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Posted 10 Jan 2014

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Extension Method In C#

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10 Jan 2014CPOL2 min read
A brief discussion about extension methods in C#


Extension methods are a new feature in C# 3.0. An extension method enables us to add methods to existing types without creating a new derived type, recompiling, or modify the original types. We can say that it extends the functionality of an existing type in .NET. 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.

Feature and Property of Extension Methods 

The following list contains basic features and properties of extension methods:

  1. It is a static method.
  2. It must be located in a static class.
  3. 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.
  4. It also shown by VS intellisense. When we press the dot (.) after a type instance, then it comes in VS intellisense.
  5. 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.
  6. You can give any name for the class that has an extension method but the class should be static.
  7. If you want to add new methods to a type and you don't have the source code for it, then the solution is to use and implement extension methods of that type.
  8. If you create extension methods that have the same signature methods as the type you are extending, then the extension methods will never be called.

Using the Code

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.

Extension Method

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

Now we create a static class and two static methods, one for the total word count in a string and another for the total number of characters in a string without a space.

using System;
namespace ExtensionMethodsExample
   public static class Extension
       public static int WordCount(this string str)
           string[] userString = str.Split(new char[] { ' ', '.', '?' },
           int wordCount = userString.Length;
           return wordCount;
       public static int TotalCharWithoutSpace(this string str)
           int totalCharWithoutSpace = 0;
           string[] userString = str.Split(' ');
           foreach (string stringValue in userString)
               totalCharWithoutSpace += stringValue.Length;
           return totalCharWithoutSpace;

Now we create an executable program that has a string as an input and uses an extension method to count the total words in that string and the total number of characters in that string then show the result in a console screen.

using System;
namespace ExtensionMethodsExample
    class Program
        static void Main(string[] args)
            string userSentance = string.Empty;
            int totalWords = 0;
            int totalCharWithoutSpace = 0;
            Console.WriteLine("Enter the your sentance");
            userSentance = Console.ReadLine();
            //calling Extension Method WordCount
            totalWords = userSentance.WordCount();
            Console.WriteLine("Total number of words is :"+ totalWords);
            //calling Extension Method to count character
            totalCharWithoutSpace = userSentance.TotalCharWithoutSpace();
            Console.WriteLine("Total number of character is :"+totalCharWithoutSpace);

Extension Method


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Sandeep Singh Shekhawat
Software Developer
India India
He is awarded for Microsoft TechNet Guru, CodeProject MVP and C# Corner MVP.

Comments and Discussions

GeneralMy vote of 5 Pin
Mahsa Hassankashi14-Nov-17 6:24
MemberMahsa Hassankashi14-Nov-17 6:24 
GeneralMy vote of 5 Pin
3drinker24-Oct-16 23:55
Member3drinker24-Oct-16 23:55 
GeneralMy vote of 4 Pin
Umesh AP19-Jul-16 1:08
MemberUmesh AP19-Jul-16 1:08 
GeneralMy vote of 4 Pin
Member 113003727-May-15 0:46
MemberMember 113003727-May-15 0:46 
QuestionNice article. (Pretty much same from MSDN) Pin
SharmaMayank10-Feb-15 19:13
MemberSharmaMayank10-Feb-15 19:13 
Questionawasome Tips Pin
Yogesh Kumar Tyagi1-Dec-14 19:20
professionalYogesh Kumar Tyagi1-Dec-14 19:20 
GeneralPretty nice Pin
柏瑛 胡20-Nov-14 17:30
Member柏瑛 胡20-Nov-14 17:30 
GeneralRe: Pretty nice Pin
Sandeep Singh Shekhawat20-Nov-14 18:25
professionalSandeep Singh Shekhawat20-Nov-14 18:25 
GeneralVery Good article Pin
Deepan Maheswaran12-Nov-14 23:55
professionalDeepan Maheswaran12-Nov-14 23:55 
AnswerExtension method tutorial Pin
negatestac5-Nov-14 2:40
Membernegatestac5-Nov-14 2:40 
QuestionGood tip Pin
CJV_Xtream13-Jan-14 8:31
MemberCJV_Xtream13-Jan-14 8:31 
AnswerRe: Good tip Pin
Sandeep Singh Shekhawat13-Jan-14 18:47
professionalSandeep Singh Shekhawat13-Jan-14 18:47 
GeneralMy vote of 1 Pin
r.wcs13-Jan-14 6:07
Memberr.wcs13-Jan-14 6:07 
GeneralRe: My vote of 1 Pin
Sandeep Singh Shekhawat13-Jan-14 6:12
professionalSandeep Singh Shekhawat13-Jan-14 6:12 
QuestionThanks Pin
rtz8712-Jan-14 8:01
Memberrtz8712-Jan-14 8:01 
AnswerRe: Thanks Pin
Sandeep Singh Shekhawat12-Jan-14 18:14
professionalSandeep Singh Shekhawat12-Jan-14 18:14 
Question[My vote of 1] Nonsense Pin
FatCatProgrammer11-Jan-14 10:33
MemberFatCatProgrammer11-Jan-14 10:33 
AnswerRe: [My vote of 1] Nonsense Pin
Sandeep Singh Shekhawat12-Jan-14 21:49
professionalSandeep Singh Shekhawat12-Jan-14 21:49 
GeneralMy vote of 5 Pin
M Rayhan10-Jan-14 20:51
MemberM Rayhan10-Jan-14 20:51 
GeneralRe: My vote of 5 Pin
Sandeep Singh Shekhawat10-Jan-14 21:03
professionalSandeep Singh Shekhawat10-Jan-14 21:03 

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