1. override
void didStopListening()

Called when the number of listeners changes from one to zero.

Source 

@override
void didStopListening() {
  first.removeListener(_maybeNotifyListeners);
  first.removeStatusListener(_maybeNotifyStatusListeners);
  next.removeListener(_maybeNotifyListeners);
  next.removeStatusListener(_maybeNotifyStatusListeners);
}