C# delegates

In C#, a delegate is a pointer to a method. That means, a delegate holds the address of a method which can be called using that delegate.

Let's learn how we can define and execute a delegate.

Define a delegate

We define a delegate just like we define a normal method. That is, delegate also has a return type and parameter. For example,

public delegate int myDelegate(int x);

Here,

• delegate - a keyword
• int - return type of delegate
• myDelegate - delegate name
• int x - parameter that the delegate takes

Any method from any accessible class or struct that matches the delegate signature can be assigned to the delegate.

Note: A delegate is also called type-safe pointer.

Instantiate a delegate

Suppose, we have a method named calculateSum() whose signature is the same as myDelegate.

To create an instance of myDelegate, we pass a method name as a parameter. For example,

myDelegate d1 = new myDelegate(calculateSum);

Example: Calling a Method Using delegate

using System;
using System.Collections.Generic;
class Program
{
    // define a method that returns sum of two int numbers 
    static int calculateSum(int x, int y)
    {
        return x + y;
    }

    // define a delegate
    public delegate int myDelegate(int num1, int num2);

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

        // calling calculateSum() using delegate
        int result = d(5, 6);

        Console.WriteLine(result);
    }
}

Output

11

In the above example, we have created an instance of myDelegate d) and passed calculateSum() as a parameter.

Here, we have called the calculateSum() method by passing 5 and 6 as parameters values in d.

Use of C# delegates

We can use delegates to:

• promote reusability of code and implement flexibility
• notify which method to call when an event is triggered
• define callback methods

using System;
class Program
{
    // method that prints sum of two int numbers 
    public void sum(int x, int y)
    {
        Console.WriteLine("Sum is: " + (x + y));
    }

    // method that prints difference of two int numbers 
    public void difference(int x, int y)
    {
        Console.WriteLine("Difference is: " + (x - y));
    }

    // define a delegate of int type 
    public delegate void myDelegate(int num1, int num2);

    static void Main()
    {
        // instance of Program class
        Program obj = new Program();

        // create an instance of delegate and
        // pass sum method as a parameter 
        myDelegate d = new myDelegate(obj.sum);

        // multicast delegate 
        // calls difference() method 
        d += obj.difference;

        // pass values to two methods i.e sum() and difference()
        d(6, 5);
    }
}

Sum is: 11
Difference is: 1