Extension Method in Asp.Net with C#

What is an Extension Method?

Extension methods enable us to add new methods to existing types.

Then what makes it so different?

• To do it we are not required to modify the existing type.
• No Inheritance is involved.
• They are static by nature (but called as if they are instance methods on the extended type).

How to create?

Step 1

Create a static class called PageExtensions as:

public static class ClsPageExtenions

{

}

Step 2

Create a static method IncludeJavaScript and IncludeStylesheet in that class as:
 

public static void IncludeJavascript(this Page objPage, string strJsPath)

{

    HtmlGenericControl objJs = new HtmlGenericControl();

    objJs.TagName = "script";

    objJs.Attributes.Add("type", "text/javascript");

    objJs.Attributes.Add("language", "javascript");

    objJs.Attributes.Add("src", objPage.ResolveClientUrl("~/Javascript/" +
    strJsPath));

    objPage.Header.Controls.Add(objJs);

}

public static void IncludeStylesheet(this Page objPage, string strCssPath)

{

    HtmlGenericControl objCss = new HtmlGenericControl();

    objCss.TagName = "link";

    objCss.Attributes.Add("type", "text/css");

    objCss.Attributes.Add("rel", "stylesheet");

    objCss.Attributes.Add("href", objPage.ResolveClientUrl("~/CSS/" + strCssPath));

    objPage.Header.Controls.Add(objCss);

}

Note: The first parameter must be preceded this modifier, telling the compiler that this is an extension method for the Page Class.

Step 3

Create the client code as:
 

protected void Page_Load(object sender, EventArgs e)

{

          this.IncludeJavascript("MyJs.js");

          this.IncludeStylesheet("MyCss.css");

}

That's it, for the client code there will not be any difference between normal methods and Extension methods.