All told, over 9kb of data is sent, when in fact only five bytes of data were needed to make this particular request. The response portion of the Update Panel's update request is shown in the Firebug console display on the left; it is a specially-formulated pipe-delimited string that is broken up by the client script and then reassembled on the page. NET AJAX sets the property of the HTML element on the client that represents your Update Panel.
It then checks to see whether an error was reported, and if so, processes the details of it, finally indicating to the runtime that the error was handled in custom script.
The Script Manager control provides extensive support for localization of script strings and user interface components; however, that topic is outside of the scope of this whitepaper.
Each Update Panel is isolated, so that each can work independently (you can have two Update Panels running at the same time, rendering different parts of the page, independent of the page's postback).
The Update Panel control primarily deals with control triggers - by default, any control contained within an Update Panel's that creates a postback is registered as a trigger for the Update Panel.
An Update Panel can be added to any user control or custom control; however, the page on which these controls are included must also include a Script Manager control with the property Enable Partial Rendering set to true.
One way in which you might account for this when using Web Custom Controls is to override the protected class.
To understand how the Update Panel works, so that you can best decide when its use is appropriate, you should examine the AJAX exchange.
The following example uses an existing site and, Mozilla Firefox with the Firebug extension (Firebug captures XMLHttp Request data).
By doing so, you can inject an Update Panel between the control's children and the outside world if you determine the page supports partial rendering; otherwise, you can simply layer the child controls into a container instance.
The Update Panel operates as something of a black-box, wrapping ASP.
This whitepaper is based on the Beta 2 release of the Visual Studio 2008 and the . NET AJAX Extensions into the Base Class Library (where it was previously an add-on component available for ASP. This whitepaper also assumes that you are using Visual Studio 2008 and not Visual Web Developer Express Edition; some project templates that are referenced may not be available to Visual Web Developer Express users. NET AJAX Extensions is the ability to do a partial or incremental page updates without doing a full postback to the server, with no code changes and minimal markup changes.