在仍然进入应用程序主页时，在颤振错误中未选择谷歌帐户登录中的帐户

Question

So implementing this google account sign in feature for the app that I'm building and i encounter this bug on which if i dont select an account like click outside the pop up selection of google account or press the back button i can still enter the home page of the app, i dont know how to catch this error please help me, this is my code

 ElevatedButton.icon(
                                style: ElevatedButton.styleFrom(
                                  primary: Colors.white,
                                  onPrimary: Colors.black,
                                  minimumSize: const Size(double.infinity,50),
                                ),
                                icon: const FaIcon(FontAwesomeIcons.google, color: Colors.red,),
                                label: const Text("Login using Gmail"),
                                onPressed: () async{
                                  
                                  try {
                                    var result = await FirebaseServices().signInWithGoogle()..catchError((onError) => print(onError.toString()));

                                    if (result == null) return;
                                    
                                    Navigator.push(context, MaterialPageRoute(builder: (context)=> const HomePage()));
                                    
                                  // if (FirebaseServices().signInWithGoogle() == null) return;
                                  // Navigator.push(context,MaterialPageRoute(builder: (context)=> const HomePage()));
                                  
                                  }
                                  on FirebaseAuthException catch (e){
                                    print(e.message);
                                    throw e;
                                    }
                                },
                              ),

and here's my main.dart code

class _MyAppState extends State<MyApp> {

  late StreamSubscription<User?> user;
  @override
  void initState() {
    super.initState();
    user = FirebaseAuth.instance.authStateChanges().listen((user) {
      if (user == null) {

        print('User is currently signed out!');
      } else {
        print('User is signed in!');
      }
    });
  }

  @override
  void dispose() {
    user.cancel();
    super.dispose();
  }

  @override

  Widget build(BuildContext context) {
    return GetMaterialApp(
        initialRoute:
        // "/loginpage",

        FirebaseAuth.instance.currentUser == null ? LoginPage.id : HomePage.id,
        routes: {
          // "/homepage": (context)=> const HomePage(),
          // "/loginPage" : (context)=> const LoginPage(),
          
          LoginPage.id: (context) =>const LoginPage(),
          HomePage.id: (context) => const HomePage(),
          
        },
        home: const LoginPage(),
      );
    
  }

  
}

and here's my google service code

class FirebaseServices{
  final _auth = FirebaseAuth.instance;
  final _googleSignIn = GoogleSignIn();
  final _formkey = GlobalKey<FormState>();

var context;

  signInWithGoogle() async{
    //if(_formkey.currentState!.validate()){
      try{
      final GoogleSignInAccount? googleSignInAccount =
          await _googleSignIn.signIn().catchError((onError)=>print(onError));
          //plugin
          if (googleSignInAccount == null) return null;
          // ignore: unused_local_variable
          final GoogleSignInAuthentication googleSignInAuthentication = await googleSignInAccount.authentication;
          //end plugin
      if (googleSignInAccount!=null){
        final GoogleSignInAuthentication googleSignInAuthentication =
            await googleSignInAccount.authentication;
        final AuthCredential authCredential = GoogleAuthProvider.credential(
          accessToken: googleSignInAuthentication.accessToken,
            idToken: googleSignInAuthentication.idToken);
        await _auth.signInWithCredential(authCredential)
            .then((value) => {
          postDetailsToFirestore(),
        }
        ).catchError((e)
        {
          Fluttertoast.showToast(msg: e!.message);
        });
       
      }
    }on FirebaseAuthException catch (e){
      print(e.message);
      throw e;
    //}

    }
    
    
  }

  signOut() async{
    await _auth.signOut();
    await _googleSignIn.signOut();
  }
  postDetailsToFirestore() async{

    //calling firestore,calling user model, sending values

    FirebaseFirestore firebaseFirestore = FirebaseFirestore.instance;
    User? user = _auth.currentUser;

    UserModel userModel = UserModel();

    //writing values
    userModel.email = user!.email;
    userModel.uid = user.uid;
    userModel.fullname = user.displayName;
    userModel.profileimage=user.photoURL;


    await firebaseFirestore
        .collection("Users")
        .doc(user.uid)
        .set(userModel.toMap());

    
  }
} 

here's a video about the bug here's the newest bug

Answer 1

The logic in your "onPressed" login button should only authenticate, but not push the homePage.

The recommended solution is to have a "landingPage" listening to FirebaseAuth.instance.authStateChanges() and checking the user. If it is null, push AuthenticationPage, otherwise homePage.

You can find more details below:

https://firebase.google.com/docs/auth/flutter/start

https://pub.dev/packages/google_sign_in/example (this example listens to a different stream) but has the same logic

Answer 2

When you are first calling the FirebaseServices.signInWithGoogle().catchError(); You are awaiting an error result. I would suggest you that you call it in this way:

try {
    // Here, we use the .. (cascade) operator, which will give us the
    // reference to the correct future that signInWithGoogle() returns.
    var result = await FirebaseServices().signInWithGoogle()..catchError((onError) => print(onError.toString()));

    // If we didn't sign in, then do not proceed to the home screen
    if (result == null) return;

    // We push a replacement route so that when the user 
    // consecutively presses the back button, he doesn't reach the
    // login screen before exiting the app.
    Navigator.pushReplacement(context, MaterialPageRoute(builder: (context)=> const HomePage()));
} on FirebaseAuthException catch(e) {
    print(e.message);
    // Do not throw an exception in your production app. It will make the app crash. Instead, 
    // display it to the user with a Dialog.
    throw e;
}

If my answer was helpful, please mark my answer as Correct. Thank you!

Also, I recommend you to follow @Saichi Okuma's answer, as that is the correct approach to signing-in the user in a production app.