error: Invalid constant value. while setting global key for scaffoldMessengerKey

Question

i wanted to use snackbar without Scaffold . found many similar question doing this same thing but its not working for me for some reason.

    Future<void> main() async {
      await dotenv.load(fileName: '.env');
      runApp(const HomeScreens());
    }
      class HomeScreens extends StatefulWidget {
  const HomeScreens({Key? key}) : super(key: key);

  @override
  _HomeScreensState createState() => _HomeScreensState();
}

class _HomeScreensState extends State<HomeScreens> {
  late final GlobalKey<ScaffoldMessengerState>? scaffoldMessengerKey;
  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider(
     create:(BuildContext context) => MyCurrentTrack(),
      child: const MaterialApp(
        scaffoldMessengerKey: scaffoldMessengerKey, // <= this
        home: LoginScreen(),
        debugShowCheckedModeBanner: false,
      ),
    );
  }
}

and also tried this one too but its the same error always

class _HomeScreensState extends State<HomeScreens> {
  final GlobalKey<ScaffoldMessengerState> rootScaffoldMessengerKey = GlobalKey<ScaffoldMessengerState>();

  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider(
     create:(BuildContext context) => MyCurrentTrack(),
      child: const MaterialApp(
        scaffoldMessengerKey: rootScaffoldMessengerKey, // <= this
        home: LoginScreen(),
        debugShowCheckedModeBanner: false,
      ),
    );
  }
}

Answer 1

Your material app is no longer constant, because it takes a variable as a parameter. a const value must be unchanging and defined at runtime. Your material app can't be constant anymore, you need to remove the const keyword:

  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider(
     create:(BuildContext context) => MyCurrentTrack(),
      // child: const MaterialApp(
      child: MaterialApp( // no const keyword
        scaffoldMessengerKey: rootScaffoldMessengerKey,
        home: LoginScreen(),
        debugShowCheckedModeBanner: false,
      ),
    );
  }