navigaton_provider.dart

 Future<bool> onWillPop(BuildContext context) async {
    final currentNavigatorState = currentScreen.navigatorState.currentState;

    if (currentNavigatorState.canPop()) {
      currentNavigatorState.pop();
      return false;
    } else {
      if (currentTabIndex != FIRST_SCREEN) {
        setTab(FIRST_SCREEN);
        notifyListeners();
        return false;
      } else {
        return false;
        );
      }
    }
  }
//...