You can use the Action`2 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 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.

When you use the Action`2 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.

code reference: System.Action~2#1

The following example simplifies this code by instantiating the Action`2 delegate instead of explicitly defining a new delegate and assigning a named method to it.

code reference: System.Action~2#2

You can also use the Action`2 delegate with anonymous methods in C#, as the following example illustrates. (For an introduction to anonymous methods, see Anonymous Methods (C# Programming Guide).)

code reference: System.Action~2#3

You can also assign a lambda expression to an Action`2 delegate instance, as the following example illustrates. (For an introduction to lambda expressions, see Lambda Expressions (C# Programming Guide).)

code reference: System.Action~2#4

Namespace: System
Assembly: System.Core (in System.Core.dll)
Assembly Versions: 3.5.0.0