In this chapter, you will first be introduced to how ASP.NET server controls work.
After that, you??™ll be given an overview of the ASP.NET AJAX architecture, taken on a tour
of the AJAX Library, and shown how the AJAX Extensions integrate with ASP.NET 2.0.
Introducing ASP.NET 2.0 Server Controls
Understanding the ASP.NET 2.0 AJAX Extensions and how they are architected first
requires an understanding of what ASP.NET 2.0 server controls are and how they work.
Server controls are a fundamental part of the ASP.NET framework. At their core, server
controls are .NET Framework classes that provide visual elements on a web form as well
as the functionality that these elements offer. An example of this is a drop-down list box
control. ASP.NET provides a server-side ListBox control that renders a list box as HTML
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C H A P T E R 2
elements on the web page. When the web page is returned to the browser, the browser
displays the list box to the user. When the user selects an item in the list box, you can run
client-side JavaScript to handle the event locally. Alternatively (or additionally), you can
arrange for a postback to the server to happen; server-side code can handle the user's
selection and perform some related server-side operation (such as populating another
part of the web page with data relating to the user??™s selection).
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