How to: Determine How ASP.NET Web Forms Were Invoked
It is often useful to know how an ASP.NET Web page was invoked: whether by an original request (an HTTP GET), a postback (an HTTP POST), a cross-page post from another page (an HTTP POST), or a transfer from another page using the Transfer method or using a callback from the browser. The Page class exposes a set of properties that you can use to determine how a page was invoked.
To determine how an ASP.NET Web page was invoked
Examine the values of the following Page class properties, and then refer the table to determine how the page was invoked:
The following table lists ways in which a page can be invoked and the corresponding Page property values.