What is Delegate?

 Delegate is a simple class that is used to point to methods with a specific signature, becoming essentially a type-safe function pointer. A delegate's purpose is to facilitate a call back to another method  (or methods), after one has been completed, in a structured way
Delegate is a type which  holds the method(s) reference in an object. It is also referred to as a type safe function pointer.

Advantages

• Encapsulating the method's call from caller
• Effective use of delegate improves the performance of application
• Used to call a method asynchronously

Declaration
Creating a delegate is easy to do. Identify the class as a delegate with the "delegate" keyword. Then specify the signature of the type.

public delegate type_of_delegate delegate_name()
Example.
public delegate double Integrand(double x);

public delegate double Delegate_Prod(int a,int b);
class ClassDel
{
    static double fn_Prodvalues(int val1,int val2)
    {
        return val1*val2;
} static void Main(string[] args) {   
        Delegate_Prod delObj = new Delegate_Prod(fn_Prodvalues);
        Console.Write("Please Enter Values");
        int v1 = Int32.Parse(Console.ReadLine());
        int v2 = Int32.Parse(Console.ReadLine());
        //use a delegate for processing        double res = delObj(v1,v2);
        Console.WriteLine ("Result :"+res);
        Console.ReadLine();
    }
}

.

What is Multicast Delegate?

It is a delegate which holds the reference of more than one method.

Multicast delegates must contain only methods that return void, else there is a run-time exception.

 

delegate void Delegate_Multicast(int x, int y);

Class Class2

{

    static void Method1(int x, int y)

    {

        Console.WriteLine("You r in Method 1");

    }

 

    static void Method2(int x, int y)

    {

        Console.WriteLine("You r in Method 2");

    }

 

    public static void <place w:st="on" />Main</place />()

    {

        Delegate_Multicast func = new Delegate_Multicast(Method1);

        func += new Delegate_Multicast(Method2);

        func(1,2);             // Method1 and Method2 are called

        func -= new Delegate_Multicast(Method1);

        func(2,3);             // Only Method2 is called

    }

}

 

 

Where use delegate?

 

• Event handlers (for GUI and more like Menu)
• Starting threads(like progress bar)
• Callbacks (e.g. for async APIs)
• LINQ and similar (List.Find etc)
• Anywhere else where I want to effectively apply "template" code with some specialized logic inside (where the delegate provides the specialization)
• Event Handling
• Multi Casting
• Filtering