Delegate in C#

Delegate(s): A delegate is a reference type variable that holds the reference to a method.

1. Declare Delegate:Following is a syntax for declaring a delegate

delegate <return type> delegatename(parameter....)

e.g.

 delegate int Add(int x, int y);

If you feel problem to remember syntax of declaring delegate, just remember how we declare n abstract method and prefix delegate keyword instead of abstract keyword.

2. Create object of delegate

Add _a; 

3. Pass method which need to be called by delegate

 There are three methods by which we can invoke or call delegate

1. Named methods
2. Anonymous methods
3. Lambda Expression

1. Named Method-This is the traditional method which is available from detent 1.0.mechanism .In this we create a method and pass it to object of delegate we had created in Step 2

• 3.1.1 Create a method Add

  static int AddNum(int x, int y) 
  {
      return x + y;
  }
   

• 3.1.2 Use Delegate object and invoke add function
  
   _a = AddNum;         

2. C#2.0 introduces a new mechanism for calling delegate known as Anonymous methods

 In Anonymous method instead of creating a method and passing it to delegate object as we do in case of Named method. We passed a code of block to delegate. This will reduce the coding overhead in instantiating delegates by eliminating the need to create a separate method. 

Add _a = delegate(int x, int y)
{
    return x + y;
};

3. A lambda expression is an anonymous function that you can use to create delegates 

_a =( int x,int y) => x + y;

 4.0 Now you can invoke the delegate, irrespective by which mechanism we had pass delegate code to it.

 int returnValue=_a(10, 12);