Called when the dialog has detected the user's press of the back
key.
Syntax
[Android.Runtime.Register("onBackPressed", "()V", "GetOnBackPressedHandler")] public virtual voidOnBackPressed ()
Remarks
Called when the dialog has detected the user's press of the back
key. The default implementation simply cancels the dialog (only if
it is cancelable), but you can override this to do whatever you want.