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

Named methods
Anonymous methods
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);