Step14 StreamProvider

Goal of this step

  • Add StreamProvider

Ref:

Replace ChangeNotifierProvider with StreamProvider

lib/main.dart
MultiProvider(
providers: [
Provider<String>(create: (context) => testProviderText),
StreamProvider<FirebaseUser>(create: (context) => FirebaseAuth.instance.onAuthStateChanged)
],

Check the FirebaseAuth code

You see onAuthStateChanged returns stream.

firebase_auth-0.15.4/lib/src/firebase_auth.dart
/// Receive [FirebaseUser] each time the user signIn or signOut
Stream<FirebaseUser> get onAuthStateChanged {
return FirebaseAuthPlatform.instance.onAuthStateChanged(app.name).map(
(PlatformUser user) => user == null ? null : FirebaseUser._(user, app));
}

Delete code

lib/main.dart
bool isAuthenticated = false;
// https://stackoverflow.com/questions/41479255/life-cycle-in-flutter
// https://flutterbyexample.com/stateful-widget-lifecycle/
void initState() {
super.initState();
// https://firebase.google.com/docs/auth/web/manage-users
// https://stackoverflow.com/questions/45353730/firebase-login-with-flutter-using-onauthstatechanged
FirebaseAuth.instance.onAuthStateChanged.listen((user) {
// This is called when "sign-in" and "sign-out" is triggerd
print('onAuthStateChanged called!!!');
// If user signed-in already "user" is not null
setState(() {
isAuthenticated = user != null;
});
});
}

Fix existing code

Check login state by checking if login user exists.

lib/pages/home_page.dart and lib/widgets/home_drawer.dart

// final bool isAuthenticated = Provider.of<GlobalState>(context).isAuthenticated;
final user = Provider.of<FirebaseUser>(context);
final bool isAuthenticated = user != null;

Remove ChnageNotifier code

lib/pages/loin_page.dart, lib/pages/register_page.dart and lib/widgets/home_drawer.dart

Provider.of<GlobalState>(context, listen: false).updateIsAuthenticated(true or false);

Test it!

Everything works like a charm!!

Recap StreamProvider

StreamProvider<FirebaseUser>(create: (context) => FirebaseAuth.instance.onAuthStateChanged)

In this code,

FirebaseAuth.instance.onAuthStateChanged

is called when user "sign-in" or "sign-out" and return <FirebaseUser>.

And StremProvider automatically provide new value.

That's why you don't need to call

Provider.of<GlobalState>(context, listen: false).updateIsAuthenticated(true or false);

If you want to dive into Stream

Stream is comming from Reactive Programming.

I've got used to using it but I don't 100% understand it!

If you want to dive into Stream check the below links!

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