I am creating a subscription with GraphQL, and I need to consume that subscription with Flutter, but I don't know how to do that, the thing that I need is something like a UI component that would be tied to a subscription and it will be automatically refreshed.
I will appreciate any feedback.
My GraphqlServer runs a subscription named getLogs which returns the log information in the following format.
{
"data": {
"getLogs": {
"timeStamp": "18:09:24",
"logLevel": "DEBUG",
"file": "logger.py",
"function": "init",
"line": "1",
"message": "Hello from logger.py"
}
}
}
If you are like me who wants to use only the GraphQL Client directly, then following sample could help.
import 'package:graphql/client.dart';
import 'package:graphql/internal.dart';
import 'package:flutter/material.dart';
import 'dart:async';
class LogPuller extends StatefulWidget {
static final WebSocketLink _webSocketLink = WebSocketLink(
url: 'ws://localhost:8000/graphql/',
config: SocketClientConfig(
autoReconnect: true,
),
);
static final Link _link = _webSocketLink;
#override
_LogPullerState createState() => _LogPullerState();
}
class _LogPullerState extends State<LogPuller> {
final GraphQLClient _client = GraphQLClient(
link: LogPuller._link,
cache: InMemoryCache(),
);
// the subscription query should be of the following format. Note how the 'GetMyLogs' is used as the operation name below.
final String subscribeQuery = '''
subscription GetMyLogs{
getLogs{
timeStamp
logLevel
file
function
line
message
}
}
''';
Operation operation;
Stream<FetchResult> _logStream;
#override
void initState() {
super.initState();
// note operation name is important. If not provided the stream subscription fails after first pull.
operation = Operation(document: subscribeQuery, operationName: 'GetMyLogs');
_logStream = _client.subscribe(operation);
}
#override
Widget build(BuildContext context) {
return StreamBuilder(
stream: _logStream,
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return Center(
child: Container(
child: CircularProgressIndicator(
strokeWidth: 1.0,
),
),
);
}
if (snapshot.hasData) {
return Center(
child: Text(
snapshot.data.data['getLogs']
['message'], // This will change according to you needs.
),
);
}
return Container();
},
);
}
}
As I am using a StreamBuilder to build the widget it will take care of closing the stream. If this is not the case for you, stream.listen() method will return a StreamSubscription<FetchResult> object which you can call the cancel() method which can be done inside dispose() method of a stateful widget or any such method for a standalone Dart client.
You can check the next library https://github.com/zino-app/graphql-flutter
Just find out the bug in this library, Just open the subscription.dart file by ctrl+click on Subscription. In that file, it is easy to see that socketClient variable is null. So just define it in initState() function as shown in the docs. Restart your app. And it works like a charm. So, basically, you just need to initialize that variable in the subscription.dart file.
Related
I'm rebuilding an iOS app using Flutter and the flow is as followed:
Everytime the user lands on the homepage, the user data is reloaded from the backend to check if anything has changed.
The way I achieve this in Swift / iOS is by using the viewDidLoad() function.
My Flutter code is like this:
class HomePage extends StatefulWidget {
#override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
User user = User();
#override
void dispose() {
super.dispose();
}
#override
void initState() {
super.initState();
_fetchData(context);
}
#override
Widget build(BuildContext context) {
return Container(
color: RColor.COLOR_main,
child: Column(
children: [
Container(
height: MediaQuery.of(context).size.height / 7,
width: MediaQuery.of(context).size.width,
padding: EdgeInsets.all(20),
child: Container(
child: Text("This is the homepage"),
alignment: Alignment.bottomCenter,
),
),
],
));
}
Future _fetchData(BuildContext context) async {
_fetchUserAPI(context);
}
Future _fetchUserAPI(BuildContext context) async {
try {
SharedPreferences prefs = await SharedPreferences.getInstance();
var accessToken = prefs.getString("access_token");
var url = RConstants.API_BASE_URL + "/v1/users/self";
Response response = await Dio()
.get(url, options: Options(headers: {"Authorization": accessToken}));
setState(() {
user = User.fromJson(response.data);
});
} catch (e) {
print(e.toString());
Alert(
context: context,
title: "Something Went Wrong",
desc: "Something went wrong while fetching your user data",
type: AlertType.error)
.show();
}
}
}
void initState() however, doesn't get triggered each time the user lands on the homepage. What is the correct way to achieve this?
Well, it really depends on what exactly you mean by "Everytime the user lands on the homepage".
If user navigates from the HomePage to some other view via Navigator.push and then goes back via Navigator.pop then the HomePage's state remain the same and of course the initState method does not trigger.
If you want to get notified on the HomePage if the route above it in the navigator gets popped then you need to use this method, override it and then inside it you will be able to call the _fetchData() and update the homepage's state.
One more thing: when you have some async call like _fetchData() it is a wrong pattern to just invoke it inside the initState() or any other framework methods. Because it will be invoked and the build() method of your state will almost always be invoked immediately before the result of async call will come back. The correct way to handle such situations is to use the FutureBuilder widget.
If "Everytime the user lands on the homepage" means something else, like e.g. the app was in the background and gets brought foreground or when there is support for push notifications implemented and users click on the notification and the app is opened - such cases also can be handled but that is a broader topic.
RouteAware can help.
define final RouteObserver<ModalRoute<void>> routeObserver = RouteObserver<ModalRoute<void>>(); in main.dart.
set navigatorObservers: [ routeObserver ], in MaterialApp function.
mixin RouteAware in your page that need achieve viewWillAppear feature.
override didChangeDependencies and didPopNext methods and subscribe this page to routeObserver.
For example:
main.dart
final RouteObserver<ModalRoute<void>> routeObserver = RouteObserver<ModalRoute<void>>();
void main() {
runApp(MaterialApp(
home: HomePage(),
navigatorObservers: [ routeObserver ],
));
}
home_page.dart
class _HomePageState extends State<HomePage> with RouteAware {
#override
void didChangeDependencies() {
super.didChangeDependencies();
routeObserver.subscribe(this, ModalRoute.of(context)!);
}
#override
void dispose() {
routeObserver.unsubscribe(this);
super.dispose();
}
#override
void didPopNext() {
super.didPopNext();
debugPrint("viewWillAppear");
}
}
these my two classes(two pages). these two classes open multiple times.
I put debug point in futurebuilder in two classes.
debug point running,
MainCategory page and got to the next page
SubCategory page and again running MainCategory page(previous page) futurebuilder and again running MainCategory page futurebuilder
navigate subcategory page to third page running subcategory page and main category page
I upload my two classes to GitHub and please let me know what the issue is.
MainCategory code: https://github.com/bhanuka96/ios_login/blob/master/MainCategory.dart
SubCategory code: https://github.com/bhanuka96/ios_login/blob/master/subCategory.dart
As stated in the documentation, you should not fetch the Future for the Futurebuilder during the widget's build event.
https://docs.flutter.io/flutter/widgets/FutureBuilder-class.html
The future must have been obtained earlier, e.g. during
State.initState, State.didUpdateConfig, or
State.didChangeDependencies. It must not be created during the
State.build or StatelessWidget.build method call when constructing the
FutureBuilder. If the future is created at the same time as the
FutureBuilder, then every time the FutureBuilder's parent is rebuilt,
the asynchronous task will be restarted.
So, try to move your call to getRegister method outside the build method and replace it with the returned Future value.
For example, below I have a class that returns a Future value which will be consumed with the help of FutureBuilder.
class MyApiHelper{
static Future<List<String>> getMyList() async {
// your implementation to make server calls
return List<String>();
}
}
Now, inside your widget, you will have something like this:
class _MyHomePageState extends State<MyHomePage> {
Future<List<String>> _myList;
#override
void initState() {
super.initState();
_myList = MyApiHelper.getMyList();
}
#override
Widget build(BuildContext context) {
return Scaffold(body: FutureBuilder(
future: _myList,
builder: (_, AsyncSnapshot<List<String>> snapLs) {
if(!snapLs.hasData) return CircularProgressIndicator();
return ListView.builder(
itemCount: snapLs.data.length,
itemBuilder: (_, index) {
//show your list item row here...
},
);
},
));
}
}
As shown above, the Future is fetched in the initState function and used inside the build method and used by FutureBuilder.
I hope this was helpful.
Thanks.
If you happen to use Provider, here's (in my opinion) a clearer alternative based on your question:
class MyHomePage extends StatelessWidget {
#override
Widget build(BuildContext context) {
return FutureProvider<List<String>>(
create: (_) => MyApiHelper.getMyList(),
child: Consumer<List<String>>(
builder: (_, list, __) {
if (list == null) return CircularProgressIndicator();
return ListView.builder(
itemCount: list.length,
itemBuilder: (_, index) {
//show your list item row here...
},
);
};
),
);
}
}
This can also be achieved of course as a StatefulWidget as suggested by the other answer, or even with flutter_hooks as explained in Why is my Future/Async Called Multiple Times?
You can create new Widget and pass Function to
returnFuture as
() {
return YourFuture;
}
import 'dart:developer';
import 'package:flutter/material.dart';
class MyFutureBuilder<T> extends StatefulWidget {
final Future<T> Function() returnFuture;
final AsyncWidgetBuilder<T> builder;
final T initialData;
MyFutureBuilder({
this.returnFuture,
#required this.builder,
this.initialData,
Key key,
}) : super(key: key);
#override
_MyFutureBuilderState<T> createState() => _MyFutureBuilderState<T>();
}
class _MyFutureBuilderState<T> extends State<MyFutureBuilder<T>> {
bool isLoading = false;
Future<T> future;
#override
void initState() {
super.initState();
future = widget.returnFuture();
}
#override
Widget build(BuildContext context) {
return FutureBuilder(
builder: widget.builder,
initialData: widget.initialData,
future: future,
);
}
}
Example
MyFutureBuilder<List<User>>(
returnFuture: () {
return moderatorUserProvider
.getExecutorsAsModeratorByIds(val.users,
save: true);
},
builder: (cont, asyncData) {
if (asyncData.connectionState !=
ConnectionState.done) {
return Center(
child: MyCircularProgressIndicator(
color: ModeratorColor.executors.color,
),
);
}
return Column(
children: asyncData.data
.map(
(singlExecutor) =>
ChooseInfoButton(
title:
'${singlExecutor.firstName} ${singlExecutor.secondName}',
subTitle: 'Business analyst',
middleText: '4.000 NOK',
subMiddleText: 'full time',
label: 'test period',
subLabel: '1.5 month',
imageUrl:
assetsUrl + 'download.jpeg',
onTap: () {
Navigator.of(context).push(
MaterialPageRoute(
builder: (_) =>
ModeratorExecutorEditPage(),
),
);
},
),
)
.toList());
},
)
```
I am struggling with RxDart (maybe just straight up Rx programming). I currently have a stateful widget that calls my bloc in it's didChangeDependencies(). That call goes out and gets data via http request and adds it to a stream. I'm using BehaviorSubject and this works fine. I have child widgets using StreamBuilders and they get data no problem. My issue comes in dealing with errors. If my http request fails, I hydrate the stream with addError('whatever error') but my child widget's StreamBuilder is not receiving that error. It doesn't get anything at all.
So I have a few questions.
Is that expected?
Should error handling not be done in StreamBuilder? Ideally, I want to show something in the UI if something goes wrong so not sure how else to do it.
I could make my child widget stateful and use stream.listen. I do receive the errors there but it seems like overkill to have that and the StreamBuilder.
Am I missing something fundamental here about streams and error handling?
Here is my bloc:
final _plans = BehaviorSubject<List<PlanModel>>();
Observable<List<PlanModel>> get plans => _plans.stream;
fetchPlans() async {
try {
final _plans = await _planRepository.getPlans();
_plans.add(_plans);
}
on AuthenticationException {
_plans.addError('authentication error');
}
on SocketException {
_plans.addError('no network connection');
}
catch(error) {
_plans.addError('fetch unsuccessful');
}
}
Simplified Parent Widget:
class PlanPage extends StatefulWidget {
#override
PlanPageState createState() {
return new PlanPageState();
}
}
class PlanPageState extends State<PlanPage> {
#override
void didChangeDependencies() async {
super.didChangeDependencies();
var planBloc = BaseProvider.of<PlanBloc>(context);
planBloc.fetchPlans();
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar( title: const Text('Your Plan') ),
body: PlanWrapper()
);
}
}
Simplified Child Widget with StreamBuilder:
class PlanWrapper extends StatelessWidget {
#override
Widget build(BuildContext context) {
var planBloc = BaseProvider.of<PlanBloc>(context);
return StreamBuilder(
stream: planBloc.plans,
builder: (BuildContext context, AsyncSnapshot<List<PlanModel>> plans) {
if (plans.hasError) {
//ERROR NEVER COMES IN HERE
switch(plans.error) {
case 'authentication error':
return RyAuthErrorCard();
case 'no network connection':
return RyNetworkErrorCard();
default:
return RyGenericErrorCard(GeneralException().errorMessages()['message']);
}
}
if (plans.hasData && plans.data.isNotEmpty) {
return ListView(
physics: const AlwaysScrollableScrollPhysics(),
children: _buildPlanTiles(context, plans.data)
);
}
return Center(child: const CircularProgressIndicator());
}
);
}
}
There was an issue about this in the RxDart GitHub (https://github.com/ReactiveX/rxdart/issues/227). BehaviorSubjects were not replaying errors to new listeners.
It was fixed in version 0.21.0. "Breaking Change: BehaviorSubject will now emit an Error, if the last event was also an Error. Before, when an Error occurred before a listen, the subscriber would not be notified of that Error."
I am using sqflite database to save user list.
I have user list screen, which shows list of user and it has a fab button,
on click of fab button, user is redirected to next screen where he can add new user to database.
The new user is properly inserted to the database
but when user presses back button and go backs to user list screen,
the newly added user is not visible on the screen.
I have to close the app and reopen it,then the newly added user is visible on the screen.
I am using bloc pattern and following is my code to show user list
class _UserListState extends State<UserList> {
UserBloc userBloc;
#override
void initState() {
super.initState();
userBloc = BlocProvider.of<UserBloc>(context);
userBloc.fetchUser();
}
#override
void dispose() {
userBloc?.dispose();
super.dispose();
}
#override
Widget build(BuildContext context) {
return Scaffold(
floatingActionButton: FloatingActionButton(
onPressed: () {
Navigator.of(context).pushNamed("/detail");
},
child: Icon(Icons.add),
),
body: StreamBuilder(
stream: userBloc.users,
builder: (context, AsyncSnapshot<List<User>> snapshot) {
if (!snapshot.hasData) {
return Center(
child: CircularProgressIndicator(),
);
}
if (snapshot.data != null) {
return ListView.builder(
itemBuilder: (context, index) {
return Dismissible(
key: Key(snapshot.data[index].id.toString()),
direction: DismissDirection.endToStart,
onDismissed: (direction) {
userBloc.deleteParticularUser(snapshot.data[index]);
},
child: ListTile(
onTap: () {
Navigator.of(context).push(MaterialPageRoute(
builder: (context) => UserDetail(
user: snapshot.data[index],
)));
},
title: Text(snapshot.data[index].name),
subtitle:
Text("Mobile Number ${snapshot.data[index].userId}"),
trailing:
Text("User Id ${snapshot.data[index].mobileNumber}"),
),
);
},
itemCount: snapshot.data.length,
);
}
},
),
);
}
}
Following is my bloc code
class UserBloc implements BlocBase {
final _users = BehaviorSubject<List<User>>();
Observable<List<User>> get users => _users.stream;
fetchUser() async {
await userRepository.initializeDatabase();
final users = await userRepository.getUserList();
_users.sink.add(users);
}
insertUser(String name,int id,int phoneNumber) async {
userRepository.insertUser(User(id, name, phoneNumber));
fetchUser();
}
updateUser(User user) async {
userRepository.updateUser(user);
}
deleteParticularUser(User user) async {
userRepository.deleteParticularUser(user);
}
deleteAllUser() {
return userRepository.deleteAllUsers();
}
#override
void dispose() {
_users.close();
}
}
As Remi posted answer saying i should try BehaviorSubject and ReplaySubject which i tried but it does not help. I have also called fetchUser(); inside insertUser() as pointed in comments
Following is the link of the full example
https://github.com/pritsawa/sqflite_example
Follow up from the comments, it seems you don't have a single instance of your UsersBloc in those two pages. Both the HomePage and UserDetails return a BlocProvider which instantiate a UsersBloc instance. Because you have two blocs instances(which you shouldn't have) you don't update the streams properly.
The solution is to remove the BlocProvider from those two pages(HomePage and UserDetail) and wrap the MaterialApp widget in it to make the same instance available to both pages.
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return BlocProvider(
bloc: UserBloc(),
child:MaterialApp(...
The HomePage will be:
class HomePage extends StatelessWidget {
#override
Widget build(BuildContext context) {
return UserList(),
);
}
}
Remove the BlocProvider from UserDetail as well.
In the UsersBloc then call fetchUser() inside the insertUser() method after the user insertion, to requery the database and update the users stream.
Also as Rémi Rousselet said, use one of the subjects that return previous values.
The issue is that you're using a PublishSubject.
When a new listener subscribes to a PublishSubject, it does not receive the previously sent value and will only receive the next events.
The easiest solution is to use a BehaviorSubject or a ReplaySubject instead. These two will directly call their listener with the latest values.
#override
void initState() {
super.initState();
userBloc = BlocProvider.of<UserBloc>(context);
userBloc.fetchUser();
}
The problem is that you have called the userBloc.fetchUser() function in the initState of the page.
Bloc stream emits whenever a new data is added to it and the userBloc.fetchUser() function does exactly that, it adds the userList that you fetch from the Sqflite database.
Whenever you come back to the userlist screen from add user screen, init function is NOT called. It is only called when the userlist screen is created, that is, whenever you push it to the navigation stack.
The workaround is to call userBloc.fetchUser() whenever your StreamBuilder's snapshot data is null.
...
if (!snapshot.hasData) {
userBloc.fetchUser();
return Center(
child: CircularProgressIndicator(),
);
}
...
I currently have a simple API but my flutter widgets could not detect the changes happening in the API without restarting the whole application.
The API was made as a test API on https://www.mockable.io/. I managed to read from this API using a StreamBuilder. And still it does not change the values in the widget whenever i update their value in the API.
Default JSON
{
"id": "123",
"token": "1token",
"status": "Valid"
}
After Value Change
{
"id": "123",
"token": "1token",
"status": "Not Valid"
}
My StreamBuilder Code
import 'package:flutter/material.dart';
import 'dart:async';
import 'dart:convert';
import 'package:http/http.dart' as http;
final String url = "http://demo2722084.mockable.io/user";
class StreamPage extends StatefulWidget {
#override
StreamPageState createState() {
return new StreamPageState();
}
}
class StreamPageState extends State<StreamPage> {
StreamController _userController;
Future fetchUser() async{
final response = await http.get(url);
if(response.statusCode == 200){
return json.decode(response.body);
}else{
print("Exception caught: Failed to get data");
}
}
loadUser() async{
fetchUser().then((res) async{
_userController.add(res);
return res;
});
}
#override
void initState() {
_userController = new StreamController();
loadUser();
super.initState();
}
#override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text("Stream"),
),
body: new StreamBuilder(
stream: _userController.stream,
builder: (context, snapshot){
if(snapshot.hasError){
print("Exception: ${snapshot.error}");
}
if(snapshot.hasData){
var user = snapshot.data;
var id = user["id"] ?? "";
var token = user["token"] ?? "";
var status = user["status"] ?? "";
return new Center(
child: new ListTile(
title: new Text("Token: $token"),
subtitle: new Text("Status: $status"),
leading: new Text(id),
),
);
}
if(snapshot.connectionState != ConnectionState.waiting){
return new Center(
child: new CircularProgressIndicator(),
);
}
if(!snapshot.hasData && snapshot.connectionState != ConnectionState.done){
return new Center(
child: new CircularProgressIndicator(),
);
}
},
),
);
}
}
I expected the StreamBuilder to pick up the changed status value but the app has to be restarted for the new value to be reflected in the app.
Is there an example of how I can achieve this properly since this is quite frankly my first time trying out a StreamBuilder.
Your HTTP request results in just one data point, so for that you could use a FutureBuilder. But you want to know when something changes at the server. Your HTTP connection has finished when the change is made and so has no idea that it has happened.
There are several ways to detect changes at the server, for example, polling, user-initiated refresh, websockets, etc. For demonstration purposes, instead of calling loadUser in initState you could start a 1 second periodic timer to do that, which would update the stream every second and you should see the change. (Don't forget to cancel the timer in dispose.)
That's unlikely to be viable in production, so explore websockets, etc for pushed notifications from the web server. Also explore whether Firebase Cloud Messaging is a better way to send notification of changes to your application.
#override
void initState() {
super.initState();
_userController = StreamController();
Timer.periodic(Duration(seconds: 1), (_) => loadUser());
}
you probably also need to do this only while the app is in foreground. You can use my LifecycleAwareStreamBuilder, there is an example on how to use it here