Extending Built-In Web Controls - ASP.NET

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Overview¶

Although you can create a server control within its own project, sometimes you just want to extend a built-in ASP.NET web control for a single website. Here's how.

Walkthrough¶

Create Extender Class¶

Create yourself a new class in the App_Code folder of your website, naming the class whatever you like.
Have the class inherit from whatever control you like in the System.Web.UI.WebControls namespace.
Be sure to specify a namespace for your class — you'll need it for the web.config file.
Add whatever methods and properties you require.

Configure Your Website¶

In the Web.Config file, add the following entry. This allows you to bypass the adding of the <%@ Register %> tag at the top of each page where you want to use the server control.

<system.web>
  <pages>
    <controls>
      <add tagPrefix="tag" namespace="namespace" />
      ...
    </controls>
  </pages>
<system.web>

Implement your Control¶

You can reference the new control in your ASPX code as follows.

The tag is the same as the tag you specified in the web.config file
The className is simply the name of the class you just created above.

<tag:className runat="server" ... />