While fetching data from database in flutter snapShot.ConnectionState is always waiting and the circular progress indicator keeps on loading.
I am not getting any errors and I am using FutureBuilder to build my widget.
Class where I build my widget
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import '../providers/event_provider.dart';
class HomeScreen extends StatelessWidget {
#override
Widget build(BuildContext context) {
return FutureBuilder(
future: Provider.of<EventProviders>(context).fetchAndSetEvents(),
builder: (ctx, dataSnapshot) {
if (dataSnapshot.connectionState == ConnectionState.waiting) {
return Center(
child: CircularProgressIndicator(),
);
} else {
return Consumer<EventProviders>(
child: Text('Not found'),
builder: (ctx, eventData, ch) {
if (eventData.events.length <= 0) {
return ch;
} else {
return ListView.builder(
itemCount: eventData.events.length,
itemBuilder: (ctx, index) {
return Container(
child: Text(eventData.events[index].eventName),
);
},
);
}
},
);
}
},
);
}
}
My future class
Future<void> fetchAndSetEvents() async {
final dataList = await DBHelper.getData('user_events');
_events = dataList
.map(
(data) => EventProvider(
eventName: data['event'],
eventDate: data['date'],
id: data['id'],
),
)
.toList();
notifyListeners();
}
}
Some help will be highly appreciated
Set listen: false
future: Provider.of<EventProviders>(context, listen: false).fetchAndSetEvents(),
Related
I am getting error The method '[]' can't be unconditionally invoked because the receiver can be 'null'.
Mydata inside _categoriesList future
[
{
"business_category_id": 1,
"business_category": "Manufacturer",
"business_category_image": "164423936662011a06c450d.png"
},
{
"business_category_id": 2,
"business_category": "Distributor",
"business_category_image": "164423937762011a11033aa.png"
},
{
"business_category_id": 3,
"business_category": "Wholesaler",
"business_category_image": "164423938762011a1bb2e3c.png"
},
{
"business_category_id": 4,
"business_category": "Retailer",
"business_category_image": "164423940062011a28189e5.png"
},
{
"business_category_id": 5,
"business_category": "Reseller",
"business_category_image": "164423941362011a3554148.png"
},
{
"business_category_id": 6,
"business_category": "Service Provider",
"business_category_image": "164423942462011a4096996.png"
}
]
my code inside futurebuilder. I am having problem accessing snapshot.data[index]
FutureBuilder(
future: _categoriesList,
builder: (_, snapshot) {
if (snapshot.hasData) {
return ListView.builder(
itemCount: 6,
itemBuilder: (_, index) {
return Text(snapshot.data[index]); // error The method '[]' can't be unconditionally invoked because the receiver can be 'null'
});
}
},
)
Here is the example for ListView.builder:
import 'dart:async';
import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
Future <List<Data>> fetchData() async {
final response =
await http.get('https://jsonplaceholder.typicode.com/albums');
if (response.statusCode == 200) {
List jsonResponse = json.decode(response.body);
return jsonResponse.map((data) => new Data.fromJson(data)).toList();
} else {
throw Exception('Unexpected error occured!');
}
}
class Data {
final int userId;
final int id;
final String title;
Data({this.userId, this.id, this.title});
factory Data.fromJson(Map<String, dynamic> json) {
return Data(
userId: json['userId'],
id: json['id'],
title: json['title'],
);
}
}
void main() => runApp(MyApp());
class MyApp extends StatefulWidget {
MyApp({Key key}) : super(key: key);
#override
_MyAppState createState() => _MyAppState();
}
class _MyAppState extends State<MyApp> {
Future <List<Data>> futureData;
#override
void initState() {
super.initState();
futureData = fetchData();
}
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter API and ListView Example',
home: Scaffold(
appBar: AppBar(
title: Text('Flutter ListView'),
),
body: Center(
child: FutureBuilder <List<Data>>(
future: futureData,
builder: (context, snapshot) {
if (snapshot.hasData) {
List<Data> data = snapshot.data;
return
ListView.builder(
itemCount: data.length,
itemBuilder: (BuildContext context, int index) {
return Container(
height: 75,
color: Colors.white,
child: Center(child: Text(data[index].title),
),);
}
);
} else if (snapshot.hasError) {
return Text("${snapshot.error}");
}
// By default show a loading spinner.
return CircularProgressIndicator();
},
),
),
),
);
}
}
Specify your data-type for list in FutureBuilder first.
FutureBuilder<List<String>>()
//
Check if you are getting data. print the data using snapshot.data.
FutureBuilder<List<String>>(
future: _categoriesList,
builder: (_, snapshot) {
if (snapshot.hasData) {
print("snapshot:: data >>>> ${snapshot.data}");
return ListView.builder(
itemCount: 6,
itemBuilder: (_, index) {
return Text(snapshot.data[index]); // error The method '[]' can't be unconditionally invoked because the receiver can be 'null'
});
}
},
)
Assuming you have a Category class, with variables for the CategoryId,CategoryName,CategoryImage with all the needed methods as shown in https://stackoverflow.com/a/71029334/12371668
//create an instance of the category class before the build() method
final category = Category();
#override
Widget build(BuildContext context) {
// other code
FutureBuilder(
future: category.fetchData(),
builder: (context, snapshot) {
if (snapshot.hasData) {
List<Category> categories = snapshot.data();
return ListView.builder(
itemCount: categories.length,
itemBuilder: (context, index) {
var category = categories[index];
return Text(category.CategoryName);
});
}
},
)
}
The entry point is _processError function. I expect to get a widdet there. And this _processError runs from a parent FutureBuilder.
Then another Future builder should be executed, at least I think it should... But it seems there is no result from there. Whats wrong with it?
FutureBuilder<List<ShortLetter>>(
future: fetchMessages(),
builder: (BuildContext context, AsyncSnapshot<List<ShortLetter>> snapshot) {
...
} else if (snapshot.hasError) {
return _processError(snapshot, context); // I want to get a widget when an error happens
...
},
);
Future<bool> checkConnection() async {
debugPrint('---checkConnection---');
var connectivityResult = await (Connectivity().checkConnectivity());
...
// and returs true or false
}
Widget _processError(AsyncSnapshot snapshot, BuildContext context) {
var errorType = snapshot.error.runtimeType;
debugPrint('AllMessagesView, snapshot error: $errorType');
debugPrint(snapshot.error.toString());
if (errorType == TimeoutException) {
debugPrint('0000000000000000');
//////////////////////////////////////////////////////
// there is any output in console from the FutureBuilder below
// but checkConnection() was executed
FutureBuilder<bool>(
future: checkConnection(),
builder: (BuildContext context, AsyncSnapshot<bool> snapshot) {
if (snapshot.hasData) {
debugPrint('11111111111111 snapshot data: ${snapshot.data}');
if (snapshot.data == true) {
...
}
...
} else if (snapshot.hasError) {
debugPrint('2222222222222');
...
} else {
debugPrint('Error. This should not happen.');
...
}
},
);
...
}
...
}
here is a sample console output and any result from the second FutureBuilder
I/flutter (10556): AllMessagesView, snapshot error: TimeoutException
I/flutter (10556): TimeoutException after 0:00:10.000000: Future not completed
I/flutter (10556): 0000000000000000
I/flutter (10556): ---checkConnection---
Parent FutureBuilder is already been processed, I think we don't need to pass Async data.
This demo widget may help.
class MyApp extends StatefulWidget {
const MyApp({Key? key}) : super(key: key);
#override
State<MyApp> createState() => _MyAppState();
}
class _MyAppState extends State<MyApp> {
Future<int> parentF() async {
return await Future.delayed(Duration(seconds: 2), () => 4);
}
Future<String> childF(int sec) async {
return await Future.delayed(Duration(seconds: sec), () => "got the child");
}
Widget childFB(final data) {
print(data.runtimeType);
return FutureBuilder(
future: childF(4),
builder: (context, snapshot) => snapshot.hasData
? Text("${snapshot.data!} parent data: $data ")
: const Text("loading second child"));
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: Column(
children: [
FutureBuilder(
future: parentF(),
builder: (context, parentSnapshot) {
return parentSnapshot.hasData
? FutureBuilder<String>(
future: childF(3),
builder: (context, snapshot) {
return snapshot.hasData
? Text(
"${snapshot.data!} parent data: ${parentSnapshot.data} ")
: const Text("loading child");
},
)
: const Text("loading parent");
},
),
FutureBuilder(
future: parentF(),
builder: (context, parentSnapshot) {
return parentSnapshot.hasData
? childFB(parentSnapshot
.data) // it already have normal data, not async
: const Text("loading parent");
},
),
],
));
}
}
I have method like this in my provider file to get a list of items :
Future<void> getServerMeals() async {
final QueryBuilder<ParseObject> parseQuery =
QueryBuilder<ParseObject>(ParseObject('UsersEaten'));
final ParseResponse apiResponse = await parseQuery.query();
if (apiResponse.success && apiResponse.results != null) {
List<dynamic>? apiRes = apiResponse.results;
List<EatenItem> newMeals = apiRes!
.map((e) => EatenItem(
id: e['objectId'],
eatenCal: e['eatenCal'],
eatenTitle: e['eatenTitle'],
eatenImageUrl: e['eatenImg'],
userId: e['objectId'],
))
.toList();
_eatenMeals = newMeals;
print(apiResponse.results);
notifyListeners();
}
}
and in my main screen I have a StatelessWidget and FutureBuilder to get that list :
class TimelineWidget extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Column(
mainAxisAlignment: MainAxisAlignment.start,
children: [
Container(
child: FutureBuilder(
future: Provider.of<EatenMeals>(context, listen: false).getServerMeals(),
builder: (ctx, snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return Center(
child: CircularProgressIndicator(),
);
}
return Consumer<EatenMeals>(
builder: (ctx, mealsList, child) => ListView.builder(
itemCount: mealsList.eatenMeals.length,
itemBuilder: (ctx, index) =>
DailyEaten(mealsList.eatenMeals[index]),
),
);
},
),
),
],
);
}
as you can see there is nothing in my build method and I've tried to use Consumer as future to avoid infinite loop but it doesn't work for me please tell me what's wrong here I appreciate if u explain with code snippet
At first, when i started writing my calls to get data from firestore, it worked. But when i tried writing more docs to my collection, it failed to bring data for the docs i recently added. Then, when i deleted the first one i added, i stopped receiveing data from firestore all together. I have tried several methods, but have all ended in failure.
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/material.dart';
class collect extends StatefulWidget {
#override
_collectState createState() => _collectState();
}
class _collectState extends State<collect>
{
Future _data;
void initState()
{
super.initState();
_data = getStuff();
}
Future getStuff()
async {
var firestore = FirebaseFirestore.instance;
QuerySnapshot qn = await firestore.collection("buses").get();
return qn.docs;
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: FutureBuilder(
future: _data,
builder: (_, snapshot)
{
if(snapshot.connectionState == ConnectionState.waiting)
{
return Center(
child:Text("Loading")
);
}
else if(snapshot.connectionState == ConnectionState.done)
{
return ListView.builder(itemCount: snapshot.data.length,itemBuilder:(_, index)
{
return Container(
child: ListTile(
title: Text(snapshot.data[index].data()["name"].toString()),
subtitle: Text(snapshot.data[index].data()["price"].toString()),
),
);
});
}
},
),
);
}
}
```
Define your database call as,
Future getStuff() async {
var docs;
await FirebaseFirestore.instance
.collection("buses")
.get()
.then((querySnapshot) {
docs = querySnapshot.docs;
});
return docs;
}
Then use the FutureBuilder in the build() function as,
return Scaffold(
body: Center(
child: FutureBuilder<dynamic>(
future: getStuff(),
builder: (BuildContext context, AsyncSnapshot<dynamic> snapshot) {
if (snapshot.hasData) {
return ListView.builder(
itemCount: snapshot.data.length,
itemBuilder: (_, index) {
return Container(
child: ListTile(
title: Text(
snapshot.data[index].data()["name"].toString()),
subtitle: Text(
snapshot.data[index].data()["price"].toString()),
),
);
});
} else {
return CircularProgressIndicator();
}
},
),
),
);
I wrapped the FutureBuilder inside a Center just for clarity, you may remove that Center widget.
Want to create a list view from live data from server using stream,
so create fake stream of data and then save its snapshot in a list to test result, when use that list in ListTile and run app get following error:
The following assertion was thrown building ListTile(dirty):
No Material widget found.
ListTile widgets require a Material widget ancestor.
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
home: SafeArea(
child: Center(
child: StreamBuilderPage(),
),
),
);
}
}
class StreamBuilderPage extends StatefulWidget {
#override
_StreamBuilderPageState createState() => _StreamBuilderPageState();
}
class _StreamBuilderPageState extends State<StreamBuilderPage> {
List<int> items = [];
#override
Widget build(BuildContext context) {
return StreamBuilder(
//Error number 2
stream: NumberCreator().stream,
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return CircularProgressIndicator();
} else if (snapshot.connectionState == ConnectionState.done) {
return Text('done');
} else if (snapshot.hasError) {
return Text('Error!');
} else {
items.add(snapshot.data);
print(items); //print every second: [0] then [0,1] then [0,1,2] ...
return ListView.builder(
itemBuilder: (context, index) {
return ListTile(
title: Text(items[index].toString()),
);
},
itemCount: items.length,
);
}
},
);
}
}
class NumberCreator {
NumberCreator() {
Timer.periodic(Duration(seconds: 1), (timer) {
//add count to stream
_controller.sink.add(_count);
_count++;
});
}
var _count = 1;
final _controller = StreamController<int>();
Stream<int> get stream => _controller.stream;
dispose() {
_controller.close();
}
}
What actually cause this error?
Thanks community.
Try this
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
home: StreamBuilderPage(),
);
}
}
class StreamBuilderPage extends StatefulWidget {
#override
_StreamBuilderPageState createState() => _StreamBuilderPageState();
}
class _StreamBuilderPageState extends State<StreamBuilderPage> {
List<int> items = [];
#override
Widget build(BuildContext context) {
return Scaffold(
body: SafeArea(
child: Center(
child: StreamBuilder(
//Error number 2
stream: NumberCreator().stream,
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return CircularProgressIndicator();
} else if (snapshot.connectionState == ConnectionState.done) {
return Text('done');
} else if (snapshot.hasError) {
return Text('Error!');
} else {
items.add(snapshot.data);
print(
items); //print every second: [0] then [0,1] then [0,1,2] ...
return ListView.builder(
itemBuilder: (context, index) {
return ListTile(
title: Text(items[index].toString()),
);
},
itemCount: items.length,
);
}
},
),
),
),
);
}
}
class NumberCreator {
NumberCreator() {
Timer.periodic(Duration(seconds: 1), (timer) {
//add count to stream
_controller.sink.add(_count);
_count++;
});
}
var _count = 1;
final _controller = StreamController<int>();
Stream<int> get stream => _controller.stream;
dispose() {
_controller.close();
}
}
I think you have to embed ListTile in a Material specific widget such as scaffold. I had a similar issue a few days ago and somewhere the message tells you which widgets may be wrapped around to prevent this error
StreamBuilder(
//Error number 2
stream: FunctionWhichReturnSomething().stream,
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return CircularProgressIndicator();
} else if (snapshot.connectionState == ConnectionState.done) {
return Text('done');
} else if (snapshot.hasError) {
return Text('Error!');
} else {
items.add(snapshot.data);
print(
items); //print every second: [0] then [0,1] then [0,1,2] ...
return ListView.builder(
itemBuilder: (context, index) {
return ListTile(
title: Text(items[index].toString()),
);
},
itemCount: items.length,
);
}
},
)