Flutter GetX state management initial null value - flutter

Question

This is what I'm trying to achieve using flutter GetX package but not working properly.
I have a Firestore document, if the document is changed I want to call an api and keep the data up to date as observable.
The code below seems to work but initial screen shows null error then it shows the data.
I don't know how I can make sure both fetchFirestoreUser() and fetchApiData() (async methods) returns data before I move to the home screen.
GetX StateMixin seems to help with async data load problem but then I don't know how I can refresh the api data when the firestore document is changed.
I'm not sure if any other state management would be best for my scenario but I find GetX easy compared to other state management package.
I would very much appreciate if someone would tell me how I can solve this problem, many thanks in advance.
Auth Controller.
class AuthController extends SuperController {
static AuthController instance = Get.find();
late Rx<User?> _user;
FirebaseAuth auth = FirebaseAuth.instance;
var _firestoreUser = FirestoreUser().obs;
var _apiData = ProfileUser().obs;
#override
void onReady() async {
super.onReady();
_user = Rx<User?>(auth.currentUser);
_user.bindStream(auth.userChanges());
//get firestore document
fetchFirestoreUser();
//fetch data from api
fetchApiData();
ever(_user, _initialScreen);
//Refresh api data if firestore document has changed.
_firestoreUser.listen((val) {
fetchApiData();
});
}
Rx<FirestoreUser?> get firestoreUser => _firestoreUser;
_initialScreen(User? user) {
if (user == null) {
Get.offAll(() => Login());
} else {
Get.offAll(() => Home());
}
}
ProfileUser get apiData => _apiData.value;
void fetchFirestoreUser() async {
Stream<FirestoreUser> firestoreUser =
FirestoreDB().getFirestoreUser(_user.value!.uid);
_firestoreUser.bindStream(firestoreUser);
}
fetchApiData() async {
var result = await RemoteService.getProfile(_user.value!.uid);
if (result != null) {
_apiData.value = result;
}
}
#override
void onDetached() {}
#override
void onInactive() {}
#override
void onPaused() {}
#override
void onResumed() {
fetchApiData();
}
}
Home screen
class Home extends StatelessWidget {
const Home({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: Container(
child: Obx(() =>
Text("username: " + AuthController.instance.apiData.username!))),
),
);
}
}

Answer 1

To be honest, I never used GetX so I'm not too familiar with that syntax.
But I can see from your code that you're setting some mutable state when you call this method:
fetchApiData() async {
var result = await RemoteService.getProfile(_user.value!.uid);
if (result != null) {
_apiData.value = result;
}
}
Instead, a more robust solution would be to make everything reactive and immutable. You could do this by combining providers if you use Riverpod:
final authStateChangesProvider = StreamProvider.autoDispose<User?>((ref) {
final authService = ref.watch(authRepositoryProvider);
return authService.authStateChanges();
});
final apiDataProvider = FutureProvider.autoDispose<APIData?>((ref) {
final userValue = ref.watch(authStateChangesProvider);
final user = userValue.value;
if (user != null) {
// note: this should also be turned into a provider, rather than using a static method
return RemoteService.getProfile(user.uid);
} else {
// decide if it makes sense to return null or throw and exception when the user is not signed in
return Future.value(null);
}
});
Then, you can just use a ConsumerWidget to watch the data:
#override
Widget build(BuildContext context, WidgetRef ref) {
// this will cause the widget to rebuild whenever the auth state changes
final apiData = ref.watch(apiDataProvider);
return apiData.when(
data: (data) => /* some widget */,
loading: () => /* some loading widget */,
error: (e, st) => /* some error widget */,
);
}
Note: Riverpod has a bit of a learning curve (worth it imho) so you'll have to learn it how to use it first, before you can understand how this code works.

Answer 2

Actually the reason behind this that you put your controller in the same page that you are calling so in the starting stage of your page Get.put() calls your controller and because you are fetching data from the API it takes a few seconds/milliseconds to get the data and for that time your Obx() renders the error. To prevent this you can apply some conditional logic to your code like below :
Obx(() => AuthController.instance.apiData != null ? Text("username: " + AuthController.instance.apiData.username!) : CircularProgressIndicator())) :