login_screen.dart

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

class _LoginScreenState extends State<LoginScreen> {
  final FocusNode _uidFocusNode = FocusNode();

  Future<FirebaseApp> _initializeFirebase() async {
    FirebaseApp firebaseApp = await Firebase.initializeApp();

    return firebaseApp;
  }

  @override
  Widget build(BuildContext context) {
    // ...
  }
}