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Action Delegate

Encapsulates a method that has no parameters and does not return a value.

Namespace:  System
Assemblies:   mscorlib (in mscorlib.dll)
  System.Runtime (in System.Runtime.dll)

'Declaration
Public Delegate Sub Action

The Action type exposes the following members.

  NameDescription
Public methodSupported in .NET for Windows Store appsAction
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  NameDescription
Public propertySupported in .NET for Windows Store appsTargetGets the class instance on which the current delegate invokes the instance method. (Inherited from Delegate.)
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  NameDescription
Public methodSupported in .NET for Windows Store appsBeginInvoke
Public methodSupported in .NET for Windows Store appsDynamicInvokeDynamically invokes (late-bound) the method represented by the current delegate. (Inherited from Delegate.)
Public methodSupported in .NET for Windows Store appsEndInvoke
Public methodSupported in .NET for Windows Store appsEqualsDetermines whether this multicast delegate and the specified object are equal. (Inherited from MulticastDelegate.)
Public methodSupported in .NET for Windows Store appsGetHashCodeReturns the hash code for this instance. (Inherited from MulticastDelegate.)
Public methodSupported in .NET for Windows Store appsGetInvocationListReturns the invocation list of this multicast delegate, in invocation order. (Inherited from MulticastDelegate.)
Public methodSupported in .NET for Windows Store appsGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodSupported in .NET for Windows Store appsInvoke
Public methodSupported in .NET for Windows Store appsToStringReturns a string that represents the current object. (Inherited from Object.)
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  NameDescription
Public Extension MethodSupported in .NET for Windows Store appsGetMethodInfoGets an object that represents the method represented by the specified delegate. (Defined by RuntimeReflectionExtensions.)
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You can use this 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 no parameters and no return value. (In C#, the method must return void. In Visual Basic, it must be defined by the SubEnd 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.

NoteNote

To reference a method that has no parameters and returns a value, use the generic Func(Of TResult) delegate instead.

When you use the Action delegate, you do not have to explicitly define a delegate that encapsulates a parameterless procedure. For example, the following code explicitly declares a delegate named ShowValue and assigns a reference to the Name.DisplayToWindow instance method to its delegate instance.

Public Delegate Sub ShowValue

Public Class Name
   Private instanceName As String 

   Public Sub New(name As String)
      Me.instanceName = name
   End Sub 

   Public Sub DisplayToConsole()
      Console.WriteLine(Me.instanceName)
   End Sub    

   Public Sub DisplayToWindow()
      MsgBox(Me.instanceName)
   End Sub    
End Class 

Public Module testDelegate
   Public Sub Main()
      Dim testName As New Name("Koani")
      Dim showMethod As ShowValue = AddressOf testName.DisplayToWindow
      showMethod   
   End Sub 
End Module

The following example simplifies this code by instantiating the Action delegate instead of explicitly defining a new delegate and assigning a named method to it.

Public Class Name
   Private instanceName As String 

   Public Sub New(name As String)
      Me.instanceName = name
   End Sub 

   Public Sub DisplayToConsole()
      Console.WriteLine(Me.instanceName)
   End Sub    

   Public Sub DisplayToWindow()
      MsgBox(Me.instanceName)
   End Sub    
End Class 

Public Module testDelegate
   Public Sub Main()
      Dim testName As New Name("Koani")
      Dim showMethod As Action = AddressOf testName.DisplayToWindow
      showMethod   
   End Sub 
End Module

You can also use the Action 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;
using System.Windows.Forms;

public class Name
{
   private string instanceName;

   public Name(string name)
   {
      this.instanceName = name;
   }

   public void DisplayToConsole()
   {
      Console.WriteLine(this.instanceName);
   }

   public void DisplayToWindow()
   {
      MessageBox.Show(this.instanceName);
   }
}

public class Anonymous
{
   public static void Main()
   {
      Name testName = new Name("Koani");
      Action showMethod = delegate() { testName.DisplayToWindow();} ;
      showMethod();
   }
}

You can also assign a lambda expression to an Action delegate instance, as the following example illustrates. (For an introduction to lambda expressions, see Lambda Expressions (C# Programming Guide).)

Public Class Name
   Private instanceName As String 

   Public Sub New(name As String)
      Me.instanceName = name
   End Sub 

   Public Function DisplayToConsole() As Integer
      Console.WriteLine(Me.instanceName)
      Return 0
   End Function 

   Public Function DisplayToWindow() As Integer 
      Return MsgBox(Me.instanceName)
   End Function       
End Class 

Module LambdaExpression
   Public Sub Main()
      Dim name1 As New Name("Koani")
      Dim methodCall As Action = Sub() name1.DisplayToWindow()
      methodCall()
   End Sub 
End Module

.NET Framework

Supported in: 4.5.3, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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