Action<T1, T2, T3> Delegate

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.

Type Parameters

in T1

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

in T2

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

in T3

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

You can use the Action<T1, T2, T3> 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 three 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. It can also be a method that returns a value that is ignored.) Typically, such a method is used to perform an operation.

Note
To reference a method that has three parameters and returns a value, use the generic Func<T1, T2, T3, TResult> delegate instead.

When you use the Action<T1, T2, T3> delegate, you do not have to explicitly define a delegate that encapsulates a method with three parameters. For example, the following code explicitly declares a delegate named StringCopy and assigns a reference to the CopyStrings method to its delegate instance.

The following example simplifies this code by instantiating the Action<T1, T2, T3> delegate instead of explicitly defining a new delegate and assigning a named method to it.

You can also use the Action<T1, T2, T3> 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 TestAnon
{
   public static void Main()
   {
      string[] ordinals = {"First", "Second", "Third", "Fourth", "Fifth"};
      string[] copiedOrdinals = new string[ordinals.Length];           
      Action<string[], string[], int> copyOperation = delegate(string[] s1, 
                                                               string[] s2, 
                                                               int pos) 
                                      { CopyStrings(s1, s2, pos); };
      copyOperation(ordinals, copiedOrdinals, 3);
      foreach (string ordinal in copiedOrdinals)
         Console.WriteLine(String.IsNullOrEmpty(ordinal) ? "<None>" : ordinal);
   }

   private static void CopyStrings(string[] source, string[] target, int startPos)
   {
      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 <= source.Length - 1; ctr++)
         target[ctr] = String.Copy(source[ctr]);
   }
}

You can also assign a lambda expression to an Action<T1, T2, T3> delegate instance, as the following example illustrates. (For an introduction to lambda expressions, see Lambda Expressions (C# Programming Guide).)