How to declare and instantiate delegates in C#?

C# A delegate is similar to a function pointer in C or C#. A delegate is a reference type variable that holds a reference to a method. References can be changed at runtime.

Syntax for declaring delegates -

delegate <return type> <delegate-name> <parameter list>

Now let’s see how to instantiate a delegate in C#.

After declaring a delegate type, you must use the new keyword to create a delegate object and associate it with a specific method. When you create a delegate, the parameters passed to the new expression are written like a method call, but without the method's parameters.

public delegate void printString(string s);
...
printString ps1 = new printString(WriteToScreen);
printString ps2 = new printString(WriteToFile);

The following is an example of declaring and instantiating a delegate in C# -

Example

Live Demonstration

using System;

delegate int NumberChanger(int n);
namespace DelegateAppl {

   class TestDelegate {
      static int num = 10;

      public static int AddNum(int p) {
         num += p;
         return num;
      }

      public static int MultNum(int q) {
         num *= q;
         return num;
      }

      public static int getNum() {
         return num;
      }

      static void Main(string[] args) {
         //create delegate instances
         NumberChanger nc1 = new NumberChanger(AddNum);
         NumberChanger nc2 = new NumberChanger(MultNum);

         //calling the methods using the delegate objects
         nc1(25);
         Console.WriteLine("Value of Num: {0}", getNum());
         nc2(5);
         Console.WriteLine("Value of Num: {0}", getNum());
         Console.ReadKey();
      }
   }
}

Output

Value of Num: 35
Value of Num: 175

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