Flutter - How to change state from inside another widget

问题

I'm trying to implement both a Drawer and the Bottom Navigation Bar. The below class NavigationHomeScreen is my home screen and when the user clicks a menu item in the Drawer the Changeindex function updates the screenView I would like to know how I can similarly update the screenView but from the BottomNavigationBarApp using the onTabTapped method.

class NavigationHomeScreen extends StatefulWidget {
  @override
  _NavigationHomeScreenState createState() => _NavigationHomeScreenState();
}

class _NavigationHomeScreenState extends State<NavigationHomeScreen> {
  Widget screenView;
  DrawerIndex drawerIndex;

  @override
  void initState() {
    drawerIndex = DrawerIndex.HOME;
    screenView = const MyHomePage();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      color: AppTheme.nearlyWhite,
      child: SafeArea(
        top: false,
        bottom: false,
        child: Scaffold(
          appBar: emptyAppbar(),
          backgroundColor: AppTheme.nearlyWhite,
          body: DrawerUserController(
            screenIndex: drawerIndex,
            drawerWidth: MediaQuery.of(context).size.width * 0.75,
            onDrawerCall: (DrawerIndex drawerIndexdata) {
              changeIndex(drawerIndexdata);
              //callback from drawer for replace screen as user need with passing DrawerIndex(Enum index)
            },
            screenView: screenView,
            //we replace screen view as we need on navigate starting screens like MyHomePage, HelpScreen, FeedbackScreen, etc...
          ),
          bottomNavigationBar:BottomNavigationBarApp(context, 1),
        ),
      ),
    );
  }

  void changeIndex(DrawerIndex drawerIndexdata) {
    if (drawerIndex != drawerIndexdata) {
      drawerIndex = drawerIndexdata;
      if (drawerIndex == DrawerIndex.HOME) {
        setState(() {
          screenView = const MyHomePage();
        });
      } else if (drawerIndex == DrawerIndex.Help) {
        setState(() {
          screenView = HelpScreen();
        });
      } else if (drawerIndex == DrawerIndex.FeedBack) {
        setState(() {
          screenView = FeedbackScreen();
        });
      } else if (drawerIndex == DrawerIndex.Invite) {
        setState(() {
          screenView = InviteFriend();
        });
      } else {
        //do in your way......
      }
    }
  }
}

class BottomNavigationBarApp extends StatelessWidget {
  final int bottomNavigationBarIndex;
  final BuildContext context;

  const BottomNavigationBarApp(this. context, this.bottomNavigationBarIndex);

  void onTabTapped(int index) {

  }

  @override
  Widget build(BuildContext context) {
    return BottomNavigationBar(
      currentIndex: bottomNavigationBarIndex,
      type: BottomNavigationBarType.fixed,
      selectedFontSize: 10,
      selectedLabelStyle: TextStyle(color: CustomColors.BlueDark),
      selectedItemColor: CustomColors.BlueDark,
      unselectedFontSize: 10,
      items: [
        BottomNavigationBarItem(
          icon: Container(
            margin: EdgeInsets.only(bottom: 5),
            child: Image.asset(
              'assets/images/home.png',
              color: (bottomNavigationBarIndex == 1)
                  ? CustomColors.BlueDark
                  : CustomColors.TextGrey,
            ),
          ),
          title: Text('Home'),
        ),
        BottomNavigationBarItem(
          icon: Container(
            margin: EdgeInsets.only(bottom: 5),
            child: Image.asset(
              'assets/images/task.png',
              color: (bottomNavigationBarIndex == 0)
                  ? CustomColors.BlueDark
                  : CustomColors.TextGrey,
            ),
          ),
          title: Text('Appointments'),
        ),
      ],
      onTap: onTabTapped,
    );
  }
}

回答1:

You can pass a reference to a function down to a widget. Something like this:

In your HomeScreen:

 void updateScreenView() {
   //Do changes you want here. Dont forget to setState!
  }

In your BottomNavigationBarApp:

  final int bottomNavigationBarIndex;
  final BuildContext context;
  final function tapHandler;

  const BottomNavigationBarApp(this. context, this.bottomNavigationBarIndex, this.tapHandler);

and then just pass the reference on:

bottomNavigationBar:BottomNavigationBarApp(context, 1, updateScreenView),

And assign the function to your handler.

onTap: () => tapHandler(),

来源：https://stackoverflow.com/questions/61957723/flutter-how-to-change-state-from-inside-another-widget