Flutter Provider: Provide 2 streams with one dependent on the other

Question

I'm using the provider package. In the root of the widget tree I have a multiprovider:

Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        StreamProvider<FirebaseUser>.value(
            value: FirebaseConnection.getAuthenticationStream()),
        StreamProvider<User>.value(
            value: FirebaseConnection.getUserStream(uid: ???))
      ],
      child: MaterialApp(
        debugShowCheckedModeBanner: false,
        initialRoute: LoginScreen.id,
        onGenerateRoute: RouteGenerator.generateRoute,
      ),
    );
  }

The first StreamProvider provides the logged in user from firebase_auth. The second StreamProvider is supposed to provide additional information to that user (stored in the users collection). The problem is that to get the second stream I need the uid of the FirebaseUser provided with the first stream but I don't know how to access it.

Nesting the StreamProviders didn't work because in the second stream I can only access the (wrong) context of the build method (for Provider.of(context))

Solution

The solution is to save the second stream (loggedInUserStream) in the state and change it whenever the first stream (authenticationStream) emits a new value (by listening to it) like in the code below:

class _FloatState extends State<Float> {
  StreamSubscription<FirebaseUser> authenticationStreamSubscription;
  Stream<User> loggedInUserStream;

  StreamSubscription<FirebaseUser> setLoggedInUserStream() {
    authenticationStreamSubscription =
        FirebaseConnection.getAuthenticationStream().listen((firebaseUser) {
      loggedInUserStream =
          FirebaseConnection.getUserStream(uid: firebaseUser?.uid);
    });
  }

  @override
  void initState() {
    super.initState();
    authenticationStreamSubscription = setLoggedInUserStream();
  }

  @override
  void dispose() {
    super.dispose();
    authenticationStreamSubscription.cancel();
  }

  @override
  Widget build(BuildContext context) {
    return StreamProvider<User>.value(
      value: loggedInUserStream,
      child: MaterialApp(
        debugShowCheckedModeBanner: false,
        initialRoute: LoginScreen.id,
        onGenerateRoute: RouteGenerator.generateRoute,
      ),
    );
  }
}

I only needed the first stream (authenticationStream) to get the second one (loggedInUserStream) so I didn't provide it to the widgets below.