Action(Of T1, T2, T3, T4) Delegate
Updated: February 2009
Encapsulates a method that has four parameters and does not return a value.
Assembly: System.Core (in System.Core.dll)
'Declaration Public Delegate Sub Action(Of T1, T2, T3, T4) ( _ arg1 As T1, _ arg2 As T2, _ arg3 As T3, _ arg4 As T4 _ ) 'Usage Dim instance As New Action(Of T1, T2, T3, T4)(AddressOf HandlerMethod)
Type Parameters
- T1
The type of the first parameter of the method that this delegate encapsulates.
- T2
The type of the second parameter of the method that this delegate encapsulates.
- T3
The type of the third parameter of the method that this delegate encapsulates.
- T4
The type of the fourth parameter of the method that this delegate encapsulates.
Parameters
- arg1
- Type: T1
The first parameter of the method that this delegate encapsulates.
- arg2
- Type: T2
The second parameter of the method that this delegate encapsulates.
- arg3
- Type: T3
The third parameter of the method that this delegate encapsulates.
- arg4
- Type: T4
The fourth parameter of the method that this delegate encapsulates.
You can use the Action(Of 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 Visual Basic, it must be defined by the Sub…End Sub construct.) Typically, such a method is used to perform an operation.
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To reference a method that has four parameters and returns a value, use the generic Func(Of T1, T2, T3, T4, TResult) delegate instead. |
When you use the Action(Of 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.
Delegate Sub StringCopy(stringArray1() As String, _ stringArray2() As String, _ indexToStart As Integer, _ numberToCopy As Integer) Module TestDelegate Public Sub Main() 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) For Each ordinal As String In copiedOrdinals Console.WriteLine(ordinal) 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) = String.Copy(source(ctr)) Next End Sub End Module
The following example simplifies this code by instantiating the Action(Of T1, T2, T3) delegate rather than explicitly defining a new delegate and assigning a named method to it.
Module TestAction4 Public Sub Main() 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) For Each ordinal As String In copiedOrdinals Console.WriteLine(ordinal) 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) = String.Copy(source(ctr)) Next End Sub End Module
You can also use the Action(Of T1, T2, T3, T4) delegate with anonymous methods in C#, as the following example illustrates. (For an introduction to anonymous methods, see Anonymous Methods (C# Programming Guide).)
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); 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] = String.Copy(source[ctr]); } }
You can also assign a lambda expression to an Action(Of T1, T2, T3, T4) delegate instance, as the following example illustrates. (For an introduction to lambda expressions, see Lambda Expressions (C# Programming Guide).)
Public Module TestLambdaExpression Public Sub Main() 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) = _ Function(s1, s2, pos, num) CopyStrings(s1, s2, pos, num) copyOperation(ordinals, copiedOrdinals, 3, 5) 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) = String.Copy(source(ctr)) Next Return number End Function End Module ' The example displays the following output: ' <None> ' <None> ' <None> ' Fourth ' Fifth ' Sixth ' Seventh ' Eighth ' <None> ' <None>
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Visual Basic requires that a lambda expression return a value. As a result, that return value must be discarded if the lambda expression is to be used with the Action(Of T1, T2, T3, T4) delegate. |
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The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
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