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02.22.07
ASP.NET - A Simpler AJAX Implementation
 By Mads Kristensen
A week ago I wrote about the native client callback feature of ASP.NET 2.0 and why it isn't always the smart choice.
That post got me some good feedback that inspired me to build a custom callback implementation so you wouldn't have to use the native one. I could just use other AJAX libraries such as ASP.NET AJAX or Ajax.NET, but that's not fun.
When I started thinking about this little project I imagined it to be complex, but actually it turned out to be extremely simple with very little code. It is less than 100 lines of code including the JavaScript and code comments. Remember, that this is not an all-in-one AJAX framework, but a simple and fast way to do client callbacks.
Good things
•
Uses GET instead of POST for performance reasons
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Doesn't send the ViewState to eliminate the overhead
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Simple implementation
Limitations
Because it doesn't send the ViewState you are not able to check the state of the controls on the page. You can use the Session and Cache and any other store, just not the ViewState. You cannot implement it on custom server controls, because it only works on pages.
Implementation
The solution consists of two things: a base class for the page and a small JavaScript file.
Step 1 - change inheritage
In the page you want to do client callbacks, just inherit from CallbackPage instead of System.Web.UI.Page and override the IncommingCallback(string argument, string context) method. Here is an example of such a page's code-behind file.
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Step 2 - Insert JavaScript
Next, add the JavaScript file to the header of the HTML document or copy its content into your own script file.
The JavaScript file contains one method that creates the callbacks and it is called CreateCallback. I'll show you how to use it below. That's the entire implementation.
Example of use
Let's imaging that we want a text box where the visitors write their name. When they click a button, it verifies the entered name server-side and sends the result to a JavaScript function.
Continue reading this article.
About the Author:
Mads Kristensen currently works as a Senior Developer at Traceworks located
in Copenhagen, Denmark. Mads graduated from Copenhagen Technical Academy with a multimedia degree in
2003, but has been a professional developer since 2000. His main focus is on ASP.NET but is responsible for Winforms, Windows- and
web services in his daily work as well. A true .NET developer with great passion for the simple solution.
http://www.madskristensen.dk/
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