Flutter firebase auth doesn't persist after app is killed - firebase

Question

I am trying to persist the firebase auth state in a flutter app by using this code from the documentation but when I kill the app in the emulator and open it again it doesn't recognize a user.
I can use sharedpreferences but I want to use only firebase, what am I doing wrong here?
main.dart
void main() async {
WidgetsFlutterBinding.ensureInitialized();
await Firebase.initializeApp();
runApp(MyApp());
}
class MyApp extends StatelessWidget {
// Create the initialization Future outside of `build`:
final Future<FirebaseApp> _initialization = Firebase.initializeApp();
final FirebaseAuth auth = FirebaseAuth.instance;
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return FutureBuilder(
// Initialize FlutterFire:
future: _initialization,
builder: (context, snapshot) {
// Check for errors
if (snapshot.hasError) {
return (MaterialApp(
home: Warning(
warning: 'Error',
),
));
}
// once complete show your app
if (snapshot.connectionState == ConnectionState.done) {
print('CONNECTED');
if (AuthService().user() == null) {
return MaterialApp(
home: LoginPage(),
);
} else {
return MaterialApp(
home: HomePage(),
);
}
}
// if nothing happens return loading
return MaterialApp(
home: //LoginPage()
Warning(
warning: 'Loading',
),
);
},
);
}
}
AuthService class
import 'package:firebase_auth/firebase_auth.dart';
class AuthService {
final FirebaseAuth _auth = FirebaseAuth.instance;
// auth change user stream
User user() {
// ignore: deprecated_member_use
_auth.authStateChanges().listen((User user) {
if (user == null) {
return null;
} else {
return user;
}
});
}
}
I hope you can help me to understand the problem and solve it, thank you.

Answer 1

Since authStateChanges returns a Stream, you'll want to use a StreamBuilder in your code to wrap that asynchronous operation too.
Something like this:
// once complete show your app
if (snapshot.connectionState == ConnectionState.done) {
print('CONNECTED');
return StreamBuilder(
stream: FirebaseAuth.instance. authStateChanges(),
builder: (BuildContext context, snapshot) {
if (snapshot.hasData) {
return MaterialApp(
home: LoginPage(),
);
} else {
return MaterialApp(
home: HomePage(),
);
}
}
)
}
Unrelated: you're repeated the code to create a MaterialApp quite frequently, which is not needed. For example, in the above snippet we could have only one mention of MaterialApp and get the same result with:
// once complete show your app
if (snapshot.connectionState == ConnectionState.done) {
print('CONNECTED');
return StreamBuilder(
stream: FirebaseAuth.instance. authStateChanges(),
builder: (BuildContext context, snapshot) {
return MaterialApp(
home: snapshot.hasData && snapshot.data != null ? HomePage() : LoginPage(),
)
}
)
}
If you do this for all mentions of MaterialApp and other duplication, you can reduce the code significantly, making it less error prone and easier to maintain.

Answer 2

It does persist. You are just not using the auth state listener correctly. The return statements from your authStateChanges listener are not actually escaping the call to user(). On top of that, the listener could return null the first time. It's not until some time later that the Firebase SDK determines that the user is actually valid and signed in. Your listener will get a second callback at that time. Your code need to be ready for this to happen - it can't just blindly take the first value, as the auth state might change over time.
I suggest adding some debug logging in your auth state listener to see how this actually works. Also I suggest reading this blog to understand how auth state listeners work in more detail.

Answer 3

You can use my code, You can use userChanges() instead of authStateChanges()
final Stream<User?> firebaseUserChanges = firebaseAuth.userChanges();