why it doesn't keep the user logged in - firebase

Question

it doesnt matter if the user is logged in or not it goes to the main page.
anf if i make the login page the home page everytime i restart the app it requires to login again.
i want it to be like once log in then be logged in till you log out
void main() async {
WidgetsFlutterBinding.ensureInitialized();
await Firebase.initializeApp();
runApp(MaterialApp(
debugShowCheckedModeBanner: false,
home: await getLandingPage(),
routes: {
'upload': (context) => ItemInput(),
'suzuki': (context) => Suzuki(),
'others': (context) => Others(),
},
));
}
Future<Widget> getLandingPage() async {
final FirebaseAuth _auth = FirebaseAuth.instance;
return StreamBuilder<User>(
stream: _auth.authStateChanges(),
builder: (BuildContext context, snapshot) {
if (snapshot.hasData && (!snapshot.data.isAnonymous)) {
return MainPage();
}
return LoginPage();
},
);
}

Answer 1

When the app is started, Firebase automatically restores the user's authentication state. This may take a few moments, as it needs to check with the server whether the account is still active.
During this time, the user will not be signed in yet, so authStateChanges() fires a null. And that's when your code redirects the user to the login page.
You'll want to either wait for a few moments to see if the user state is restored, or move/copy your navigation logic to the login page, so that it redirects to the main page once the user authentication state is restored.

Answer 2

Following on from Frank's answer, this is how to work around the issue of receiving a null on the first authStateChanges() event using a StreamBuilder widget.
#override
Widget build(BuildContext context) {
return StreamBuilder<User>(
stream: FirebaseAuth.instance.authStateChanges(),
builder: (BuildContext context, AsyncSnapshot<User> snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.waiting:
return _buildWaitingScreen();
default:
if (snapshot.hasError) {
return Text('Error: ${snapshot.error}');
} else {
final firebaseUser = snapshot.data;
if (firebaseUser != null) {
//....
}
return SignInPage();
}
}
});
}
If you don't want to use a switch statement, you can check only ConnectionState.active
#override
Widget build(BuildContext context) {
return StreamBuilder<User>(
stream: FirebaseAuth.instance.authStateChanges(),
builder: (BuildContext context, AsyncSnapshot<User> snapshot) {
if (snapshot.connectionState == ConnectionState.active) {
//...
}
return _buildWaitingScreen();
});
}

Answer 3

According to the docs:
A stream A source of asynchronous data events.
A Stream provides a way to receive a sequence of events. Each event is either a data event, also called an element of the stream, or an error event, which is a notification that something has failed. When a stream has emitted all its event, a single "done" event will notify the listener that the end has been reached.
Since the authStateChanges() returns a Stream then you can use the StreamBuilder to get the result and display the widgets accordingly.
According to the StreamBuilder docs:
As an example, when interacting with a stream producing the integers 0 through 9, the builder may be called with any ordered sub-sequence of the following snapshots that includes the last one (the one with ConnectionState.done):
new AsyncSnapshot.withData(ConnectionState.waiting, null)
new AsyncSnapshot.withData(ConnectionState.active, 0)
new AsyncSnapshot.withData(ConnectionState.active, 1)
...
new AsyncSnapshot.withData(ConnectionState.active, 9)
new AsyncSnapshot.withData(ConnectionState.done, 9)
Therefore the builder of type AsyncWidgetBuilder which is used for asynchronous operation, will call your widgets according to the state of the Stream, for example:
#override
Widget build(BuildContext context) {
final FirebaseAuth _auth = FirebaseAuth.instance;
return new Scaffold(
body: StreamBuilder(
stream: _auth.authStateChanges(),
builder: (context, AsyncSnapshot<FirebaseUser> snapshot) {
if (snapshot.connectionState == ConnectionState.active) {
if (snapshot.hasData)
return MainPage();
else
return LoginPage();
} else
return Center(
child: CircularProgressIndicator(),
);
}));
}
You can use the above code in the splash screen, here the Stream will be in the waiting state where it will display a loading first, and then when it retrieves the data, if it is either null or if there is a user logged in, it will enter the active state and return a widget which satisfies the condition.
https://api.flutter.dev/flutter/widgets/AsyncWidgetBuilder.html
https://api.flutter.dev/flutter/widgets/StreamBuilder-class.html
https://api.flutter.dev/flutter/widgets/StreamBuilder/builder.html
After talking with OP. They are using the following plugin google_sign_in, and have an auth.dart file with the following code:
void signOutGoogle() async {
await googleSignIn.signOut();
}
What happened in that case, is that the user signed out from Google auth but was still logged in inside Firebase, so to solve this you can add:
void signOutGoogle() async {
await googleSignIn.signOut();
await _auth.signOut();
}