Beginning ASP.NET 3.5: In C# and VB

10.5. Summary

Ajax is a broad and very interesting technology that can really add a lot of value to your site. It can be divided in two different areas: the server-side controls and the client-side JavaScript Framework.

To start with, the UpdatePanel control enables you to create flicker-free pages in no time. All you need to do is wrap some content in an UpdatePanel control, add a ScriptManager, and you're done. To avoid adding the ScriptManager to every single page that needs it, you can add it to the master page for the site so it becomes available throughout the site.

Although the UpdatePanel solves some problems related to ugly page refreshes, it also comes with its own issues. Because the page no longer really reloads, the user may be unaware of the fact the page is busy processing and may start clicking buttons again, causing problems at the server, like the same e-mail message being sent more than once. To overcome this problem, you should consider attaching an UpdateProgress control to every UpdatePanel you use. The contents of the UpdateProgress control are shown during an Ajax page refresh, so the user gets a visual cue something is going on. To stop the UpdateProgress from showing up during very short page refreshes, you set the DisplayAfter property, which postpones the display of the UpdateProgress for the specified amount of time.

Besides these very useful server-side controls, the ASP.NET AJAX Framework also comes with a rich client-side framework that enables ...