Thursday, June 11, 2009

UpdatePanel Control Overview


ASP.NET UpdatePanel controls enable you to build rich, client-centric Web applications. By using UpdatePanel controls, you can refresh selected parts of the page instead of refreshing the whole page with a postback. This is referred to as performing a partial-page update. A Web page that contains a ScriptManager control and one or more UpdatePanelcontrols can automatically participate in partial-page updates, without custom client script.

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The UpdatePanel control is a server control that helps you develop Web pages with complex client behavior that makes a Web page appear more interactive to the end user. Coordinating between server and client to update only specified parts of a Web page usually requires in-depth knowledge of ECMAScript (JavaScript). However, by using theUpdatePanel control, you can enable a Web page to participate in partial-page updates without writing any client script. If you want, you can add custom client script to enhance the client user experience. When you use an UpdatePanelcontrol, the page behavior is browser independent and can potentially reduce the amount of data that is transferred between client and server.


UpdatePanel controls work by specifying regions of a page that can be updated without refreshing the whole page. This process is coordinated by the ScriptManager server control and the client PageRequestManager class. When partial-page updates are enabled, controls can asynchronously post to the server. An asynchronous postback behaves like a regular postback in that the resulting server page executes the complete page and control life cycle. However, with an asynchronous postback, page updates are limited to regions of the page that are enclosed in UpdatePanel controls and that are marked to be updated. The server sends HTML markup for only the affected elements to the browser. In the browser, the client PageRequestManager class performs Document Object Model (DOM) manipulation to replace existing HTML with updated markup. The following illustration shows a page that is loaded for the first time, and a subsequent asynchronous postback that refreshes the content of an UpdatePanel control.