Action<T1, T2, T3> Delegate
Updated: October 2010
Encapsulates a method that takes three parameters and does not return a value.
Namespace: System
Assembly: mscorlib (in mscorlib.dll)
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 2678dc63-c7f9-4590-9ddc-0a4df684d42e.
- 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.
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.
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.
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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 two 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 rather than 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.
using System; public class Example { public static void Demo(System.Windows.Controls.TextBlock outputBlock) { 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) outputBlock.Text += String.Format("{0}\n", 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 a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.
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