"Use the IsInAsyncPostBack property of the ScriptManager .
It returns a boolean value that can be used to check for partial page postbacks.
Partial Page PostBack:
It is the mechanism through which a particular area of a web page is updated when
some postback occurs.The whole page is not updated when the postback
occurs. It results in performance improvement.
AJAX Technology provides us with a Control known as UpdatePanel which is used for partial page postbacks.
example: if we place a button and a Label inside UpdatePanel, and write code to display some text on the Label, the whole
page will not be posted and updated.
The indicator progressbar in the browser statusbar will not be visible in this case.