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Callbacks (AJAX)

This sample demonstrates the use of the AJAX-based callbacks implemented by the ASPxTreeView control.

The ASPxTreeView control supports AJAX technology by implementing the ability to load the content of an ASPxTreeView from the server via a callback. This approach allows the ASPxTreeView to avoid the initial transfer of all its node data to the client, optimizing the page's load time.

In order to enable the use of callbacks, ASPxTreeView's EnableCallBacks property should be set to true and the AutoPostBack property should be set to false. In this instance, the contents of the collapsed nodes are not represented on the client. When a node is expanded for the first time, its content is retrieved from the server, and then cached on the client. The next time the node is expanded, its content is taken from the client and no callback to the server is performed.

Note that in this example, we purposely pause callback processing on the server side for a second, in order to make the Loading Panel visible during this time.

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The source code files for this demo are installed (by default) in the following directories:
\Users\Public\Documents\DevExpress Demos XX.X\Components\ASP.NET\CS\ASPxNavigationAndLayoutDemos
\Users\Public\Documents\DevExpress Demos XX.X\Components\ASP.NET\VB\ASPxNavigationAndLayoutDemos