Gets the unique ID of the control that caused the asynchronous postback.
Assembly: System.Web.Extensions (in System.Web.Extensions.dll)
The property contains the value of the control ID that caused the asynchronous postback, which can be one of the following:
A postback from a control that is a trigger for an UpdatePanel control.
Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.