Delegates in C#

Introduction

A delegate is an object that can refer to a method. Therefore when you create a delegate, you are creating an object that can hold a reference to a method. The method can be called using this reference. In other words, a delegate can invoke the method and is considered to be a powerful feature.

Advantage

The same delegate can be used to call various methods during runtime of a program by simply changing the method. Therefore, thay is an advantage of a delegate.

Declaration

• A delegate type is declared by the keyword delegate.
• Delegate return-type name (parameter list);
• Where return-type defines the type of value returned by the methods.

Example

using System;
namespace ConsoleApplication3
{
    delegate string delegate_method(string str);
    class delegate_test
    {
        static string Reverse(string s)
        {
            string temp = "";
            int i, j;
            Console.WriteLine("Reversing String...");
            for (j = 0, i = s.Length - 1; i >= 0; i--, j++)
                temp += s[i];
            return temp;
        }
        static void Main(string[] args)
        {
            delegate_method del = new delegate_method(Reverse);
            string str;
            del = new delegate_method(Reverse);
            str = del("neeraj kumar");
            Console.WriteLine("Result is: "+str);
            Console.Read();
        }
    }
}

Output 

Reversing String…
Result is: ramuk jareen

The del object is assigned Reverse() then del is called. Then Reverse() is being called.

Delegate method group conversion

A delegate method group conversion defines the simple way of using a delegate. It simplifies the syntax that assigns a method to a delegate. It is called method group conversion.

static void Main(string[] args)
{
    delegate_method del = Reverse;//use method group conversion
    string str;
    del = new delegate_method(Reverse);
    str = del("neeraj kumar");
    Console.WriteLine("Result is: "+str);
    Console.Read();
}

Multicasting delegates

Delegates also support an exciting feature called multicasting. Multicasting is the ability to create a chain of methods that will be automatically called when a delegate is invoked and is easy to create. We use the + or the += operator to add methods to the chain and to remove the methods we use – or -=.

Example

using System;
namespace ConsoleApplication3
{
    delegate void delegate_method(ref string str);
    class delegate_test
    {
        static void Reverse(ref string s)
        {
            string temp = "";
            int i, j;
            Console.WriteLine("Reversing String...");
            for (j = 0, i = s.Length - 1; i >= 0; i--, j++)
                temp += s[i];
            s = temp;
        }
        static void Uppercase(ref string s)
        {
            Console.WriteLine("Converting into uppercase...");
            s = s.ToUpper();

        }
        static void Main(string[] args)
        {
            delegate_method del;
            delegate_method upper = Uppercase;
            delegate_method reverse = Reverse;
            string str="neeraj kumar";
            // setup multicasting
            del = upper;
            del += reverse;
            //call multicasting
            del(ref str);
            Console.WriteLine("Result is: "+str);
            Console.Read();
        }
    }
}

Output

Converting into uppercase…
Reversing String…
Result is: RAMUK JAREEN

I hope this article will help you understand delegates.