Action<T1,T2,T3,T4> Delegate
Definition
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Encapsulates a method that has four parameters and does not return a value.
generic <typename T1, typename T2, typename T3, typename T4>
public delegate void Action(T1 arg1, T2 arg2, T3 arg3, T4 arg4);
public delegate void Action<in T1,in T2,in T3,in T4>(T1 arg1, T2 arg2, T3 arg3, T4 arg4);
public delegate void Action<T1,T2,T3,T4>(T1 arg1, T2 arg2, T3 arg3, T4 arg4);
type Action<'T1, 'T2, 'T3, 'T4> = delegate of 'T1 * 'T2 * 'T3 * 'T4 -> unit
Public Delegate Sub Action(Of In T1, In T2, In T3, In T4)(arg1 As T1, arg2 As T2, arg3 As T3, arg4 As T4)
Public Delegate Sub Action(Of T1, T2, T3, T4)(arg1 As T1, arg2 As T2, arg3 As T3, arg4 As T4)
Type Parameters
- T1
The type of the first parameter of the method that this delegate encapsulates.
This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.- T2
The type of the second parameter of the method that this delegate encapsulates.
This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.- T3
The type of the third parameter of the method that this delegate encapsulates.
This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.- T4
The type of the fourth parameter of the method that this delegate encapsulates.
This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.Parameters
- arg1
- T1
The first parameter of the method that this delegate encapsulates.
- arg2
- T2
The second parameter of the method that this delegate encapsulates.
- arg3
- T3
The third parameter of the method that this delegate encapsulates.
- arg4
- T4
The fourth parameter of the method that this delegate encapsulates.
Remarks
You can use the Action<T1,T2,T3,T4> delegate to pass a method as a parameter without explicitly declaring a custom delegate. The encapsulated method must correspond to the method signature that is defined by this delegate. This means that the encapsulated method must have four parameters that are all passed to it by value, and it must not return a value. (In C#, the method must return void
. In F#, the method or function must return unit. In Visual Basic, it must be defined by the Sub
…End Sub
construct. It can also be a method that returns a value that is ignored.) Typically, such a method is used to perform an operation.
Note
To reference a method that has four parameters and returns a value, use the generic Func<T1,T2,T3,T4,TResult> delegate instead.
When you use the Action<T1,T2,T3,T4> delegate, you do not have to explicitly define a delegate that encapsulates a method with four parameters. For example, the following code explicitly declares a delegate named StringCopy
and assigns a reference to the CopyStrings
method to its delegate instance.
using System;
delegate void StringCopy(string[] stringArray1,
string[] stringArray2,
int indexToStart,
int numberToCopy);
public class TestDelegate
{
public static void Main()
{
string[] ordinals = ["First", "Second", "Third", "Fourth", "Fifth",
"Sixth", "Seventh", "Eighth", "Ninth", "Tenth"];
string[] copiedOrdinals = new string[ordinals.Length];
StringCopy copyOperation = CopyStrings;
copyOperation(ordinals, copiedOrdinals, 3, 5);
Console.WriteLine();
foreach (string ordinal in copiedOrdinals)
Console.WriteLine(string.IsNullOrEmpty(ordinal) ? "<None>" : ordinal);
}
private static void CopyStrings(string[] source, string[] target,
int startPos, int number)
{
if (source.Length != target.Length)
throw new IndexOutOfRangeException("The source and target arrays must have the same number of elements.");
for (int ctr = startPos; ctr <= startPos + number - 1; ctr++)
target[ctr] = source[ctr];
}
}
open System
type StringCopy = delegate of stringArray1: string [] *
stringArray2: string [] *
indexToStart: int *
numberToCopy: int -> unit
let copyStrings (source: string []) (target: string []) startPos number =
if source.Length <> target.Length then
raise (IndexOutOfRangeException "The source and target arrays must have the same number of elements.")
for i = startPos to startPos + number - 1 do
target.[i] <- source.[i]
let ordinals =
[| "First"; "Second"; "Third"; "Fourth"; "Fifth"
"Sixth"; "Seventh"; "Eighth"; "Ninth"; "Tenth" |]
let copiedOrdinals: string [] = Array.zeroCreate ordinals.Length
let copyOperation = StringCopy copyStrings
copyOperation.Invoke(ordinals, copiedOrdinals, 3, 5)
for ordinal in copiedOrdinals do
printfn "%s" (if String.IsNullOrEmpty ordinal then "<None>" else ordinal)
Delegate Sub StringCopy(stringArray1() As String, _
stringArray2() As String, _
indexToStart As Integer, _
numberToCopy As Integer)
Module TestDelegate
Public Sub RunIt()
Dim ordinals() As String = {"First", "Second", "Third", "Fourth",
"Fifth", "Sixth", "Seventh", "Eighth",
"Ninth", "Tenth"}
Dim copiedOrdinals(ordinals.Length - 1) As String
Dim copyOperation As StringCopy = AddressOf CopyStrings
copyOperation(ordinals, copiedOrdinals, 3, 5)
Console.WriteLine()
For Each ordinal As String In copiedOrdinals
If String.IsNullOrEmpty(ordinal) Then
Console.WriteLine("<None>")
Else
Console.WriteLine(ordinal)
End If
Next
End Sub
Private Sub CopyStrings(source() As String, target() As String, _
startPos As Integer, number As Integer)
If source.Length <> target.Length Then
Throw New IndexOutOfRangeException("The source and target arrays" & _
" must have the same number of elements.")
End If
For ctr As Integer = startPos to startpos + number - 1
target(ctr) = source(ctr)
Next
End Sub
End Module
The following example simplifies this code by instantiating the Action<T1,T2,T3,T4> delegate instead of explicitly defining a new delegate and assigning a named method to it.
using System;
public class TestAction4
{
public static void Main()
{
string[] ordinals = ["First", "Second", "Third", "Fourth", "Fifth",
"Sixth", "Seventh", "Eighth", "Ninth", "Tenth"];
string[] copiedOrdinals = new string[ordinals.Length];
Action<string[], string[], int, int> copyOperation = CopyStrings;
copyOperation(ordinals, copiedOrdinals, 3, 5);
Console.WriteLine();
foreach (string ordinal in copiedOrdinals)
Console.WriteLine(string.IsNullOrEmpty(ordinal) ? "<None>" : ordinal);
}
private static void CopyStrings(string[] source, string[] target,
int startPos, int number)
{
if (source.Length != target.Length)
throw new IndexOutOfRangeException("The source and target arrays must have the same number of elements.");
for (int ctr = startPos; ctr <= startPos + number - 1; ctr++)
target[ctr] = source[ctr];
}
}
open System
let copyStrings (source: string []) (target: string []) startPos number =
if source.Length <> target.Length then
raise (IndexOutOfRangeException "The source and target arrays must have the same number of elements.")
for i = startPos to startPos + number - 1 do
target.[i] <- source.[i]
let ordinals =
[| "First"; "Second"; "Third"; "Fourth"; "Fifth"
"Sixth"; "Seventh"; "Eighth"; "Ninth"; "Tenth" |]
let copiedOrdinals: string [] = Array.zeroCreate ordinals.Length
let copyOperation = Action<_, _, _, _> copyStrings
copyOperation.Invoke(ordinals, copiedOrdinals, 3, 5)
for ordinal in copiedOrdinals do
printfn "%s" (if String.IsNullOrEmpty ordinal then "<None>" else ordinal)
Module TestAction4
Public Sub RunIt()
Dim ordinals() As String = {"First", "Second", "Third", "Fourth",
"Fifth", "Sixth", "Seventh", "Eighth",
"Ninth", "Tenth"}
Dim copiedOrdinals(ordinals.Length - 1) As String
Dim copyOperation As Action(Of String(), String(), Integer, Integer) =
AddressOf CopyStrings
copyOperation(ordinals, copiedOrdinals, 3, 5)
Console.WriteLine()
For Each ordinal As String In copiedOrdinals
If String.IsNullOrEmpty(ordinal) Then
Console.WriteLine("<None>")
Else
Console.WriteLine(ordinal)
End If
Next
End Sub
Private Sub CopyStrings(source() As String, target() As String, _
startPos As Integer, number As Integer)
If source.Length <> target.Length Then
Throw New IndexOutOfRangeException("The source and target arrays" & _
" must have the same number of elements.")
End If
For ctr As Integer = startPos to startpos + number - 1
target(ctr) = source(ctr)
Next
End Sub
End Module
You can also use the Action<T1,T2,T3,T4> delegate with anonymous methods in C#, as the following example illustrates. (For an introduction to anonymous methods, see Anonymous Methods.)
using System;
public class TestAnonymousMethod
{
public static void Main()
{
string[] ordinals = ["First", "Second", "Third", "Fourth", "Fifth",
"Sixth", "Seventh", "Eighth", "Ninth", "Tenth"];
string[] copiedOrdinals = new string[ordinals.Length];
Action<string[], string[], int, int> copyOperation =
delegate (string[] s1, string[] s2,
int pos, int num)
{ CopyStrings(s1, s2, pos, num); };
copyOperation(ordinals, copiedOrdinals, 3, 5);
Console.WriteLine();
foreach (string ordinal in copiedOrdinals)
Console.WriteLine(string.IsNullOrEmpty(ordinal) ? "<None>" : ordinal);
}
private static void CopyStrings(string[] source, string[] target,
int startPos, int number)
{
if (source.Length != target.Length)
throw new IndexOutOfRangeException("The source and target arrays must have the same number of elements.");
for (int ctr = startPos; ctr <= startPos + number - 1; ctr++)
target[ctr] = source[ctr];
}
}
You can also assign a lambda expression to an Action<T1,T2,T3,T4> delegate instance, as the following example illustrates. (For an introduction to lambda expressions, see Lambda Expressions (C#) or Lambda Expressions (F#).)
using System;
public class TestLambdaExpression
{
public static void Main()
{
string[] ordinals = ["First", "Second", "Third", "Fourth", "Fifth",
"Sixth", "Seventh", "Eighth", "Ninth", "Tenth"];
string[] copiedOrdinals = new string[ordinals.Length];
Action<string[], string[], int, int> copyOperation = (s1, s2, pos, num)
=> CopyStrings(s1, s2, pos, num);
copyOperation(ordinals, copiedOrdinals, 3, 5);
Console.WriteLine();
foreach (string ordinal in copiedOrdinals)
Console.WriteLine(string.IsNullOrEmpty(ordinal) ? "<None>" : ordinal);
}
private static void CopyStrings(string[] source, string[] target,
int startPos, int number)
{
if (source.Length != target.Length)
throw new IndexOutOfRangeException("The source and target arrays must have the same number of elements.");
for (int ctr = startPos; ctr <= startPos + number - 1; ctr++)
target[ctr] = source[ctr];
}
}
open System
let copyStrings (source: string []) (target: string []) startPos number =
if source.Length <> target.Length then
raise (IndexOutOfRangeException "The source and target arrays must have the same number of elements.")
for i = startPos to startPos + number - 1 do
target.[i] <- source.[i]
let ordinals =
[| "First"; "Second"; "Third"; "Fourth"; "Fifth"
"Sixth"; "Seventh"; "Eighth"; "Ninth"; "Tenth" |]
let copiedOrdinals: string [] = Array.zeroCreate ordinals.Length
let copyOperation = Action<_, _, _, _> (fun s1 s2 pos num -> copyStrings s1 s2 pos num)
copyOperation.Invoke(ordinals, copiedOrdinals, 3, 5)
for ordinal in copiedOrdinals do
printfn "%s" (if String.IsNullOrEmpty ordinal then "<None>" else ordinal)
Public Module TestLambdaExpression
Public Sub RunIt()
Dim ordinals() As String = {"First", "Second", "Third", "Fourth", "Fifth",
"Sixth", "Seventh", "Eighth", "Ninth", "Tenth"}
Dim copiedOrdinals(ordinals.Length - 1) As String
Dim copyOperation As Action(Of String(), String(), Integer, Integer) =
Sub(s1, s2, pos, num) CopyStrings(s1, s2, pos, num)
copyOperation(ordinals, copiedOrdinals, 3, 5)
Console.WriteLine()
For Each ordinal As String In copiedOrdinals
If String.IsNullOrEmpty(ordinal) Then
Console.WriteLine("<None>")
Else
Console.WriteLine(ordinal)
End If
Next
End Sub
Private Function CopyStrings(source() As String, target() As String,
startPos As Integer, number As Integer) As Integer
If source.Length <> target.Length Then
Throw New IndexOutOfRangeException("The source and target arrays must have the same number of elements.")
End If
For ctr As Integer = startPos To startPos + number - 1
target(ctr) = source(ctr)
Next
Return number
End Function
End Module
' The example displays the following output:
' Fourth
' Fifth
' Sixth
' Seventh
' Eighth
Extension Methods
GetMethodInfo(Delegate) |
Gets an object that represents the method represented by the specified delegate. |
Applies to
See also
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