A global key was used multiple times inside one widgets child list

After closing the app, when I try to open it again, I'm getting the following error but it's only on iOS platform, Android works well.

I have looked around and there are several SO questions and issues about this problem but I couldn't solve it. I'm also using bloc pattern for managing state.

I have GlobalKey<FormState> in my AuthenticateForm.

import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:low_code/blocs/authentication/authentication_bloc.dart';
import 'package:low_code/blocs/authentication/authentication_event.dart';
import 'package:low_code/helpers/app_localization/app_localizations.dart';

class AuthenticateForm extends StatefulWidget {
  @override
  _AuthenticateFormState createState() => _AuthenticateFormState();
}

class _AuthenticateFormState extends State<AuthenticateForm> {
  GlobalKey<FormState> _formKey = GlobalKey<FormState>();

  String username;

  String password;

  @override
  Widget build(BuildContext context) {
    AppLocalizations appLocalizations = AppLocalizations.of(context);
    return Form(
      key: _formKey,
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.stretch,
        children: <Widget>[
          TextFormField(
            onSaved: (String value) => username = value,
            initialValue: 'dms-bpm',
            decoration: InputDecoration(
                labelText: appLocalizations.translate('username')),
            // ignore: missing_return
            validator: (String value) {
              if (value.isEmpty) {
                return 'Please enter your ${appLocalizations.translate('username')}';
              }
            },
          ),
          TextFormField(
            onSaved: (String value) => password = value,
            obscureText: true,
            decoration: InputDecoration(
                labelText: appLocalizations.translate('password')),
            initialValue: 'dms-bpm',
            // ignore: missing_return
            validator: (String value) {
              if (value.isEmpty) {
                return 'Please enter your ${appLocalizations.translate('password')}';
              }
            },
          ),
          RaisedButton(
            shape: RoundedRectangleBorder(
                borderRadius: BorderRadius.all(Radius.circular(15))),
            child: Text(appLocalizations.translate('login')),
            onPressed: () {
              _formKey.currentState.save();
              if (_formKey.currentState.validate()) {
                BlocProvider.of<AuthenticationBloc>(context)
                  ..dispatch(
                      Authenticate(username: username, password: password));
              }
            },
          )
        ],
      ),
    );
  }
}

Flutter (Channel stable, v1.7.8+hotfix.4, on Microsoft Windows [Version 10.0.17763.615], locale en-GB)

Solution 1: live-love

In my case this error happened because I had a initialRoute property set, while instead I should set the home property:

class RouteTestApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Demo',
      //initialRoute: '/', //remove this
      home: FirstScreen(),  //this is the calling screen
      routes: {
        ExtractArgumentsScreen.routeName: (context) => ExtractArgumentsScreen(),
      },
    );
  }
}

Solution 2: Rezaul Islam

In my case, I run the flutter app without adding home: BottomNavBar(). after getting an error I added home: BottomNavBar() and give hot reload (Command + s) which reproduce this error (A global key was used multiple times inside one widget child list). Then I just reconnect my target device and run again, which fixed my issue.

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        brightness:Brightness.light,
        primaryColor: Colors.white,
        accentColor: Colors.blue,
        fontFamily: 'Poppins',
        appBarTheme: AppBarTheme(
          centerTitle: true,
        ),
      ),
      home: BottomNavBar(),
    );
  }
}

Solution 3: Collen Zhou

Try stop and rerun you application instead of hot reloading. That solved my problem.

Solution 4: Fernando Batista

Try to make your GlobalKey "final". I think the fact your global key is mutable might be creating this problem.

Solution 5: Macdonald

In my case, the calling screen in the home: property of the MaterialApp() object was returning null. After fixing it, I stopped the app and reran it.