flutter error LateInitializationError: Field '@' has not been initialized

Question

This is the middle part of the main that is expected to cause the error. If you are not logged in on the splash screen, this code goes to MyHomePage and logs in. If you are logged in, it goes to MainScreen and switches to the main screen of the app.

  class SplashScreen extends StatefulWidget {
      @override
      _SplashScreenState createState() => _SplashScreenState();
    }
    
    class _SplashScreenState extends State<SplashScreen> {
    
      final FirebaseAuth auth = FirebaseAuth.instance;
      final User? user = FirebaseAuth.instance.currentUser;
    
      @override
      void initState() {
        super.initState();
        _initUser().whenComplete((){
          setState(() {});
        });
      }
    
      _initUser() async {
        if (auth.currentUser != null) {
          Timer(
            Duration(seconds: 2),
                () => Navigator.of(context).pushAndRemoveUntil(
                    MaterialPageRoute(
                        builder: (context) =>
                            MainScreen(user!)),
                        (Route<dynamic> route) => false),
          );
        } else {
          Timer(Duration(seconds: 1),
                  () => Navigator.of(context).pushAndRemoveUntil(
                      MaterialPageRoute(
                          builder: (context) =>
                              MyHomePage()),
                          (Route<dynamic> route) => false),
          );
        }
      }
    
      @override
      Widget build(BuildContext context) {
    
        return Scaffold(
            body: Center(
              child: Text("Splash Screen"),
            ),
    
        );
      }
    }

This is the MyHomePage widget that is passed when you are not logged in.

class MyHomePage extends StatefulWidget {
      const MyHomePage({Key? key}) : super(key: key);
    
      @override
      State<MyHomePage> createState() => _MyHomePageState();
    }
    
    class _MyHomePageState extends State<MyHomePage> {
    
      @override
      Widget build(BuildContext context) {
        return Scaffold(
          body: Center(
            child: TextButton(
              onPressed: (){
    
                FirebaseService().signup(context);
              },
              child: Text('Google'),
            ),
          )
        );
      }
    }
    class FirebaseService{
    
      final FirebaseAuth auth = FirebaseAuth.instance;
      final GoogleSignIn googleSignIn = GoogleSignIn();
    
      Future<void> signup(BuildContext context) async {
    
    
      final GoogleSignInAccount? googleSignInAccount = await googleSignIn.signIn();
      if (googleSignInAccount != null) {
        final GoogleSignInAuthentication googleSignInAuthentication =
        await googleSignInAccount.authentication;
        final AuthCredential authCredential = GoogleAuthProvider.credential(
            idToken: googleSignInAuthentication.idToken,
            accessToken: googleSignInAuthentication.accessToken);
    
        // Getting users credential
        UserCredential result = await auth.signInWithCredential(authCredential);
        User? user = result.user;
    
    
        if (user != null) {
          Navigator.push(
              context, MaterialPageRoute(builder: (context) => MainScreen(user)));
        }  // if result not null we simply call the MaterialpageRoute,
        // for go to the HomePage screen
      }
    }
    
      Future<void> signOutFromGoogle() async{
        await googleSignIn.signOut();
        await auth.signOut();
      }
    }

This is the content of the error

The following LateError was thrown building MainScreen(dirty, dependencies: [_InheritedProviderScope<Pro?>], state: _MainScreenState#d95a0):
LateInitializationError: Field '_instance@640075166' has not been initialized.

The relevant error-causing widget was: 
  MainScreen MainScreen:file:///F:/flutter%20project/good_man/lib/main.dart:75:25
When the exception was thrown, this was the stack: 

Sorry, I forgot the mainscreen code. Below is the mainscreen code

class MainScreen extends StatefulWidget {
  const MainScreen(this.user);

  final User user;

  @override

  _MainScreenState createState() => _MainScreenState();
}
class _MainScreenState extends State<MainScreen> {
  @override
  Widget build(BuildContext context) {

    final User user = widget.user;
    final pro = Provider.of<Pro>(context);
    return DefaultTabController(
      length: 3,
      child: Scaffold(

          appBar: PreferredSize(
              preferredSize: Size.fromHeight(60.0), // here the desired height
              child: AppBar(
                iconTheme: IconThemeData(color: Colors.black),
                backgroundColor: pro.backColor_main,
                elevation: 0.0,
                centerTitle: true,
                title: Text('aaa',
                  style: TextStyle(
                      fontFamily: 'Gugi',
                      fontSize: 20.sp,
                      color: Colors.black,
                  ),),
              ),
          ),
          drawer: Drawer(
            child: ListView(
              padding: EdgeInsets.zero,
              children: [
                DrawerHeader(
                  child: Text('Drawer Header'),
                  decoration: BoxDecoration(
                    color: Colors.white
                  ),
                ),
                ListTile(
                  title: Text('aaa'),
                  onTap: () {
                    Navigator.pop(context);
                  },
                ),

              ],
            ),
          ),
          bottomNavigationBar: BottomBar(),
          body: Stack(children:  [

            TabBarView(
              children:  [
                MainTest(),
                Text(''),
                Main_User(user),
              ],
            ),
          ])),
    );
  }
}

Sorry for posting all the code. There is no part that uses late , but the error code is displayed as late, and I try to delete the caches and start

Answer 1

Don't initialise the async task into the initState. Because of Flutter Life Cycle it can not await the flow... For more about the lIfe Cycle please visit this: Life Cycle of Widget

So Solution is... Use the FutureBuilder for awaiting the widget....

class SplashScreen extends StatefulWidget {
  @override
  _SplashScreenState createState() => _SplashScreenState();
}

class _SplashScreenState extends State<SplashScreen> {

  final FirebaseAuth auth = FirebaseAuth.instance;
  final User? user = FirebaseAuth.instance.currentUser;


  _initUser() async {
    if (auth.currentUser != null) {
      Timer(
        Duration(seconds: 2),
            () => Navigator.of(context).pushAndRemoveUntil(
            MaterialPageRoute(
                builder: (context) =>
                    MainScreen(user!)),
                (Route<dynamic> route) => false),
      );
    } else {
      Timer(Duration(seconds: 1),
            () => Navigator.of(context).pushAndRemoveUntil(
            MaterialPageRoute(
                builder: (context) =>
                   MyHomePage() ),
                (Route<dynamic> route) => false),
      );
    }
  }

  @override
  Widget build(BuildContext context) {

    return Scaffold(
      body: FutureBuilder(
        future: _initUser(),
        builder: (context, snapshot) {
          if(snapshot.hasData){
            //You you finish the initialization
            return Text("You Get the Data");
          }
          //Until the data get
          return Center(child: Text("Splash Screen"),);
        },
      ),

    );
  }
}

Answer 2

Actually error is in Initialisation of current user... You have to understand Life cycle of stateful widget... initState is not holding flow. it just initialise some some instance value...And you try to delay for 2 sec... So that's the issue.

Use FutureBuilder for _initUser() and when it fetch all data then proceed for the next screen.