Used by the beginRequest event of the Sys.WebForms.PageRequestManager class to pass argument information to event handlers. The beginRequest event is raised just before the postback request is made.
This class contains private members that support the client-script infrastructure and are not intended to be used directly from your code. Names of private members begin with an underscore ( _ ).
Event handlers can use the request property to access the request object and the postBackElement property to determine the element that caused the postback.
The following example shows how to use the BeginRequestEventArgs class. Two buttons perform asynchronous postbacks. In the beginRequest event handler the postBackElement property is used to access the name of the element that caused the postback.