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Extension Method In C#

In this article, we will discuss extension methods in C#.

Purpose

An extension method is used to add your method to the existing class of .net framework.

Scenario

Consider a scenario where you are working on a mathematical project and a scenario comes in which you need to check if the number is even or not.

You can use the following 2 approaches: -

Create a custom class and add a method IsEvenNumber in it
Create an extension method

Let us discuss both approaches.

Create A Custom Class

The first step is to create a custom class.

public class UsefulFunctions { 
    public bool IsEvenNumber(int num) {… 
    } 
}

In the above code, a custom class UsefulFunctions is created, and inside the class a method IsEvenNumber is defined. The purpose of this method is to check whether the number is even or not. This function accepts a parameter of type integer and returns Boolean.

To use this method programmer will create an instance of the class and then call the method. Now an obvious solution comes to your mind is – Why should I create an instance of the class I will create a static method and use it like class_name.method_name.

Yes, you can do that, but consider a scenario where 15-20 programmers are working on a project. Out of them, one programmer creates a function say CheckDBNull to check the null value and other programmers also create the function with some other name (or maybe be same name) that does the same functionality. The result is code redundancy. Or if everything goes well and the scenario mentioned above does not happen then also the programmer has to remember a new class name.

It is always good if we can include the functionality you require in the existing .net framework classes. To accomplish that purpose Microsoft introduced extension methods in .net.

Create Extension Method

To implement the extension method in C#: -

Create a static class
Inside the class create a static method
Pass an argument of any data type of which you want to write the extension method prefixed by this keyword

public static class ExtensionMethodsClass { 
    public static bool IsEvenNumber(this int num) { 
        bool status = false; 
        if (num % 2 == 0) { 
            status = true; 
        } 
        return status; 
    } 
}

Now to use that method

int x = 3; 
MessageBox.Show(x.IsEvenNumber().ToString());

This message box will pop up a False message because 3 is not an even number.

Posted By -	Karan Gupta

Posted On -	Wednesday, February 23, 2011

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