Basically I am trying to make an app whose content will be updated with an async function that takes information from a website, but when I do try to set the new state, it doesn't reload the new content. If I debug the app, it shows that the current content is the new one, but after "rebuilding" the whole widget, it doesn't show the new info.
Edit: loadData ( ) method, basically read a URL with http package, the URL contains a JSON file whose content changes every 5 minutes with new news. For example a .json file with sports real-time scoreboards whose scores are always changing, so the content should always change with new results.
class mainWidget extends StatefulWidget
{
State<StatefulWidget> createState() => new mainWidgetState();
}
class mainWidgetState extends State<mainWidget>
{
List<Widget> _data;
Timer timer;
Widget build(BuildContext context) {
return new ListView(
children: _data);
}
#override
void initState() {
super.initState();
timer = new Timer.periodic(new Duration(seconds: 2), (Timer timer) async {
String s = await loadData();
this.setState(() {
_data = <Widget> [new childWidget(s)];
});
});
}
}
class childWidget extends StatefulWidget {
childWidget(String s){
_title = s;
}
Widget _title;
createState() => new childState();
}
class childState extends State<gameCardS> {
Widget _title;
#override
Widget build(BuildContext context) {
return new GestureDetector(onTap: foo(),
child: new Card(child: new Text(_title));
}
initState()
{
super.initState();
_title = widget._title;
}
}
This should sort your problem out. Basically you always want your Widgets created in your build method hierarchy.
import 'dart:async';
import 'package:flutter/material.dart';
void main() => runApp(new MaterialApp(home: new Scaffold(body: new MainWidget())));
class MainWidget extends StatefulWidget {
#override
State createState() => new MainWidgetState();
}
class MainWidgetState extends State<MainWidget> {
List<ItemData> _data = new List();
Timer timer;
Widget build(BuildContext context) {
return new ListView(children: _data.map((item) => new ChildWidget(item)).toList());
}
#override
void initState() {
super.initState();
timer = new Timer.periodic(new Duration(seconds: 2), (Timer timer) async {
ItemData data = await loadData();
this.setState(() {
_data = <ItemData>[data];
});
});
}
#override
void dispose() {
super.dispose();
timer.cancel();
}
static int testCount = 0;
Future<ItemData> loadData() async {
testCount++;
return new ItemData("Testing #$testCount");
}
}
class ChildWidget extends StatefulWidget {
ItemData _data;
ChildWidget(ItemData data) {
_data = data;
}
#override
State<ChildWidget> createState() => new ChildState();
}
class ChildState extends State<ChildWidget> {
#override
Widget build(BuildContext context) {
return new GestureDetector(onTap: () => foo(),
child: new Padding(
padding: const EdgeInsets.symmetric(vertical: 12.0, horizontal: 24.0),
child: new Card(
child: new Container(
padding: const EdgeInsets.all(8.0),
child: new Text(widget._data.title),
),
),
)
);
}
foo() {
print("Card Tapped: " + widget._data.toString());
}
}
class ItemData {
final String title;
ItemData(this.title);
#override
String toString() {
return 'ItemData{title: $title}';
}
}
This was really giving me headache and no Google results were working. What finally worked was so simple. In your child build() assign the value to the local variable before you return. Once I did this everything worked with subsequent data loads. I even took out the initState() code.
Many thanks to #Simon. Your answer somehow inspired me to try this.
In your childState:
#override
Widget build(BuildContext context) {
_title = widget._title; // <<< ADDING THIS HERE IS THE FIX
return new GestureDetector(onTap: foo(),
child: new Card(child: new Text(_title));
}
Hopefully this works in your code. For me, I use a Map for the entire JSON record passed in, rather than a single String, but that should still work.
The Root issue explained
initState(), for the child widget, is called only once when the Widget is inserted into the tree. Because of this, your child Widget variables will never be updated when they change on the parent widget. Technically the variables for the widgets are changing, you are just not capturing that change in your state class.
build() is the method that gets called every time something in the Widget changes. This is the reason #gregthegeek solution works. Updating the variables inside the build method of your child widget will ensure they get the latest from parent.
Works
class ChildState extends State<ChildWidget> {
late String _title;
#override
Widget build(BuildContext context) {
_title = widget._title; // <==== IMPORTANT LINE
return new GestureDetector(onTap: () => foo(),
child: new Text(_title),
);
}
}
Does not work
(It will not update when _title changes in parent)
class ChildState extends State<ChildWidget> {
late String _title;
#override
void initState() {
super.initState();
_title = widget._title; // <==== IMPORTANT LINE
}
#override
Widget build(BuildContext context) {
return new GestureDetector(onTap: () => foo(),
child: new Text(_title),
);
}
}
I'm unsure why this happens when calling setState(...) in an async function, but one simple solution is to use:
WidgetsBinding.instance.addPostFrameCallback((_) => setState(...));
instead of just setState(...)
This fixed my issue... If you have an initial value to be assigned on a variable use it in initState()
Note : Faced this issue when I tried to set initial value inside build function.
#override
void initState() {
count = widget.initialValue.length; // Initial value
super.initState();
}
don't use a future within a future; use different function that will return each future individually like this
List<Requests> requestsData;
List<DocumentSnapshot> requestsDocumentData;
var docId;
#override
void initState() {
super.initState();
getRequestDocs();
}
Future<FirebaseUser> getData() {
var _auth = FirebaseAuth.instance;
return _auth.currentUser();
}
getRequestDocs() {
getData().then((FirebaseUser user) {
this.setState(() {
docId = user.uid;
});
});
FireDb()
.getDocuments("vendorsrequests")
.then((List<DocumentSnapshot> documentSnapshots) {
this.setState(() {
requestsDocumentData = documentSnapshots;
});
});
for (DocumentSnapshot request in requestsDocumentData) {
this.setState(() {
requestsData.add(Requests(
request.documentID,
request.data['requests'],
Icons.data_usage,
request.data['requests'][0],
"location",
"payMessage",
"budget",
"tokensRequired",
"date"));
});
}
}
you can create individual functions for
FireDb().getDocuments("vendorsrequests")
.then((List<DocumentSnapshot> documentSnapshots) {
this.setState(() {
requestsDocumentData = documentSnapshots;
});
});
and
for (DocumentSnapshot request in requestsDocumentData) {
this.setState(() {
requestsData.add(Requests(
request.documentID,
request.data['requests'],
Icons.data_usage,
request.data['requests'][0],
"location",
"payMessage",
"budget",
"tokensRequired",
"date"));
});
}
I found that the use of
this
with setState is must
The real issue on child StatefulWidget not rebuilding is in the KEY
Hey, I'm a bit late to the discussion, but I think this is important.
I was facing a similar problem a while back and I even came to this thread to get some ideas.
In my case, I was simply getting widget.value directly inside the build method of the childWidget, and it was not updating when i called setState in the mainWidget.
Then i found this video: https://youtu.be/kn0EOS-ZiIc
(When to Use Keys - Flutter Widgets 101 Ep. 4) -
Here the Google dev talks about how keys in Flutter.
The short answer is
In a StatefulWidget the actual value you pass is stored in the state, not in the widget itself, like a StatelessWidget does.
When you call setState in the mainWidget, Flutter walks down the widget tree and checks each childWidget's type and key, to see if anything has changed. As stateful widgets store their values in the state, Flutter thinks the child widgets did not change (because the types and keys are the same) and does not rebuild them, even if the value changed.
The real solution is to give the widget a key containing the value that is changing, so when Flutter is walking down the tree, it notices that the key changed, and rebuilds the stateful widget.
Other solutions here may work as well, but if you want to really understand it, this video is worth watching.
first check whether it is a stateless or stateful widget,and if the class is stateless then make it to a stateful widget and try adding a code after closing the
setState(() { _myState = newValue; });
In my case, it was just defining the state as a class property and not a local variable in the build method
Doing this -
List<Task> tasks = [
Task('Buy milk'),
Task('Buy eggs'),
Task('Buy bread'),
];
#override
Widget build(BuildContext context) {
return ListView.builder(
itemBuilder: (context, index) => TaskTile(
...
instead of this -
#override
Widget build(BuildContext context) {
List<Task> tasks = [
Task('Buy milk'),
Task('Buy eggs'),
Task('Buy bread'),
];
return ListView.builder(
itemBuilder: (context, index) => TaskTile(
...
Found the best solution.
If you are using a stateless widget you can't use set state, so just convert the stateless widget to statefull widget
Related
I was Learning Async and Future Functions in Dart but I got confused because I still not get it like how print("object") is compiled before getData() function because traditionally next Line is read by compiler once the before line or Function is fully compiled/Executed . If I am making a Mistake Please correct me out , I am noob tbh
import 'package:flutter/material.dart';
class Loading extends StatefulWidget {
const Loading({super.key});
#override
State\<Loading\> createState() =\> \_LoadingState();
}
class \_LoadingState extends State\<Loading\> {
void getdata() async {
String parth = await Future.delayed(Duration(seconds: 3), () {
return 'parth';
});
print('Hey');
print(parth);
}
#override
int count = 0;
void initState() {
// TODO: implement initState
super.initState();
getdata();
print('object');
}
#override
Widget build(BuildContext context) {
// print(' Setstae vala + $count');
return Scaffold(
appBar: AppBar(
title: Text('Loading'),
),
body: ElevatedButton(
onPressed: () {
setState(() {
count++;
});
},
child: Text('$count')),
);
}
}
Your output should be like this:
object
Hey
parth
because traditionally next Line is read by compiler once the before
line or Function is fully compiled/Executed
Normaly, yes. But since you are using the async keyword in this case, it works a little differently.
What happens here:
You call getData first in your initState. In getData you have a future delayed in it, which you wait for with keywoard await. So it waits 3 seconds until you return 'parth' as a string. At the same time, however, it continues to run in your initState to return 'object'.
getdata is a async method, you need to return Future<void> to await.
Now the initState() cant be async, you can create another method to await and place it here.
void newMethod() async {
await getdata();
print('object');
}
And place newMethod() inside initState.
Or you can use .then
getdata().then((_) {
print('object');
});
My problem is with Futures, because they should be obtained before build() method executed, as the documentation states:
The future must be obtained earlier, because 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.
I know that Futures should be called in initstate() function before the build method executed, but my case is different.
I want to get data from api as a Future, but the request I am sending to the api needs some parameters that user should select inside the screen's build() method.
And I don't know what the parameter of the request will be until user selects in build() method, and I have to call the api in the build() method and use FutureBuilder there, but that makes FutureBuilder to get constantly called, and I don't want that.
basically, I don't want to call FutureBuilder indefinetely, and I can't put my Future inside initState() because the Future needs some parameters that user later selects when the screen is shown inside build() method.
inside the build method:
FutureBuilder<List<LatLng>>(
builder: (context, snapshot) {
if (snapshot.hasData) {
return PolylineLayer(
polylines: [
Polyline(
points: snapshot.data!,
strokeWidth: 4,
color: Colors.purple),
],
);
} else if (snapshot.hasError) {
return Text("${snapshot.error}");
} else {
return Container();
}
},
future: Provider.of<NavigationProvider>(context)
.getNavigationPoints(pointToGoTo!),
),
now if you look at the code, at the final lines, I am sending the parameter pointToGoTo to the function which calls the backend.
simply, I want to get rid of calling api and getting data back as a Future inside build method, I want to do it in initState or somewhere else that prevents the build methods calling backend indefinitely.
is there any way to fix this problem?
Thanks in advance.
Firstly, create future state variable and a nullable params and use it with conditional if while using FutureBuilder.
I will recommend checking Fixing a common FutureBuilder and StreamBuilder problem
Now you can follow this example. It is missing progressBar on API recall, StreamBuilder might be better option in cases like this.
class Foo extends StatefulWidget {
const Foo({super.key});
#override
State<Foo> createState() => _FooState();
}
class _FooState extends State<Foo> {
int? params;
Future<int> fetch(int? data) async {
await Future.delayed(Duration(seconds: 1));
return (params ?? 0) * 2;
}
late Future<int> future = fetch(params);
#override
Widget build(BuildContext context) {
return Scaffold(
body: Column(
children: [
DropdownButton<int?>(
value: params,
items: List.generate(
12,
(index) => DropdownMenuItem(
value: index,
child: Text("$index"),
)).toList(),
onChanged: (value) {
future =
fetch(params); // this will only call api with update data
setState(() {
params = value;
});
},
),
if (params != null)
FutureBuilder<int>(
future: future,
builder: (context, snapshot) {
if (snapshot.hasData) return Text("${snapshot.data}");
return CircularProgressIndicator();
},
)
],
),
);
}
}
class Testing extends StatefulWidget {
const Testing({super.key});
#override
State<Testing> createState() => _TestingState();
}
class _TestingState extends State<Testing> {
bool isFetched = false;
#override
Widget build(BuildContext context) {
return Scaffold(
body: Consumer<SomethingProvider>(
builder: (context, prov, child) {
if (!isFetched) {
prov.getData("a", "b");
Future.delayed(const Duration(milliseconds: 200), () {
isFetched = true;
});
}
if (prov.newData.isNotEmpty) {
return Column(
// make widget tree from here
);
} else {
return const Center(
child: CircularProgressIndicator(),
);
}
},
),
);
}
}
class SomethingProvider extends ChangeNotifier {
List newData = [];
Future getData(param1, param2) async {
newData = ["testingdata"];
}
}
I made it possible to toggle the heart icon in the post like Instagram.
And I implemented it so that user information is uploaded to the firestore when I toggle the icon.
There is no problem with the 'Like' and 'Unlike' function of 'Like Icon', but there is one other problem.
There is a problem that the color of the icon does not change immediately when toggling the icon in the post. I can check that this icon has changed when I go to a different screen and come back in.
The following is the code for this icon. (I edited this code)
class LikeToggleIcon extends StatefulWidget {
final String postKey;
final PostModel postModel;
const LikeToggleIcon(
{Key key,
this.postKey,
this.postModel,
this.fromSearch,
this.searchResults})
: super(key: key);
#override
State<LikeToggleIcon> createState() => _LikeToggleIconState();
}
class _LikeToggleIconState extends State<LikeToggleIcon> {
// bool _isLiked = false;
#override
Widget build(BuildContext context) {
//get userModel
UserModel userModel =
Provider.of<UserModelState>(context, listen: false).userModel;
return IconButton(
onPressed: () {
// setState(() {
postNetworkRepo.toggleLike(
widget.postModel.postKey, userModel.userKey);
// });
},
icon: Icon(
widget.postModel.numOfLikes.contains(userModel.userKey)
? Icons.favorite_outlined
: Icons.favorite_border_outlined,
size: 27,
color: Colors.redAccent,
),
);
//toggle method
class PostNetworkRepo with Transformers {
Future<void> toggleLike(String postKey, String userKey) async {
final DocumentReference postRef =
Firestore.instance.collection(COLLECTION_POSTS).document(postKey);
final DocumentSnapshot postSnapshot = await postRef.get();
//check Post collection
if (postSnapshot.exists) {
//check already contain userKey
//if no contain upload userKey, else delete userKey (toggle Like/Unlike)
if (postSnapshot.data[KEY_NUMOFLIKES].contains(userKey)) {
postRef.updateData({
KEY_NUMOFLIKES: FieldValue.arrayRemove([userKey])
});
} else {
postRef.updateData({
KEY_NUMOFLIKES: FieldValue.arrayUnion([userKey])
});
}
}
}
}
PostNetworkRepo postNetworkRepo = PostNetworkRepo();
//This is the part of detail post screen.
class DetailScreen extends StatefulWidget {
#override
_DetailScreenState createState() => _DetailScreenState();
}
class _DetailScreenState extends State<DetailScreen> {
#override
Widget build(BuildContext context) {
//get userModel
UserModel userModel =
Provider.of<UserModelState>(context, listen: false).userModel;
return Scaffold(
appBar: AppBar(
title: _postUser(),
actions: [
//toggle likeIcon
LikeToggleIcon(
postKey: widget.postKey,
postModel: widget.postModel,
),
],
),
I tried using setState() on the IconButton(), but the problem was not solved.
can I get help with this problem?
I believe you are using setState() to change value of variable that's inside the Widget and NOT the State of that widget.
You need to have variables that changes the Widget inside the state for it to be updated. Keeping it inside Widget won't change the Icon, unless the whole widget is recreated (like when you change the screen).
(correct me if I'm wrong. Providing full code of the widget could be more useful)
I'm trying to display a comment stream from Reddit API. I"m using Streambuilder to stream contents as it arrives and displays it as list view thing is I can only view present stream content and this will disappear as new stream contents appear replacing the old ones. If I don't mention item count inside listview.builder prints contents infinitely still new stream appears.
is there a way to display contents along with previous contents in a scrollable fashion and automatically scroll down as a new stream message appears??
Assuming that the comment stream returns individual (and preferably unique) comments one at a time rather than as a list, what you need to do is store the incoming comments in a state object such as a list. When a new comment comes through the stream, you add it to the list and then trigger a widget rebuild.
What you are doing right now is replacing state with each new stream element rather than accumulating them. Using the code you provided, I have edited it to behave as an accumulator instead. Notice the List<Comment> comments = <Comment>[] object added to state. I have also removed the StreamBuilder since that isn't helpful for this use case.
import 'package:flutter/material.dart';
import 'dart:async';
import 'package:draw/draw.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
home: RedditFlutter(),
debugShowCheckedModeBanner: false,
);
}
}
class RedditFlutter extends StatefulWidget {
RedditFlutter({Key key}) : super(key: key);
#override
_RedditFlutterState createState() => _RedditFlutterState();
}
class _RedditFlutterState extends State<RedditFlutter> {
var comments;
ScrollController _scrollController =
new ScrollController(initialScrollOffset: 50.0);
List<Comment> comments = <Comment>[];
StreamSubscription<Comment>? sub;
var msg = '';
Future<void> redditmain() async {
// Create the `Reddit` instance and authenticated
Reddit reddit = await Reddit.createScriptInstance(
clientId: 'clientid',
clientSecret: 'clientsecret',
userAgent: 'useragent',
username: 'username',
password: 'password', // Fake
);
// Listen to comment stream and accumulate new comments into comments list
sub = reddit.subreddit('cricket').stream.comments().listen((comment) {
if (comment != null) {
// Rebuild from state when a new comment is accumulated
setState(() {
comments.add(comment);
})
}
});
}
#override
void initState() {
// TODO: implement initState
redditmain();
super.initState();
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Reddit"),
centerTitle: true,
),
body: Center(
child: Container(
child: ListView.builder(
controller: _scrollController,
itemCount: comments.length,
itemBuilder: (context, index) {
final Comment comment = comments[index];
return Card(
child: ListTile(
leading: Image.asset('assets/criclogo.png'),
title: Text(comment.body),
trailing: Icon(Icons.more_vert),
),
);
},
),
);
),
);
}
#override
void dispose() {
sub?.cancel();
super.dispose();
}
}
Note that I have not tested this code so there may be (trivial) bugs. Still, conceptually, it should be fine.
I am building an app which has local database and I keep some infos about movies in that database. There is a screen called "Favorites" where I get the movies from local database and put them in a listview:
And if I click any movie from that list, I will be directed to a new Screen where I can see movie details. In this screen, there is a button which removes the movie from local database.
Now my problem starts here: After I remove any movie from database and go back to "Favorites" Screen, I still see that movie in ListView. But I have already removed that movie from database. If I was doin this on Android platform, I would override onStart method and make a query to database, then update the listview. But in Flutter as long as I know, there is no method as onStart. So, what should I do?
class FavoritesScreen extends StatefulWidget {
#override
_FavoritesScreenState createState() => _FavoritesScreenState();
}
class _FavoritesScreenState extends State<FavoritesScreen> {
var favoriteMovieDatabase = FavoriteMovieDatabase();
List<MovieOverview> movieOverviewList = List<MovieOverview>();
#override
void initState() {
super.initState();
favoriteMovieDatabase
.getAllFavoriteMovies()
.then((List<MovieOverview> list) {
setState(() {
movieOverviewList = list;
});
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text("Favorites")),
body: MovieOverviewListView(movieOverviewList, "FAVORITE")
);
}
}
EDIT:
I have tried to use WidgetsBindingObserver but it did not help.
#override
void didChangeAppLifecycleState(AppLifecycleState state) {
super.didChangeAppLifecycleState(state);
if(state == AppLifecycleState.resumed){
favoriteMovieDatabase
.getAllFavoriteMovies()
.then((List<MovieOverview> list) {
setState(() {
movieOverviewList = list;
});
});
}
}
It did not even call this method.
As a simple solution, you can await the result of a navigator push:
goToDetailPage(BuildContext context) async {
await Navigator.of(context).pushNamed('movieDetail');
// this is reached when the route is popped
reloadData();
}
To make the code even more efficient, you can return a result from your detail route that signifies if the movie was deleted:
Navigator.pop(context, 'MOVIE_DELETED');
and
goToDetailPage(BuildContext context) async {
final result = await Navigator.of(context).pushNamed<String>('movieDetail');
if(result == 'MOVIE_DELETED') {
reloadData();
}
}
In the long run, when there are more ways to change the database content (think of a semitransparent dialog where the movie list is still visible in background, or live updates), it would be better to move to some kind of reactive architecture similar to Room on Android.
Assuming your problem happens when you use Navigator to push a new route, then you can use RouteAware mixin combined with RouteObserver and then overrides didPopNext method.
didPopNext is called whenever a route becomes visible again.
final RouteObserver<PageRoute> routeObserver = new RouteObserver<PageRoute>();
void main() {
runApp(new MaterialApp(
home: new Container(),
navigatorObservers: [routeObserver],
));
}
class RouteAwareWidget extends StatefulWidget {
State<RouteAwareWidget> createState() => new RouteAwareWidgetState();
}
// Implement RouteAware in a widget's state and subscribe it to the RouteObserver.
class RouteAwareWidgetState extends State<RouteAwareWidget> with RouteAware {
#override
void didChangeDependencies() {
super.didChangeDependencies();
routeObserver.subscribe(this, ModalRoute.of(context));
}
#override
void dispose() {
routeObserver.unsubscribe(this);
super.dispose();
}
#override
void didPopNext() {
// TODO: query DB again
}
#override
Widget build(BuildContext context) => new Container();
}
You can achieve this with the initState:
#override
void initState() {
_doWhatYouWantToDo().then((value){
print('Async done');
});
super.initState();
}
add these code when you want to run method on pop
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => ConversationScreen() ,
)).then((value) {
//add your method which you want to run on pop!! cheers
setState(() {});
});
},