Defines a control inside a UpdatePanel control as a postback control.
Use the PostBackTrigger control to enable controls inside an UpdatePanel to cause a postback instead of performing an asynchronous postback.
Use the RegisterPostBackControl(Control) method of the ScriptManager control to programmatically register a postback control. You can then call the Update() method of the UpdatePanel control when the trigger control performs a postback.
Programmatically adding PostBackTrigger controls is not supported.
If a control is set as both a PostBackTrigger and AsyncPostBackTrigger control, an exception is thrown.
The following example shows how to declaratively define a PostBackTrigger control for an UpdatePanel control. In the panel, a FileUpload control enables users to upload a file. Users must first check whether the file to upload exists. The Button control that calls the event handler to check the file name causes an asynchronous postback. However, the Button control that uploads the file is registered as a PostBackTrigger, because files cannot be uploaded asynchronously.
Assembly: System.Web.Extensions (Module: System.Web.Extensions)