Click here to Skip to main content
11,705,610 members (52,037 online)
Click here to Skip to main content

Tagged as

Extension Methods in C#

, 21 Jul 2011 CPOL 4.3K 2
Rate this:
Please Sign up or sign in to vote.
                                             As name implies extension methods allow existing classes to be extended without using inheritance or changing class’s source code.Some important points when using extension methods:•    You cannot use extension methods to override existing methods•    An

As name implies extension methods allow existing classes to be extended without using inheritance or changing class’s source code.

Some important points when using extension methods:

  • You cannot use extension methods to override existing methods
  • An extension method with the same name and signature as an instance method must not be called
  • The concept must not be applied to fields, properties or events
  • Do not overuse

As an example, we’ll create an extension method to existing ‘String’ class. We’ll implement the functionality of converting a string to a proper case. (Any given string will be converted to lower case, having the first letter of each word in upper case. E.g.: ‘this is sample text’ will be converted to ‘This Is Sample Text’)

Add a class and add the following code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ExtensionMethods {
public static class SampleExtensionMethods {
public static string ToProper(this string zSource) {
StringBuilder sb = new StringBuilder();

string zTemp = zSource.ToLower();
List<string> data = zTemp.Split(new char[] { ' ' }).ToList<string>();
if (data.Count > 0) {
foreach (string element in data) {
if (element.Trim().Length > 0) {
sb.Append(element.Trim().Substring(0, 1).ToUpper() + element.Trim().Substring(1, 
    element.Trim().Length - 1) + " ");

return sb.ToString().Trim();

please note that the class that the class should be static and the method should be public (Unless you are writing it within the same calss which you intend to use it). And also in input the parameter I have mentioned 'this'. This will tell the compiler to add the following method to the 'String' class.

Before using include the namspace. (I have used 'ExtensionMethods' as the namespace)

using ExtensionMethods;

And you can use the method we created using this syntax :



using System;
using System.Text;
using ExtensionMethods;

namespace SampleConsoleApplicationA {
class SampleExtMethod {
static void Main(string[] args) {
string zSample = "this is sample text";
Console.WriteLine("Input : " + zSample);
Console.WriteLine("Output : " + zSample.ToProper());


And if you run the application you can get the below output (I have used a console application to illustrate this)

Extension Method


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


About the Author

Manjuke Fernando
Technical Lead Air Liquide Industrial Services (Singapore)
Singapore Singapore
I have been in software industry for more than 8 years. I have developed different type of software using different languages. Many of them are database related (both web & window based), SQL being as the back end most of the time. Up-to-date I have knowledge in languages such as C#, VB.Net, T-SQL, JAVA, VB6 & C++, making C# the most proficient of all. Also I have worked using different technologies like ASP.Net, SharePoint, Crystal Reports (But I really hate designing reports) & MS SQL Server and have involved in designing & developing software for major companies like FedEx, Softlogic Holdings, IronOne Technologies & Brandix. Currently I am working as a Tech Lead in Singapore.

You may also be interested in...

Comments and Discussions

-- There are no messages in this forum --
| Advertise | Privacy | Terms of Use | Mobile
Web02 | 2.8.150819.1 | Last Updated 21 Jul 2011
Article Copyright 2011 by Manjuke Fernando
Everything else Copyright © CodeProject, 1999-2015
Layout: fixed | fluid