C# .NET Delegates : How to use

The common blueprint for using delegates includes steps to define, create, and invoke a delegate.

1.       Define a classification of a delegate using the delegate keyword:

public delegate int DelegateClass(string info);

2.       Create an instance of a delegate using the new keyword. In the constructor, initialize the delegate with a function pointer. You can also create and initialize a delegate implicitly without the new keyword:

DelegateClass obj = new DelegateClass(MethodA); DelegateClass obj2 = MethodA; // implicit

3.       Invoke the delegate with the call operator “()”. The call operator is convenient, but makes it harder to discern a delegate invocation from a regular function call. Alternatively, invoke the delegate with the Invoke method, which clearly distinguishes invoking a delegate from a normal function call:

obj(“1″); obj.Invoke(“2″); // Alternative.

4.       As with any object, when the delegate is no longer needed, set the delegate to null:

obj=null;

The complete list of the example application follows:

using System;   namespace Examples.Delegates {     public delegate int DelegateClass(string info);       public class Steps     {         public static void Main()         {             DelegateClass obj = new DelegateClass(MethodA);             DelegateClass obj2 = MethodA; // implicit             int i = obj(“1″);             Console.WriteLine(i.ToString());             i = obj.Invoke(“2″); // Alternative             Console.WriteLine(i.ToString());             obj = null;             obj2 = null;               Console.ReadKey();         }           public static int MethodA(string info)         {             Console.WriteLine(“Steps.MethodA”);             return int.Parse(info);         }     } }