Expand Minimize

Action<T1, T2> Delegate

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

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

public delegate void Action<in T1, in T2>(
	T1 arg1,
	T2 arg2
)

Type Parameters

in 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.

in T2

The type of the second 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.

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.

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.

using System;
using System.IO;

delegate void ConcatStrings(string string1, string string2);

public class TestDelegate
{
   public static void Main()
   {
      string message1 = "The first line of a message.";
      string message2 = "The second line of a message.";
      ConcatStrings concat;

      if (Environment.GetCommandLineArgs().Length > 1)
         concat = WriteToFile;
      else
         concat = WriteToConsole;

      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();
      }      
   }
}

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.

using System;
using System.IO;

public class TestAction2
{
   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 = WriteToFile;
      else
         concat = WriteToConsole;

      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 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).)

using System;
using System.IO;

public class TestLambdaExpression
{
   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 = (s1, s2) => WriteToFile(s1, s2);
      else
         concat = (s1, 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();
      }      
   }
}

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 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

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

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.

Was this page helpful?
(1500 characters remaining)
Thank you for your feedback
Show:
© 2014 Microsoft