我试图显示一些从我的应用程序中的服务器拉出的初始数据，我得到的数据，但我无法显示它。这是我的代码，请帮助
必须显示数据的类
import 'package:deep_pocket/models/data_feed.dart';
import 'package:deep_pocket/models/mock_data.dart';
import 'package:deep_pocket/widgets/menu_buttons.dart';
import 'package:deep_pocket/widgets/post_widget.dart';
import 'package:deep_pocket/screens/user_input.dart';
import 'package:flutter/material.dart';
import 'package:flutter/cupertino.dart';
import 'package:provider/provider.dart';
class feedScreen extends StatefulWidget {
static const route = '/feed-screen';
@override
State<feedScreen> createState() => _feedScreenState();
}
class _feedScreenState extends State<feedScreen> {
int filter = 0;
var _intstate = true;
void updateFilter(tx, context) {
setState(() {
filter = tx;
});
Navigator.of(context).pop();
}
@override
void initState() {
// TODO: implement initState
super.initState();
}
@override
void didChangeDependencies() {
if (_intstate) {
Provider.of<mockData>(context).fetchandAddPost();
}
_intstate = false;
// TODO: implement didChangeDependencies
super.didChangeDependencies();
}
void filterSheet(ctx) {
showModalBottomSheet(
context: ctx,
builder: (ctx) => Container(
height: 300,
child: SingleChildScrollView(
child: Container(
height: 280,
child: ListView.builder(
itemCount: Tag.length,
itemBuilder: (ctx, i) => TextButton(
onPressed: () {
return updateFilter(i, context);
},
child: Text(Tag[i]),
)),
)),
));
}
@override
Widget build(BuildContext context) {
return ChangeNotifierProvider<mockData>(
create: (context) => mockData(),
builder: (context, child) {
var posts = context.select((mockData m) => m.items);
print(posts.length);
if (filter != 0) {
posts = posts.where((i) => i.tag == filter).toList();
}
return Scaffold(
// drawer: Drawer(
// // Populate the Drawer in the next step.
// ),
appBar: AppBar(
title: const Text("Home"),
actions: [
TextButton(
onPressed: () => {filterSheet(context)},
child: const Text(
"Filters",
style: TextStyle(color: Colors.white),
))
],
),
body: SingleChildScrollView(
child: Column(
children: [
menuButtons(),
Container(
padding: const EdgeInsets.all(8),
child: ListView.builder(
shrinkWrap: true,
physics: NeverScrollableScrollPhysics(),
itemCount: posts.length,
itemBuilder: (ctx, i) => postWidget(post: posts[i])),
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: () async {
//Waiting for result
var newData =
await Navigator.pushNamed(context, userInput.route);
if (newData != null) {
context.read<mockData>().addPost(newData as dataFeed);
}
},
child: const Icon(Icons.add)),
);
});
}
}
类，我有我的提供者和获取设置
import 'package:deep_pocket/models/data_feed.dart';
import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
class mockData with ChangeNotifier {
List<dataFeed> _data = [
// dataFeed(
// id: DateTime.now().toString(),
// imgsrc: "https://i.pravatar.cc/150?u=a042581f4e29026704d",
// name: "Priyam Srivastava",
// title: "How to change room ?",
// tag: 1,
// text:
// "I would like to know the process of changing my room cause I have not been able to study, and my roomate always plays music and drinks too much then shouts all night, please tell me how",
// ),
// dataFeed(
// id: DateTime.now().toString(),
// imgsrc: "https://i.pravatar.cc/150?u=a042581f4e29026704d",
// title: "Anyone intresed in playing BGMI?",
// name: "Part Agarwal",
// tag: 2,
// text:
// "So I have been looing for a squad for a long time and now i have finally decided that I am gonna buckle up and ask you all to join me",
// ),
// dataFeed(
// id: DateTime.now().toString(),
// imgsrc: "https://i.pravatar.cc/150?u=a042581f4e29026704d",
// title: "How to solve this question in O(n) complexity",
// name: "Preet Singh",
// tag: 3,
// text:
// "So I have been looing for a squad for a long time and now i have finally decided that I am gonna buckle up and ask you all to join me",
// ),
];
List<dataFeed> get items {
return [..._data];
}
Future<void> fetchandAddPost() async {
var url = link;
try {
print("getting your data");
final response = await http.get(url);
final extractedData = json.decode(response.body) as Map<String, dynamic>;
final List<dataFeed> loadedPosts = [];
extractedData.forEach((key, value) {
loadedPosts.add(dataFeed(
id: key,
imgsrc: value['imgsrc'],
name: value['name'],
title: value['title'],
text: value['text'],
date: value['date']));
});
print(loadedPosts.length);
_data = loadedPosts;
print(_data.length);
print("got your data");
notifyListeners();
} catch (e) {
print(e);
// TODO
}
}
Future<void> addPost(dataFeed newpost) async {
var url = link;
try {
final response = await http.post(
url as Uri,
body: json.encode({
'imgsrc': newpost.imgsrc,
'name': newpost.name,
'title': newpost.title,
'text': newpost.text,
'tag': newpost.tag,
'date': newpost.date,
}),
);
final newPost = dataFeed(
id: json.decode(response.body)['name'],
imgsrc: newpost.imgsrc,
name: newpost.name,
title: newpost.title,
text: newpost.text,
tag: newpost.tag,
date: newpost.date);
_data.insert(0, newPost);
notifyListeners();
} catch (e) {
print(e);
// TODO
}
}
}
我正在从服务器获取数据，但它没有显示，如果我添加新数据，它会显示。
这是使用Provider，从网络获取数据，更新ListView和pagination的基本使用年龄。
class ExampleWidget extends StatelessWidget {
const ExampleWidget({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
return ChangeNotifierProvider<ExampleChangeNotifier>(
create: (_) => ExampleChangeNotifier.instance(),
builder: (_, child) {
return Selector<ExampleChangeNotifier, NetworkStatus>(
selector: (_, model) => model.networkStatus,
builder: (_, nStatus, __) => nStatus == NetworkStatus.Loading
? const Center(
child: CircularProgressIndicator(),
)
: nStatus == NetworkStatus.Error
? const Center(
child: Text('Your error widget'),
)
: Selector<ExampleChangeNotifier, int>(
selector: (_, model) => model.listLength,
builder: (_, length, __) => length > 0
? ListView.builder(
itemCount: length + 1,
itemBuilder: (context, index) {
if (index < length) {
var listItem = _.read<ExampleChangeNotifier>().list[index];
return SizedBox(
height: 60,
child: Text('List item: ${listItem.whatever}'),
);
} else {
return Center(
child: ElevatedButton(
onPressed: () {
_.read<ExampleChangeNotifier>().loadMore();
},
child: Selector<ExampleChangeNotifier, bool>(
selector: (_, model) => model.loadMoreRequest,
builder: (_, value, __) => value ? const Text('loading...') : const Text('load more'),
),
),
);
}
},
)
: const Center(
child: Text('No data found'),
),
),
);
},
);
}
}
enum NetworkStatus { Loading, Done, Error }
class ExampleChangeNotifier extends ChangeNotifier {
NetworkStatus _networkStatus = NetworkStatus.Loading;
NetworkStatus get networkStatus => _networkStatus;
final List<dynamic> _list = <dynamic>[];
List<dynamic> get list => _list;
int _listLength = 0;
int get listLength => _listLength;
int _skip = 0; //Send this in your request parameters and use for pagination, e.g (for mysql query) => ... DESC LIMIT _skip, 10
bool _loadMoreRequest = false;
bool get loadMoreRequest => _loadMoreRequest;
ExampleChangeNotifier.instance() {
_getDataFromNetwork();
}
Future<void> _getDataFromNetwork() async {
try {
//Make your http request
// For example : await http.get('https:example.com?skip=$_skip');
_loadMoreRequest = false;
// ... Parse your data
List<dynamic> networkData = <dynamic>[];
_networkStatus = NetworkStatus.Done;
if (networkData.isNotEmpty) {
for (var item in networkData) {
_list.add(item);
_listLength++;
}
}
notifyListeners();
} catch (e) {
_loadMoreRequest = false;
_networkStatus = NetworkStatus.Error;
notifyListeners();
}
}
Future<void> loadMore() async {
_skip = _listLength;
_loadMoreRequest = true;
notifyListeners();
await _getDataFromNetwork();
}
}