Flutter Stream Builder Triggered when Navigator Pop or Push is Called

Question

I have a stream builder in the app\'s home/root page. This stream builder gets triggered whenever I do a page-navigation elsewhere, which has nothing to do with the stream i

Answer 1

I spend hours figuring out how to fix this. Turns out AppHomePage need to extend StatefulWidget instead of StatelessWidget.

No idea why, but it works.

Answer 2

I can confirm that the build method in StreamBuilder is called every time we navigate within our app, which is not efficient since it should cancel its listener, create a new one and rebuild the entire widget.

You may face that issue if your app listens to the authentication state in order to show an appropriate screen when auth state changes (Loading/Login/Home)

So in most of the tutorials, you will see that StreamBuilder is created in the build method in a Stateless widget. This is not an efficient solution.

Instead use Stateful widget and listen to your auth changes in initState() or didChangeDependencies() methods.

The difference in our case would be that in initState() you will have issues in getting your Auth service if you use Provider (The context won't be ready with the Provided service yet). If you don't use Provider you can listen to changes in the initState(). But I highly recommend using Provider to separate your Services and Pages. In other words, use the MVVM pattern so your code will be scalable and maintainable.

class LandingScreen extends StatefulWidget {
  @override
  _LandingScreenState createState() => _LandingScreenState();
}

class _LandingScreenState extends State<LandingScreen> {
  @override
  Widget build(BuildContext context) {
      return SplashView();
  }

  @override
  void didChangeDependencies() {
      //we don't have to close or unsubscribe SB
        Provider.of<AuthService>(context, listen: false).streamAuthServiceState().listen((state){
          switch (state) {
            case AuthServiceState.Starting:
            print("starting");
              break;
            case AuthServiceState.SignedIn:
              Navigator.pushReplacementNamed(context, Routes.HOME);
              break;
            case AuthServiceState.SignedOut:
              Navigator.pushReplacementNamed(context, Routes.LOGIN);
              break;
            default:
              Navigator.pushReplacementNamed(context, Routes.LOGIN);
          }
        });

    super.didChangeDependencies();
  }
}

If you'll use directly Firebase stream - replace my stream with FirebaseAuth.instance.onAuthStateChanged