I have a class called FeedbackEdit that requires data in a variable called feedback to run correctly. I must get feedback from a backend API call. Currently, the code I have runs, but it shows an error for one second while it is retrieving data from the back-end. What would be the best way to fix this so it runs continuously?
class FeedbackEdit extends StatefulWidget {
#override
_FeedbackEditState createState() => _FeedbackEditState();
}
class _FeedbackEditState extends State<FeedbackEdit> {
MyFeedback feedback;
void initState() {
super.initState();
asyncGetFeedback();
}
void asyncGetFeedback() async {
MyFeedback data = await fetchFeedback(http.Client());
setState(() {
feedback = data;
});
}
Widget build(BuildContext context) { ...
it's because you are rendering your view while still fetching data from the backend. To solve the issue, you should use FutureBuilder (see) in your build method. That will make your view to wait the response being fetched from backend.
A sample code I wrote in one of my projects:
FutureBuilder<List<SingleQuestion>>(
future: retrieveFavedQuestions(questionIds),
builder: (context, favQuestionssnapshot) {
if (favQuestionssnapshot.connectionState ==
ConnectionState.done) {
if (favQuestionssnapshot.hasError) {
// check error
}
if (favQuestionssnapshot.hasData) {
// continue working with your data
}
}
);
Related
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!))),
),
);
}
}
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.
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())) :
Updates:
2021/06/11 After hours of debugging yesterday, I confirmed that the problem is caused by aws amplify configuration: _configureAmplify(). Because the location of the amplify server was set wrong, so _configureAmplify() takes several seconds to work... and therefore, the readPost() function did not work on initialization, as it must run after _configureAmplify()...
2021/06/10I made changes to my code according to S. M. JAHANGIR's advice, and updated the question. The issue still presists. The value of posts is not updated when called in initialization and the data only shows up after reload. (if I commented out the _controller.readPost() in UI, the value of posts is always empty.
I have this page that loads information from aws amplify with getx implemented. However, I found out the readPost() async funtion in getx controller dart file is not reading from database, when the controller instance is initialized. I have to add a _controller.readPost() in UI file to make it work. And the data only shows up after a reload of that UI page...
Getx Controller dart file:
class ReadPostController extends GetxController {
var isLoading = true.obs;
var posts = <Posty>[].obs;
#override
void onInit() {
_configureAmplify();
await readPost();
super.onInit();
// print('show post return value: $posts');
}
void _configureAmplify() {
final provider = ModelProvider();
final dataStorePlugin = AmplifyDataStore(modelProvider: provider);
AmplifyStorageS3 storage = new AmplifyStorageS3();
AmplifyAuthCognito auth = new AmplifyAuthCognito();
AmplifyAPI apiRest = AmplifyAPI();
// Amplify.addPlugin(dataStorePlugin);
Amplify..addPlugins([dataStorePlugin, storage, auth, apiRest]);
Amplify.configure(amplifyconfig);
print('Amplify configured');
}
// read all posts from databases
Future readPost() async {
try {
isLoading(true);
var result = await Amplify.DataStore.query(Posty.classType);
print('finish loading request');
result = result.sublist(1);
posts.assignAll(result);
// print(the value of posts is $posts');
} finally {
isLoading(false);
}
}
#override
void onClose() {
// called just before the Controller is deleted from memory
super.onClose();
}
}
And in the UI part:
class TabBody extends StatelessWidget {
TabBody({Key? key}) : super(key: key);
final ReadPostController _controller = Get.put(ReadPostController());
#override
Widget build(BuildContext context) {
_controller.readPost();//if commented out, _controller.post is empty
return Container(
child: Obx(
() => Text('showing：${_controller.posts[1].title}'),
));
}
}
In my understanding, the readPost() function should be called when the ReadPost_controller is initiallized. And the UI will update when the posts = <Posty>[].obs changes. Guys, what am I doing wrong here?
First, when you are calling readPost on onInit you are not awaiting. So change it to:
onInit() async{
...
await readPost();
...
}
Secondly, posts is a RxList so you need to use the assignAll method to update it.
Therefore, in your readPost method, instead of posts.value = reault you need to use posts.assignAll(result)
Calling from the UI works because readPost every time the build method is called by the Flutter framework and actually the UI shows the data from every previous call.
I think try with GetBuilder instead of Obx.
GetBuilder<ReadPostController>(
builder: (value) => Text('showing：${value.posts[1].title}'),
)
and also use update(). in readPost() method.
my UI consists of a table of objects Apples.
Every cell in the table:
has an ADD button, if the apple is NOT present for that cell
it shows the apple and has a DELETE button, if the apple is present
The main page of my application is calling the following widget to LOAD the LIST of apples from an API. And also the ADD and DELETE functions communicate with the same API for adding and deleting the apple.
class ApplesLoader extends StatefulWidget {
#override
_ApplesLoaderState createState() => _ApplesLoaderState();
}
class _ApplesLoaderState extends State<ApplesLoader> {
#override
void initState() {
super.initState();
BlocProvider.of<ApplesCubit>(context).getAll();
}
#override
Widget build(BuildContext context) {
return BlocConsumer<ApplesCubit, ApplesState>(
listener: ...,
builder: (ctx, state) {
if (!(state is ApplesLoaded)) {
return circularProgressIndicator;
}
return ApplesViewer(state.Apples);
},
);
}
}
So after that ApplesViewerhas the list of apples and can correctly display the grid.
But now I have two problems:
When I press the ADD button or the DELETE button, all the application is rebuilt, while I could actually just re-paint the cell. But I don't know how to avoid this, because I also need to communicate to the application that the list of apples is actually changed. I don't want to rebuild the entire UI because it seems inefficient since what is actually changing on my page is only the selected cell.
When I press the ADD button or the DELETE button, I would like to show a circular progress indicator that replaces the button (while waiting for the API to actually creating/deleting the apple). But when the list changes, all the application is rebuilt instead. So, I am not sure how to achieve this desired behavior.
Could you help me in solving those two issues?
Or advise me for a change of infrastructure in case I am making some mistake in dealing with this?
If needed, this is the code for ApplesCubit
class ApplesCubit extends Cubit<ApplesState> {
final ApplesRepository _repository;
ApplesCubit(this._repository) : super(ApplesLoading());
Future<void> getAll() async {
try {
final apples = await _repository.getAll();
emit(ApplesLoaded(List<Apple>.from(apples)));
} on DataError catch (e) {
emit(ApplesError(e));
}
}
Future<void> create(List<Apple> apples, Apple appleToAdd) async {
try {
final newApple = await _repository.create(appleToAdd);
final updatedApples = List<Apple>.from(apples)..add(newApple);
emit(ApplesLoaded(updatedApples));
} on DataError catch (e) {
emit(ApplesError(e));
}
}
Future<void> delete(List<Apple> Appless, Apple appleToDelete) async {
try {
await _repository.deleteApples(appleToDelete);
final updatedApples = List<Apple>.from(Appless)..remove(appleToDelete);
emit(ApplesLoaded(updatedApples));
} on DataError catch (e) {
emit(ApplesError(e));
}
}
}
I'm programming a flutter application in which a user is presented with a PageView widget that allows him/her to navigate between 3 "pages" by swiping.
I'm following the setup used in https://medium.com/flutter-community/flutter-app-architecture-101-vanilla-scoped-model-bloc-7eff7b2baf7e, where I use a single class to load data into my model, which should reflect the corresponding state change (IsLoadingData/HasData).
I have a main page that holds all ViewPage widgets. The pages are constructed in the MainPageState object like this:
#override
void initState() {
_setBloc = SetBloc(widget._repository);
_notificationBloc = NotificationBloc(widget._repository);
leftWidget = NotificationPage(_notificationBloc);
middleWidget = SetPage(_setBloc);
currentPage = middleWidget;
super.initState();
}
If we go into the NotificationPage, then the first thing it does is attempt to load data:
NotificationPage(this._notificationBloc) {
_notificationBloc.loadNotificationData();
}
which should be reflected in the build function when a user directs the application to it:
//TODO: Consider if state management is correct
#override
Widget build(BuildContext context) {
return StreamBuilder<NotificationState>(
stream: _notificationBloc.notification.asBroadcastStream(),
//initialData might be problematic
initialData: NotificationLoadingState(),
builder: (context, snapshot) {
if (snapshot.data is NotificationLoadingState) {
return _buildLoading();
}
if (snapshot.data is NotificationDataState) {
NotificationDataState state = snapshot.data;
return buildBody(context, state.notification);
} else {
return Container();
}
},
);
}
What happens is that the screen will always hit "NotificationLoadingState" even when data has been loaded, which happens in the repository:
void loadNotificationData() {
_setStreamController.sink.add(NotificationState._notificationLoading());
_repository.getNotificationTime().then((notification) {
_setStreamController.sink
.add(NotificationState._notificationData(notification));
print(notification);
});
}
The notification is printed whilst on another page that is not the notification page.
What am i doing wrong?
//....
class _SomeState extends State<SomeWidget> {
//....
Stream<int> notificationStream;
//....
#override
void initState() {
//....
notificationStream = _notificationBloc.notification.asBroadcastStream()
super.initState();
}
//....
Widget build(BuildContext context) {
return StreamBuilder<NotificationState>(
stream: notificationStream,
//....
Save your Stream somewhere and stop initialising it every time.
I suspect that the build method is called multiple times and therefore you create a new stream (initState is called once).
Please try let me know if this helped.
I have 3 classes: Users, Posts and Comments. User has many Posts and
Posts has many Comments.
I want that all data to be fetched before the widget's build method is called.
I tryed to use initState() to do this:
class FetchDataExample extends StatefulWidget {
final User _user;
FetchDataExample(this._user);
#override
_State createState() => _State(_user);
}
class _State extends State<FetchDataExample> {
final User _user;
_State(this._user);
#override
void initState() {
_user.setPosts();
super.initState();
}
#override
Widget build(BuildContext context) {
print(this._user.posts[0]);
return Container(
);
}
}
In User class I have:
void setPosts() async {
String url = 'https://jsonplaceholder.typicode.com/posts?userId=' + this.id.toString();
var request = Requester.get(url); // Returns a Future<Response>
await request.then((value) => this.posts = Post.jsonToPosts(json.decode(value.body)));
this.posts.forEach((post) => post.setComments());
print(this.posts[0]);
}
The 'setComments()' has the same logic.
I have two prints:
Inside build that returns null;
Inside setPosts the returns Instance of 'Post';
So, by the time that Build method is called in the widget, the initState has not finished yet.
I need it be finished, does anyone know how can I do that?
You can use a FutureBuilder to build a widget by using latest result from a future.
And also you can combile multiple futures into a single one using Future.wait method.
Here is a sample code:
_getPageData() async {
var _combinedFutures = await Future.wait([setPosts, setComments]);
//do stuff with data
}
...
#override
Widget build(BuildContext context) {
return FutureBuilder(
future:_getPageData(),
builder: (context, snapshot) {
return Container();
}),
);
});