Delegate in C#

Delegate:

C# delegates are similar to pointers to functions, in C or C++. A delegate is a reference type variable that holds the reference to a method. The reference can be changed at runtime.

Delegates are especially used for implementing events and the call-back methods. All delegates are implicitly derived from the System.Delegate class.

Basically delegates in c# are type safe objects which are used to hold reference of one or more methods in c#.net.

Delegates concept will match with pointer concept of c language. 

Suppose if you have multiple methods with same signature (return type & number of parameters)

and want to call all the methods with single object then we can go for delegates.

Single Cast Delegates:

Single cast delegate means which hold address of single method like as explained in above example.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace Practice

{

    class Program

    {

        static void Main(string[] args)

        {

            Delegate d = new Delegate();

            d.call();

        }

    }

}

public delegate int delegateMethod(int a,int b);

    class Delegate

    {

        public int Add(int x,int y)

        {

            return x + y;

        }

        public int Sub(int x, int y)

        {

            return x - y;

        }

        public void call()

        {

            Delegate dadd = new Delegate();

            delegateMethod d1 = dadd.Add;

            int i = d1(20, 10);

            Console.WriteLine(i);

            Delegate dsub = new Delegate();

            delegateMethod d2 = dsub.Sub;

            int j = d2(30, 10);

            Console.WriteLine( j);

        }

    }

Output

30

20

Multicast Delegates:

Multi cast delegate is used to hold address of multiple methods in single delegate.

To hold multiple addresses with delegate we will use overloaded += operator and 

if you want remove addresses from delegate we need to use overloaded operator -=

Multicast delegates will work only for the methods which have return type only void.

If we want to create a multicast delegate with return type we will get the return type of last method in the invocation list

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace Practice

{

    class Program

    {

        static void Main(string[] args)

        {

       multicastdelegate d = new multicastdelegate();

            d.call();

        }

    }

}

public delegate void Multidelegate(int x,int y);

    class multicastdelegate

    {

        public void Add(int x, int y)

        {

            Console.WriteLine("Add " +( x+y));

        }

        public void Sub(int x, int y)

        {

            Console.WriteLine("Sub " +( x-y));

        }

        public void Mul(int x, int y)

        {

            Console.WriteLine("mul " + (x * y));

        }

        public void call()

        {

            multicastdelegate mc = new multicastdelegate();

            Multidelegate md = mc.Add;

            md += mc.Sub;

            md += mc.Mul;

            md(20, 10);

        }

    }

Output

Add 30

Sub 10

Mul 200