[FIXED] How to check if the user is logged in, if so show other screen?

Issue

My first screen is a login screen and it needs to check if the user is logged in to open the home screen directly but I get an error using this check.

I’m doing the check on initState, the condition is returning true, so looks like the problem is with the Navigator.

What is the correct way to skip the first screen if the user is logged in?

Error:

I/flutter (20803): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (20803): The following assertion was thrown building Navigator-[GlobalObjectKey<NavigatorState>
I/flutter (20803): _WidgetsAppState#8ce27](dirty, state: NavigatorState#db484(tickers: tracking 2 tickers)):
I/flutter (20803): 'package:flutter/src/widgets/navigator.dart': Failed assertion: line 2106 pos 12: '!_debugLocked':
I/flutter (20803): is not true.
I/flutter (20803): Either the assertion indicates an error in the framework itself, or we should provide substantially
I/flutter (20803): more information in this error message to help you determine and fix the underlying cause.

Code:

class LoginScreen extends StatefulWidget {
  @override
  _LoginScreenState createState() => _LoginScreenState();
}

class _LoginScreenState extends State<LoginScreen> {


  final _emailController = TextEditingController();
  final _passController = TextEditingController();

  final _formKey = GlobalKey<FormState>();
  final _scaffoldKey = GlobalKey<ScaffoldState>();

  @override
  void initState() {
    super.initState();

    if(FirebaseAuth.instance.currentUser() != null){

      Navigator.of(context).pushReplacement(MaterialPageRoute(
        builder: (context) => HomeScreen()
      ));
    }

  }


  @override
  Widget build(BuildContext context) {

    return Scaffold(
      key: _scaffoldKey,
      body: ScopedModelDescendant<UserModel>(
          builder: (context, child, model){

            if(model.isLoading)
              return Center(
                child: CircularProgressIndicator(),
              );

            return Form(
              key: _formKey,
              child: ListView(
                padding: EdgeInsets.all(16),
                children: <Widget>[
                  SizedBox(height: 67),
                  Icon(Icons.chrome_reader_mode, size: 150, color: Colors.blue,),
                  SizedBox(height: 16,),
                  TextFormField(
                    controller: _emailController,
                    decoration: InputDecoration(
                        hintText: "Digite seu e-mail",
                        border: OutlineInputBorder(
                            borderRadius: BorderRadius.circular(10),
                        ),
                      fillColor: Colors.blueAccent
                    ),
                    keyboardType: TextInputType.emailAddress,
                    validator: (text){
                      if(text.isEmpty || !text.contains("@"))
                        return "E-mail inválido!";
                    },
                  ),
                  SizedBox(height: 16,),
                  TextFormField(
                    controller: _passController,
                    decoration: InputDecoration(
                        hintText: "Digite sua senha",
                        border: OutlineInputBorder(
                          borderRadius: BorderRadius.circular(10),
                        ),
                        fillColor: Colors.blueAccent
                    ),
                    obscureText: true,
                    validator: (text){
                      if(text.isEmpty || text.length < 6)
                        return "Digite a senha!";
                    },
                  ),
                  SizedBox(height: 16,),
                  FlatButton(
                    padding: EdgeInsets.all(13),
                    shape: RoundedRectangleBorder(
                        borderRadius: BorderRadius.circular(10)
                    ),
                    color: Colors.blue,
                      child: Text("Entrar",
                        style: TextStyle(
                          color: Colors.white,
                          fontSize: 20
                        ),
                      ),
                      onPressed: (){

                          if(_formKey.currentState.validate()){

                            model.signIn(

                              email: _emailController.text,
                              pass: _passController.text,
                              onSuccess: _onSuccess,
                              onFail: _onFail,

                            );

                          }


                      },
                  ),
                  SizedBox(height: 10,),
                  InkWell(
                    onTap: (){

                      if(_emailController.text.isEmpty || !_emailController.text.contains("@")){

                        _scaffoldKey.currentState.showSnackBar(
                            SnackBar(content: Text("Insira um e-mail válido para recuperação",
                              style: TextStyle(fontSize: 14),
                            ),
                              backgroundColor: Colors.redAccent,
                              duration: Duration(seconds: 3),
                            )
                        );

                      } else {
                         model.recoverPass(_emailController.text);
                         _scaffoldKey.currentState.showSnackBar(
                           SnackBar(
                             content: Text("O e-mail de recuperação foi enviado!",
                               style: TextStyle(fontSize: 14),
                             ),
                             backgroundColor: Colors.green,
                             duration: Duration(seconds: 3),
                           )
                         );
                      }

                    },
                    child: Text("Esqueci minha senha",
                      style: TextStyle(
                          color: Colors.black,
                          fontSize: 16,
                          fontWeight: FontWeight.w400
                      ),
                      textAlign: TextAlign.center,

                    ),
                  ),
                  SizedBox(height: 30,),
                  InkWell(
                    onTap: (){

                      Navigator.of(context).push(MaterialPageRoute(
                          builder: (context)=> SignUpScreen())
                      );

                    },
                    child: Text("Não tem conta? Cadastre-se!",
                      style: TextStyle(
                        color: Colors.black,
                        fontSize: 16,
                        fontWeight: FontWeight.w600
                      ),
                      textAlign: TextAlign.center,

                    ),
                  ),
                ],
              ),
            );

          },
      ),


    );
  }




}

Solution

Well you can solve this kind of problem using another approach. Instead check if there is user logged inside your loginScreen class you can do this a step before and then decide if you will show the loginScreen if there is no user logged or show another screen, MainScreen I’ am supposing, if the user is already logged.

I will put some snipet showing how to accomplish this. I hope it helps. But before I will explain you what is wrong in your source code.

if(FirebaseAuth.instance.currentUser() != null){
      // wrong call in wrong place!
      Navigator.of(context).pushReplacement(MaterialPageRoute(
        builder: (context) => HomeScreen()
      ));
}

Your code is broken because currentUser() is a async function and when you make the call this function is returning a incomplete Future object which is a non null object. So the navigator pushReplacement is always been called and it’s crashing because the state of your widget is not ready yet.

Well as solution you can user FutureBuilder and decide which screen you will open.

int main(){
   runApp(  YourApp() )
}

class YourApp extends StatelessWidget{

    @override
    Widget build(BuildContext context){
        return FutureBuilder<FirebaseUser>(
            future: FirebaseAuth.instance.currentUser(),
            builder: (BuildContext context, AsyncSnapshot<FirebaseUser> snapshot){
                       if (snapshot.hasData){
                           FirebaseUser user = snapshot.data; // this is your user instance
                           /// is because there is user already logged
                           return MainScreen();
                        }
                         /// other way there is no user logged.
                         return LoginScreen();
             }
          );
    }
}

Using this approach you avoid your LoginScreen class to verify if there is a user logged!

As advise you can make use of snapshot.connectionState property with a switch case to implement a more refined control.

Answered By – Marcos Boaventura

Answer Checked By – Katrina (Easybugfix Volunteer)

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