Authentication Flow with Flutter - flutter

Question

I'm new to flutter. I am trying to set up an authentication flow. if the user is not logged in, I plan to build a MaterialApp with certain routes (eg Facebook Auth, Google Auth and Email Auth). If the user is logged in, they ll see another MaterialApp with routes such as HomePage, ListPage, CreatePage etc.
I tried but below codes fail. Anyone with experience can advise? thanks in advance
import 'package:flutter/material.dart';
import 'package:scoped_model/scoped_model.dart';
import './pages/email.dart';
import './pages/auth.dart';
import './pages/home.dart';
import './pages/list.dart';
import './pages/create.dart';
import './scoped-models/main.dart';
void main() => runApp(new MyApp());
class MyApp extends StatefulWidget {
#override
State<StatefulWidget> createState() {
return _MyAppState();
}
}
class _MyAppState extends State<MyApp> {
final MainModel _model = MainModel();
bool _isAuthenticated = false;
#override
void initState() {
_model.autoAuthenticate();
_model.userSubject.listen((bool isAuthenticated) {
setState(() {
_isAuthenticated = isAuthenticated;
});
});
super.initState();
}
#override
Widget build(BuildContext context) {
print(_isAuthenticated);
return ScopedModel<MainModel>(
model: _model,
child: !_isAuthenticated == true
? MaterialApp(
theme: ThemeData(
primaryColor: Colors.lime, buttonColor: Colors.teal),
routes: {
'/': (BuildContext context) => AuthPage(),
'/email': (BuildContext context) => EmailPage(),
},
)
: MaterialApp(
theme: ThemeData(
primaryColor: Colors.lime, buttonColor: Colors.teal),
routes: {
'/': (BuildContext context) => HomePage(),
'/list': (BuildContext context) => ListPage(),
'/create': (BuildContext context) => CreatePage()
},
),
);
}