Gets a value indicating whether the page is being loaded in response to a client postback or if it is being loaded and accessed for the first time.

Property Value

true if the page is being loaded in response to a client postback; otherwise false.

void Page_Load() {
if (!IsPostBack) {
// Validate initially to force asterisks
// to appear before the first roundtrip.
Validate();
}
}

IPostBack is an interface which defines the methods ASP.NET server controls must implement to handle post back events.

To create a server control that captures the form submission information from the browser you must implement this interface.