Posted by: R Manimaran | December 6, 2010

Extensions Method in C# 3.0

Extensions Method in C# 3.0

Extension methods enable you to “add” methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type.

Some C# Examples:

public static void UsingExtensionsMethod()
     string sampleText = "This is the Sample Text for Extensions Method";
     int count = sampleText.CountWords();
     string mailAddress = "";
     bool isValid = mailAddress.IsValidEmailAddress();
public static int CountWords(this string input)
    return input.Split(' ').Count();


If you check, you can see a small arrow in the Method which indicates it is an Extension Method.

public static bool IsValidEmailAddress(this string input)


Regex regex = new Regex(@"^[w-.]+@([w-]+.)+[w-]{2,4}$");

return regex.IsMatch(input);


If you look the extension method you have a common thing (this string input).The this keyword in front of the parameter string input makes this an extension method.

This Extension method needs to place in a Class which is also static.

In the next article we will create some SharePoint Extensions methods.


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