Action(T1, T2) Delegate
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Action<'T1, 'T2> Delegate

 

Encapsulates a method that has two parameters and does not return a value.

Namespace:   System
Assembly:  mscorlib (in mscorlib.dll)

type Action<'T1, 'T2> = 
    delegate of 
        arg1:'T1 *
        arg2:'T2 -> unit

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.

Type Parameters

inT1

The type of the first parameter of the method that this delegate encapsulates.

inT2

The type of the second parameter of the method that this delegate encapsulates.

You can use the Action<'T1, 'T2> 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 two parameters that are both 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 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.

System_CAPS_noteNote

To reference a method that has two parameters and returns a value, use the generic Func<'T1, 'T2, 'TResult> delegate instead.

When you use the Action<'T1, 'T2> delegate, you do not have to explicitly define a delegate that encapsulates a method with two parameters. For example, the following code explicitly declares a delegate named ConcatStrings. It then assigns a reference to either of two methods to its delegate instance. One method writes two strings to the console; the second writes two strings to a file.

No code example is currently available or this language may not be supported.

The following example simplifies this code by instantiating the Action<'T1, 'T2> delegate instead of explicitly defining a new delegate and assigning a named method to it.

No code example is currently available or this language may not be supported.

You can also use the Action<'T1, 'T2> 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.IO;

public class TestAnonymousMethod
{
   public static void Main()
   {
      string message1 = "The first line of a message.";
      string message2 = "The second line of a message.";
      Action<string, string> concat;

      if (Environment.GetCommandLineArgs().Length > 1)
         concat = delegate(string s1, string s2) { WriteToFile(s1, s2); };
      else
         concat = delegate(string s1, string s2) { WriteToConsole(s1, s2);} ;

      concat(message1, message2);
   }

   private static void WriteToConsole(string string1, string string2)
   {
      Console.WriteLine("{0}\n{1}", string1, string2);            
   }

   private static void WriteToFile(string string1, string string2)
   {
      StreamWriter writer = null;  
      try
      {
         writer = new StreamWriter(Environment.GetCommandLineArgs()[1], false);
         writer.WriteLine("{0}\n{1}", string1, string2);
      }
      catch
      {
         Console.WriteLine("File write operation failed...");
      }
      finally
      {
         if (writer != null) writer.Close();
      }      
   }
}

You can also assign a lambda expression to an Action<'T1, 'T2> delegate instance, as the following example illustrates. (For an introduction to lambda expressions, see Lambda Expressions (C# Programming Guide).)

No code example is currently available or this language may not be supported.

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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