C# Delegate

A delegate in C# is like a pointer to a method that allow you to pass methods as parameters, store methods for later execution. When you use a delegate, you can call a method indirectly, or even change the method it calls during runtime.

Syntax:

public delegate returnType DelegateName(parameterType parameterList);

Example of Delegate

There are many steps to define Delegate

Step 1: Declare a Delegate

We’ll declare a delegate called MyDelegate that will point to any method that takes a string as input and returns string.

 public delegate string MyDelegate(string message);

This delegate can now hold references to methods that match this signature (methods that take a string and return string).

Explanation:

We declare a delegate type MyDelegate that represents any method that takes a string parameter and returns string.

Step 2: Create a Method that Matches the Delegate’s Signature

We’ll create a method that matches the delegate’s signature.

public static string printMessage(string message)
{
        return message;
}

Explanation:

We define a method printMessage that matches the signature of the delegate.

Step 3: Instantiate the Delegate and Call the Method

Now we create an instance of the delegate and point it to the PrintMessage method.

public static void Main()
{
    // create an instance of delegate by passing method name 
        MyDelegate myDelegate  = new MyDelegate(printMessage);

        // calling printMessage() using delegate
        string result = myDelegate("Hello World!");

        Console.WriteLine(result);
}

Explanation:

In the Main method, we create an instance of the delegate, pointing it to myDelegate. We then invoke the delegate as if it were a method.

Complete Example:

using System;
using System.Collections.Generic;
class MyProgram
{
    
    
    public static string printMessage(string message)
    {
        return message;
    }

    // define a delegate
    public delegate string MyDelegate(string message);

    static void Main()
    {
        // create an instance of delegate by passing method name 
        MyDelegate myDelegate  = new MyDelegate(printMessage);

        // calling printMessage() using delegate
        string result = myDelegate("Hello World!");

        Console.WriteLine(result);
    }
}

Output:

Why Use Delegates?

1. Decoupling: Delegates allow you to separate the definition of the method from the place where it’s executed. This makes the code easier to maintain and extend.

2. Event Handling: Delegates are often used in event-driven programming (e.g., in UI applications).

3. Callback Methods: Delegates can be used to implement callback patterns, where you pass a method to another method to be invoked later.