'))
Console.WriteLine(str);
}
// Display a string if it starts with a vowel.
public static void VowelStart(string str)
{
if ((str[0]=='a'||str[0]=='e'||str[0]=='i'||str[0]=='o'||str[0]=='u'))
Console.WriteLine(str);
}
}
// Demonstrate the use of delegates, including the Remove and
// Combine methods to create and modify delegate combinations.
class Test
{
static public void Main()
{
// Declare the StringContainer class and add some strings
StringContainer container = new StringContainer();
container.AddString("This");
container.AddString("is");
container.AddString("a");
container.AddString("multicast");
container.AddString("delegate");
container.AddString("example");
// Create two delegates individually using different methods.
StringContainer.CheckAndDisplayDelegate conStart = StringExtensions.ConStart;
StringContainer.CheckAndDisplayDelegate vowelStart = StringExtensions.VowelStart;
// Get the list of all delegates assigned to this MulticastDelegate instance.
Delegate[] delegateList = conStart.GetInvocationList();
Console.WriteLine("conStart contains {0} delegate(s).", delegateList.Length);
delegateList = vowelStart.GetInvocationList();
Console.WriteLine("vowelStart contains {0} delegate(s).\n", delegateList.Length);
// Determine whether the delegates are System.Multicast delegates.
if (conStart is System.MulticastDelegate && vowelStart is System.MulticastDelegate)
Console.WriteLine("conStart and vowelStart are derived from MulticastDelegate.\n");
// Execute the two delegates.
Console.WriteLine("Executing the conStart delegate:");
container.DisplayAllQualified(conStart);
Console.WriteLine();
Console.WriteLine("Executing the vowelStart delegate:");
container.DisplayAllQualified(vowelStart);
Console.WriteLine();
// Create a new MulticastDelegate and call Combine to add two delegates.
StringContainer.CheckAndDisplayDelegate multipleDelegates =
(StringContainer.CheckAndDisplayDelegate) Delegate.Combine(conStart, vowelStart);
// How many delegates does multipleDelegates contain?
delegateList = multipleDelegates.GetInvocationList();
Console.WriteLine("\nmultipleDelegates contains {0} delegates.\n",
delegateList.Length);
// Pass this multicast delegate to DisplayAllQualified.
Console.WriteLine("Executing the multipleDelegate delegate.");
container.DisplayAllQualified(multipleDelegates);
// Call remove and combine to change the contained delegates.
multipleDelegates = (StringContainer.CheckAndDisplayDelegate) Delegate.Remove(multipleDelegates, vowelStart);
multipleDelegates = (StringContainer.CheckAndDisplayDelegate) Delegate.Combine(multipleDelegates, conStart);
// Pass multipleDelegates to DisplayAllQualified again.
Console.WriteLine("\nExecuting the multipleDelegate delegate with two conStart delegates:");
container.DisplayAllQualified(multipleDelegates);
}
}
// The example displays the following output:
// conStart contains 1 delegate(s).
// vowelStart contains 1 delegate(s).
//
// conStart and vowelStart are derived from MulticastDelegate.
//
// Executing the conStart delegate:
// This
// multicast
// delegate
//
// Executing the vowelStart delegate:
// is
// a
// example
//
//
// multipleDelegates contains 2 delegates.
//
// Executing the multipleDelegate delegate.
// This
// is
// a
// multicast
// delegate
// example
//
// Executing the multipleDelegate delegate with two conStart delegates:
// This
// This
// multicast
// multicast
// delegate
// delegate
module Test
open System
// Define a delegate to handle string display.
type CheckAndDisplayDelegate = delegate of string -> unit
type StringContainer() =
// A generic ResizeArray object that holds the strings.
let container = ResizeArray()
// A method that adds strings to the collection.
member _.AddString(str) =
container.Add str
// Iterate through the strings and invoke the method(s) that the delegate points to.
member _.DisplayAllQualified(displayDelegate: CheckAndDisplayDelegate) =
for str in container do
displayDelegate.Invoke str
// This module defines some functions to display strings.
module StringExtensions =
// Display a string if it starts with a consonant.
let conStart (str: string) =
match str[0] with
| 'a' | 'e' | 'i' | 'o' | 'u' -> ()
| _ -> printfn $"{str}"
// Display a string if it starts with a vowel.
let vowelStart (str: string) =
match str[0] with
| 'a' | 'e' | 'i' | 'o' | 'u' -> printfn $"{str}"
| _ -> ()
// Demonstrate the use of delegates, including the Remove and
// Combine methods to create and modify delegate combinations.
[<EntryPoint>]
let main _ =
// Declare the StringContainer class and add some strings
let container = StringContainer()
container.AddString "This"
container.AddString "is"
container.AddString "a"
container.AddString "multicast"
container.AddString "delegate"
container.AddString "example"
// Create two delegates individually using different methods.
let conStart = CheckAndDisplayDelegate StringExtensions.conStart
let vowelStart = CheckAndDisplayDelegate StringExtensions.vowelStart
// Get the list of all delegates assigned to this MulticastDelegate instance.
let delegateList = conStart.GetInvocationList()
printfn $"conStart contains {delegateList.Length} delegate(s)."
let delegateList = vowelStart.GetInvocationList()
printfn $"vowelStart contains {delegateList.Length} delegate(s).\n"
// Determine whether the delegates are System.Multicast delegates.
if box conStart :? System.MulticastDelegate && box vowelStart :? System.MulticastDelegate then
printfn "conStart and vowelStart are derived from MulticastDelegate.\n"
// Execute the two delegates.
printfn "Executing the conStart delegate:"
container.DisplayAllQualified conStart
printfn "\nExecuting the vowelStart delegate:"
container.DisplayAllQualified vowelStart
printfn ""
// Create a new MulticastDelegate and call Combine to add two delegates.
let multipleDelegates =
Delegate.Combine(conStart, vowelStart) :?> CheckAndDisplayDelegate
// How many delegates does multipleDelegates contain?
let delegateList = multipleDelegates.GetInvocationList()
printfn $"\nmultipleDelegates contains {delegateList.Length} delegates.\n"
// Pass this multicast delegate to DisplayAllQualified.
printfn "Executing the multipleDelegate delegate."
container.DisplayAllQualified multipleDelegates
// Call remove and combine to change the contained delegates.
let multipleDelegates = Delegate.Remove(multipleDelegates, vowelStart) :?> CheckAndDisplayDelegate
let multipleDelegates = Delegate.Combine(multipleDelegates, conStart) :?> CheckAndDisplayDelegate
// Pass multipleDelegates to DisplayAllQualified again.
printfn "\nExecuting the multipleDelegate delegate with two conStart delegates:"
printfn $"{multipleDelegates}"
0
// The example displays the following output:
// conStart contains 1 delegate(s).
// vowelStart contains 1 delegate(s).
//
// conStart and vowelStart are derived from MulticastDelegate.
//
// Executing the conStart delegate:
// This
// multicast
// delegate
//
// Executing the vowelStart delegate:
// is
// a
// example
//
//
// multipleDelegates contains 2 delegates.
//
// Executing the multipleDelegate delegate.
// This
// is
// a
// multicast
// delegate
// example
//
// Executing the multipleDelegate delegate with two conStart delegates:
// This
// This
// multicast
// multicast
// delegate
// delegate
Imports System.Collections.Generic
Class StringContainer
' Define a delegate to handle string display.
Delegate Sub CheckAndPrintDelegate(ByVal str As String)
' A generic list object that holds the strings.
Private container As New List(Of String)()
' A method that adds strings to the collection.
Public Sub AddString(ByVal s As String)
container.Add(s)
End Sub
' Iterate through the strings and invoke the method(s) that the delegate points to.
Public Sub DisplayAllQualified(ByVal displayDelegate As CheckAndPrintDelegate)
For Each s In container
displayDelegate(s)
Next
End Sub
End Class
' This class defines some methods to display strings.
Class StringExtensions
' Display a string if it starts with a consonant.
Public Shared Sub ConStart(ByVal str As String)
If Not (str.Chars(0) = "a"c Or str.Chars(0) = "e"c Or str.Chars(0) = "i"c _
Or str.Chars(0) = "o"c Or str.Chars(0) = "u"c) Then
Console.WriteLine(str)
End If
End Sub
' Display a string if it starts with a vowel.
Public Shared Sub VowelStart(ByVal str As String)
If (str.Chars(0) = "a"c Or str.Chars(0) = "e"c Or str.Chars(0) = "i"c _
Or str.Chars(0) = "o"c Or str.Chars(0) = "u"c) Then
Console.WriteLine(str)
End If
End Sub
End Class
' Demonstrate the use of delegates, including the Remove and
' Combine methods to create and modify delegate combinations.
Class Test
Public Shared Sub Main()
' Declare the StringContainer class and add some strings
Dim container As New StringContainer()
container.AddString("this")
container.AddString("is")
container.AddString("a")
container.AddString("multicast")
container.AddString("delegate")
container.AddString("example")
' Create two delegates individually using different methods.
Dim constart As StringContainer.CheckAndPrintDelegate = AddressOf StringExtensions.ConStart
Dim vowelStart As StringContainer.CheckAndPrintDelegate = AddressOf StringExtensions.VowelStart
' Get the list of all delegates assigned to this MulticastDelegate instance.
Dim delegateList() As [Delegate] = conStart.GetInvocationList()
Console.WriteLine("conStart contains {0} delegate(s).", delegateList.Length)
delegateList = vowelStart.GetInvocationList()
Console.WriteLine("vowelStart contains {0} delegate(s).", delegateList.Length)
Console.WriteLine()
' Determine whether the delegates are System.Multicast delegates
If TypeOf conStart Is System.MulticastDelegate And TypeOf vowelStart Is System.MulticastDelegate Then
Console.WriteLine("conStart and vowelStart are derived from MulticastDelegate.")
Console.WriteLine()
End If
' Run the two single delegates one after the other.
Console.WriteLine("Executing the conStart delegate:")
container.DisplayAllQualified(conStart)
Console.WriteLine("Executing the vowelStart delegate:")
container.DisplayAllQualified(vowelStart)
Console.WriteLine()
' Create a new MulticastDelegate and call Combine to add two delegates.
Dim multipleDelegates As StringContainer.CheckAndPrintDelegate =
CType([Delegate].Combine(conStart, vowelStart),
StringContainer.CheckAndPrintDelegate)
' How many delegates does multipleDelegates contain?
delegateList = multipleDelegates.GetInvocationList()
Console.WriteLine("{1}multipleDelegates contains {0} delegates.{1}",
delegateList.Length, vbCrLf)
' Pass this mulitcast delegate to DisplayAllQualified.
Console.WriteLine("Executing the multipleDelegate delegate.")
container.DisplayAllQualified(multipleDelegates)
' Call remove and combine to change the contained delegates.
multipleDelegates = CType([Delegate].Remove(multipleDelegates, vowelStart),
StringContainer.CheckAndPrintDelegate)
multipleDelegates = CType([Delegate].Combine(multipleDelegates, conStart),
StringContainer.CheckAndPrintDelegate)
' Pass multipleDelegates to DisplayAllQualified again.
Console.WriteLine()
Console.WriteLine("Executing the multipleDelegate delegate with two conStart delegates:")
container.DisplayAllQualified(multipleDelegates)
End Sub
End Class
' The example displays the following output:
' conStart contains 1 delegate(s).
' vowelStart contains 1 delegate(s).
'
' conStart and vowelStart are derived from MulticastDelegate.
'
' Executing the conStart delegate:
' This
' multicast
' delegate
'
' Executing the vowelStart delegate:
' is
' a
' example
'
'
' multipleDelegates contains 2 delegates.
'
' Executing the multipleDelegate delegate.
' This
' is
' a
' multicast
' delegate
' example
'
' Executing the multipleDelegate delegate with two conStart delegates:
' This
' This
' multicast
' multicast
' delegate
' delegate
Remarks
MulticastDelegate is a special class. Compilers and other tools can derive from this class, but you cannot derive from it explicitly. The same is true of the Delegate class.
In addition to the methods that delegate types inherit from MulticastDelegate, the common language runtime provides two special methods: BeginInvoke
and EndInvoke
. For more information about these methods, see Calling Synchronous Methods Asynchronously.
A MulticastDelegate has a linked list of delegates, called an invocation list, consisting of one or more elements. When a multicast delegate is invoked, the delegates in the invocation list are called synchronously in the order in which they appear. If an error occurs during execution of the list then an exception is thrown.
Constructors
MulticastDelegate(Object, String) |
Initializes a new instance of the MulticastDelegate class. |
MulticastDelegate(Type, String) |
Initializes a new instance of the MulticastDelegate class. |
Properties
HasSingleTarget |
Gets a value that indicates whether the Delegate has a single invocation target. (Inherited from Delegate) |
Method |
Gets the method represented by the delegate. (Inherited from Delegate) |
Target |
Gets the class instance on which the current delegate invokes the instance method. (Inherited from Delegate) |
Methods
Clone() |
Creates a shallow copy of the delegate. (Inherited from Delegate) |
CombineImpl(Delegate) |
Combines this Delegate with the specified Delegate to form a new delegate. |
CombineImpl(Delegate) |
Concatenates the invocation lists of the specified multicast (combinable) delegate and the current multicast (combinable) delegate. (Inherited from Delegate) |
DynamicInvoke(Object[]) |
Dynamically invokes (late-bound) the method represented by the current delegate. (Inherited from Delegate) |
DynamicInvokeImpl(Object[]) |
Processes the full invocation list. |
DynamicInvokeImpl(Object[]) |
Dynamically invokes (late-bound) the method represented by the current delegate. (Inherited from Delegate) |
Equals(Object) |
Determines whether this multicast delegate and the specified object are equal. |
GetHashCode() |
Returns the hash code for this instance. |
GetInvocationList() |
Returns the invocation list of this multicast delegate, in invocation order. |
GetMethodImpl() |
Returns a method represented by the current MulticastDelegate. |
GetMethodImpl() |
Gets the method represented by the current delegate. (Inherited from Delegate) |
GetObjectData(SerializationInfo, StreamingContext) |
Obsolete.
Populates a SerializationInfo object with all the data needed to serialize this instance. |
GetObjectData(SerializationInfo, StreamingContext) |
Obsolete.
Not supported. (Inherited from Delegate) |
GetType() |
Gets the Type of the current instance. (Inherited from Object) |
MemberwiseClone() |
Creates a shallow copy of the current Object. (Inherited from Object) |
RemoveImpl(Delegate) |
Removes an element from the invocation list of this MulticastDelegate that is equal to the specified delegate. |
RemoveImpl(Delegate) |
Removes the invocation list of a delegate from the invocation list of another delegate. (Inherited from Delegate) |
ToString() |
Returns a string that represents the current object. (Inherited from Object) |
Operators
Equality(MulticastDelegate, MulticastDelegate) |
Determines whether two MulticastDelegate objects are equal. |
Inequality(MulticastDelegate, MulticastDelegate) |
Determines whether two MulticastDelegate objects are not equal. |
Extension Methods
GetMethodInfo(Delegate) |
Gets an object that represents the method represented by the specified delegate. |
Applies to
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