检查 Firebase uID 然后路由

Question

So my main.dart looking like this, I just want to check if the user already loggedIn or not. If true then route him directly to Homescreen and passing the UID else to the SignIn screen.

But somehow im getting a black screen without any error. Why? the debug print statements are working...

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

//User logged in?
final FirebaseAuth auth = FirebaseAuth.instance;
final User? user = auth.currentUser;

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    FirebaseAuth.instance.authStateChanges().listen((User? user) {
      if (user == null) {
        print('User is currently signed out!');
        MaterialPageRoute(builder: (context) => const SignIn());
      } else {
        String myUid = user.uid;
        MaterialPageRoute(builder: (context) => HomeScreen(userId: myUid));
        print('User is signed in!');
      }
    });
    return const SizedBox.shrink(); //<-----here
  }
}

Well my Code looking now like this:

    Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

//User logged in?
final FirebaseAuth auth = FirebaseAuth.instance;

//The stream for auth changee
Future<User?> data() async {
  return FirebaseAuth.instance.currentUser;
}

final User? user = auth.currentUser;

class MyApp extends StatelessWidget {
  MyApp({Key? key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return StreamBuilder<User?>(
        stream: FirebaseAuth.instance
            .authStateChanges(), //FirebaseAuth.instance.authStateChanges(),
        builder: (context, snapshot) {
          if (snapshot.hasError) {
            return const Text('Something went wrong');
          }
          if (snapshot.connectionState == ConnectionState.waiting) {
            return const Text("Loading");
          }

          if (snapshot.connectionState == ConnectionState.active) {
            if (user == null) {
              print('User is currently signed out!');
              Navigator.push(context,
                  MaterialPageRoute(builder: (context) => const SignIn()));
            } else {
              String myUid = user!.uid;
              Navigator.push(
                  context,
                  MaterialPageRoute(
                      builder: (context) => HomeScreen(
                            userId: myUid,
                          )));
            }
          }
          return const CircularProgressIndicator();
        });
  }
}

Navigator operation requested with a context that does not include a Navigator. The relevant error-causing widget was StreamBuilder<User?>

Answer 1

You can't just insert a stream listener in the build method like that. The easiest way to do this, is to use a StreamBuilder which handles the stream for you. Similar to the example in the documentation on listening for Firestore updates that'd be something like:

StreamBuilder<User?>(
  stream: FirebaseAuth.instance.authStateChanges(),
  builder: (BuildContext context, AsyncSnapshot<User?> snapshot) {
    if (snapshot.hasError) {
      return const Text('Something went wrong');
    }

    if (snapshot.connectionState == ConnectionState.waiting) {
      return const Text("Loading");
    }

    if (user == null) {
      print('User is currently signed out!');
      return MaterialPageRoute(builder: (context) => const SignIn());
    } else {
      String myUid = user.uid;
      return MaterialPageRoute(builder: (context) => HomeScreen(userId: myUid));
    }
  },