The hardware Back button is analogous to the Back button on a web browser. However, when the user presses the Back button, past the first page of a phone app, the app is closed. This is in contrast to the phone’s hardware start button, which merely causes an app to be deactivated.
The hardware Back button should not be used for application-specific behavior. It is only for navigation, and if used otherwise, may cause your app to fail Windows Phone Marketplace certification.
To determine whether navigation is occurring because the hardware Back button was pressed or the navigation was initiated by a call to
NavigationService.GoBack, use the
NavigatingEventArgs.NavigationMode property as shown: