Extension Method in C#

Tutorialsrack 28/04/2019 C#

In this article, we will learn about Extension Method in C# and how to create Extension Method in C#.

What is the Extension Method in C#?

Extension methods are a new feature in C# 3.0. An Extension method allows you to add your own methods to an existing type without creating a new derived type, recompiling, or otherwise modifying the original type. An extension method is a static method to the existing static class. We call an extension method in the same general way; there is no difference in calling.

They themselves should be static and should contain at least one parameter, the first preceded by the this keyword.

When working with extension methods, Remember these points and keep in mind:

• An Extension method must be static 
• It must be inside in a static class and you can give any name for the class that has an extension method.
• It uses the this keyword as the first parameter with a type in  .Net and this method will be called by a given type instance on the client side.
• Extension methods cannot be used to override existing methods.
• An extension method with the same name and signature as an instance method will not be called.
• An extension method should be in the same namespace as it is used or you need to import the namespace of the class by a using statement.

Benefits of Extension Methods:

1. Extension methods appear under the IntelliSense.
2. It makes the code more readable.
3. Extend the functionality of third party libraries where you don’t have access to the code. (This may also break your code if the third party vendor changes the implementation of the library).

How to create Extension Method

We create an extension method for a string type, so string will be specified as a parameter for this extension method and that method will be called by a string instance using the dot operator.

    public static class stringExtentionMethod
    {
        public static string CapitaliseWord(this string value)
        {
            // Uppercase the first letter in the string.
            if (value.Length > 0)
            {
                char[] array = value.ToCharArray();
                array[0] = char.ToUpper(array[0]);
                return new string(array);
            }
            return value;
        }

    }

In the above example, we create method CapitaliseWord(), we are passing a string type with this so it will be called by the string type variable, in other words a string instance.

In the above example, we create a method for converting the first letter of the given string into uppercase and the rest of character in a given string is remains the same.

Here is the complete program for creating and using the extension method.

using System;

namespace ExtensionMethod
{
    public static class stringExtentionMethod
    {
        public static string CapitaliseWord(this string value)
        {
            // Uppercase the first letter in the string.
            if (value.Length > 0)
            {
                char[] array = value.ToCharArray();
                array[0] = char.ToUpper(array[0]);
                return new string(array);
            }
            return value;
        }

    }
    class Program
    {
        static void Main(string[] args)
        {
            string str = "tutorials rack";
            //Using this Extention Method for convert the first letter of the string into uppercase.
            string Capitalise_Str = str.CapitaliseWord();
            Console.WriteLine("Result: {0}", Capitalise_Str);
            Console.ReadLine();

        }
    }
}

Conclusion

You can add extension methods to any type, even a value type. The original representation of the type does not change. Extension methods affect syntax, not execution.

I hope this article will help you to understand Extension Methods in C#.

Share your valuable feedback, please post your comment at the bottom of this article. Thank you!

Related Posts