Delegate and event in C#

Delegate in C#:-

It is called a function pointer means we can point to the address of a function using a delegate to call the actual function.

If we do not want to call a particular function in the program then we can use the delegate concepts to call that function indirectly.

means we can say that delegate is an intermediate between function and object.

Syntax of Delegate:-

public delegate returntype  delegatename();

Type of Delegate:-

1) Single Cast  Delegate:-  We can call one delegate to one function

class DelegateExample
    {
        public void fun()
        {
            Console.WriteLine("Fun");
        }
        public delegate void mydelegate();
        static void Main()
        {
            DelegateExample del = new DelegateExample();
            mydelegate obj = new mydelegate(del.fun);
            obj();
            Console.ReadKey();
        }
    }
2) Multicast Delegate:-  We can \point one delegate to multiple functions address

public delegate void delegatename(param);
class DelegateExample
    {
        public void fun()
        {
            Console.WriteLine("Fun");
        }
        public void fun1()
        {
            Console.WriteLine("Fun1");
        }
        public void fun2()
        {
            Console.WriteLine("Fun2");
        }
        public delegate void mydelegate();
        static void Main()
        {
            DelegateExample del = new DelegateExample();
            mydelegate obj = new mydelegate(del.fun);
            obj += del.fun1;
            obj += del.fun2;
            obj();
            Console.ReadKey();
        }
    }

Another Example of Delegate in C#:-

class DelegateExample

    {

        public void fun1()

        {

            Console.WriteLine("Delegate Example");

        }

        public void fun2()

        {

            Console.WriteLine("Delegate Example2");

        }

       public delegate void mydelegate();

       static void Main()

       {

           DelegateExample obj = new DelegateExample();

           mydelegate del = new mydelegate(obj.fun1);

           del += obj.fun2;  //del = del + obj.fun2

           del -= obj.fun1;

           del();

           Console.ReadLine();

       }

    }

Multicast Delegate Example in C#:-

 class DelegateExample

    {

        public delegate void Mydelegate(int a,int b);

        public void fun(int a, int b)

        {

            Console.WriteLine(a+b);

        }

        public void fun1(int a, int b)

        {

            Console.WriteLine(a-b);

        }

        public void fun2(int a, int b)

        {

            Console.WriteLine(a*b);

        }

        public static void Main()

        {

            DelegateExample obj = new DelegateExample();

            Mydelegate del = new Mydelegate(obj.fun);

            del += obj.fun1;

            del += obj.fun2;

            del(10,2);

            del -= obj.fun2;

            del(100, 20);

          

            Console.ReadKey();

        }

    }

Event in c#:

it is a notification send by an object to singnal the ocuurence of an action, event contains two classes first is publisher and another one is subscriber. publisher publish the message and it will be received by subscriber class.

Delegate is the part of the event and it point to method.

Event is mainly used into GUI programming for example if we click on button then click is the event.

Now i am providing simple example of event.

public delegate void CUstomEventHandler(string message);

internal class Publisher

{

   

    public event CUstomEventHandler? RaiseEvent; // Declaring the event as nullable to fix CS8618.

    public void TriggerEvent()

    {

        Console.WriteLine("Event is being triggered...");

        if (RaiseEvent != null)

        {

            RaiseEvent.Invoke("hello");

        }

    }

}

internal class Program

{

    private static void Publisher_RaiseEvent(string message)

    {

        Console.WriteLine("Event Received with message: " + message);

    }

    static void Main(string[] args)

    {

        Publisher publisher = new Publisher();

        publisher.RaiseEvent += Publisher_RaiseEvent;//Subscribing to the event

        publisher.TriggerEvent();

}

}