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

Question

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)

Jesuitism

each form should have only one child as i know – Raneeraney

Try to Add Key on ListView,GridView SingleChildScrollView etc.. this will solve the issue as you are using the same key for two Scroll Widget – Encore

I add key all the ListView, GridView, SingleChildScrollView but it didnt solve it. @ArunR.Prajapati – Jesuitism

@MuratAslan Form already has only one child which is a column – Klehm

one textfield i mean – Raneeraney

@MuratAslan So you're saying: "Each form should have only one textformfield widget". That's simply not the case and not how the forms work. Please review some form examples with Flutter medium.com/flutter-community/… – Klehm

Hot Restart. Most errors are due to changes made – Authority

Add home property in main.dart file... – Futuristic

Answer 1

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

Dramatics

this can't be a solution. App must need a hot reload or restart – Spunk

It does work @Mukta, try this option only once untill your problem gets resolved. Mine did – Scaffold

Still you don't have any idea about Global Key of Flutter. Notice the question. He is using a single key for multiple Widget or Screen. Either he needs to use a list of Global keys or different naming single key. Still now I am disagree with your answer. Sorry – Spunk

Answer 2

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(),
      },
    );
  }
}

Chingchinghai

Answer 3

i just stopped the hot reload and restarted the app it worked for me

Walkling

This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review – Spectroscope

Answer 4

In case you are getting the error when the app just started: Add '/' route to the list of routes and restart.

Gut

Answer 5

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(),
    );
  }
}

Devastation

Answer 6

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

Nabokov

Answer 7

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

Shiekh

it dosn't effect on code. But obviously need to declare as final. – Spunk

Answer 8

just kill the app run (stop) and uninstall it then reinstall it again to reset the navigator state

Chen

Answer 9

Just assign UniqueKey() to your ListView.

Rosina

Answer 10

in my case i was forgot add async await for main()

main() async {
  await initModul();
  runApp(MyApp());
}

initModul() async {
  WidgetsFlutterBinding.ensureInitialized();

  final SharedPreferences sharedPreferences =
      await SharedPreferences.getInstance();

  instance.registerLazySingleton<SharedPreferences>(
    () => sharedPreferences,
  );

  instance.registerLazySingleton<AppSettingsSharedPreferences>(
      () => AppSettingsSharedPreferences(instance()));

  // for clear preferences:
  // AppSettingsSharedPreferences appSettingsSharedPreferences =
  // instance<AppSettingsSharedPreferences>();
  // appSettingsSharedPreferences.clear();
}

Oglesby

Answer 11

This link may help you. You need to either remove / prefix from your route names or your root route with / should be pushed before pushing current route.

https://medium.com/codechai/dont-use-to-prefix-your-routes-in-flutter-f3844ce1fdd5

Entomophilous

Answer 12

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.

Triple