在此 <UserData>myorder 小部件上方找不到正确的提供程序<列表>

Question

我试图使用流提供程序读取数据，但我得到了错误：

错误：找不到正确的提供程序<列表>在此myorder Widget之上

发生这种情况是因为您使用了不包括提供程序的BuildContext由您选择。有几个常见的场景：

• 您在main.dart中添加了一个新的提供程序，并执行了热重新加载。若要修复此问题，请执行热重新启动

• 您试图读取的提供程序处于不同的路径

提供者是"；scoped"；。因此，如果在路由中插入提供者，那么其他路由将无法访问该提供商。

• 您使用的BuildContext是您尝试读取的提供程序的祖先

确保myorder在您的MultiProvider/Provider之下<列表>。当您创建一个提供程序并尝试立即读取它时，通常会发生这种情况。

例如，而不是：

void main() async {
WidgetsFlutterBinding.ensureInitialized();
await Firebase.initializeApp();
final firestoreservice _db= firestoreservice();
runApp(
MultiProvider (
providers:[
ChangeNotifierProvider(
create:(context)=>productstore(),),
ChangeNotifierProvider(
create:(context)=>selectedDropdownItems(),),
ChangeNotifierProvider(
create:(context)=>userprovider(),),
ChangeNotifierProvider(
create:(context)=>uploadProd()),
StreamProvider(create: (BuildContext context)=>_db.getUserList(), initialData: null,)
],
//ChangeNotifierProvider(
//create:(context)=>productstore(),
child: MaterialApp(
debugShowCheckedModeBanner: false,
title: 'ROW',
theme: ThemeData(
primarySwatch: Colors.red,
),
home:users(),
),
),
);
}
class UserData {
UserData ({ this.email,this.id,this.password,this.name});
String? email;
String? id;
String? password;
String? name;

UserData.fromJson(Map<String, dynamic> parsedJSON)
:name = parsedJSON['name'],
email = parsedJSON['email'];
}
class firestoreservice {
FirebaseFirestore _db = FirebaseFirestore.instance;
Stream<List<UserData>> getUserList() {
return _db.collection('users')
.snapshots()
.map((snapshot) =>
snapshot.docs
.map((document) => UserData.fromJson(document.data())).toList()
);
}

}
class users extends StatelessWidget{
@override
Widget build(BuildContext context) {
var store = Provider.of<List<UserData>>(context,listen:false);

return  Container(
width: MediaQuery.of(context).size.width,
height: MediaQuery.of(context).size.height,
decoration: BoxDecoration( color: Colors.white,
// border: Border.all(color: Colors.red)
),
child:
ListView(
children: [
Column(
children: [
Padding(
padding: const EdgeInsets.only(top: 4.0,bottom: 4.0),
),
ListView.builder(
shrinkWrap: true,
physics: ScrollPhysics(),

itemCount:store.length,
itemBuilder:(context, index)
{UserData userdata= store[index];
return Padding(
padding: const EdgeInsets.only(top: 4.0,bottom: 4.0),
child: Container(
height: 220,
width: MediaQuery.of(context).size.width,
decoration: BoxDecoration(
boxShadow: [
BoxShadow(
color: Colors.black,
blurRadius: 2.0,
spreadRadius: 0.0,
offset: Offset(2.0, 2.0),
)
],
color: Colors.white,
//border: Border.all(color: Colors.red)
),
child: Column(
children: [
Row(
//mainAxisAlignment: MainAxisAlignment.center,
children: [
Padding(
padding: const EdgeInsets.only(top: 4.0,bottom: 4.0,left: 10.0),

child: Text(userdata.name.toString(),style: TextStyle(color: Colors.red,fontSize: 10, fontWeight: FontWeight.bold),),
),
Padding(
padding: const EdgeInsets.only(top: 4.0,bottom: 4.0,left: 10.0),

child: Text(userdata.email.toString(),style: TextStyle(color: Colors.red,fontSize: 10, fontWeight: FontWeight.bold),),
),

],
),

],
),
),
);
}
),
],
),
],
)
,
);

}
}

Answer 1

检查这个例子，这是UI文件：

import 'package:custom/second.dart';
import 'package:custom/second.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MultiProvider(
providers: [ChangeNotifierProvider(create: (context) => UserProvider())],
child: MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key? key, required this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: ListView.builder(
itemCount: context.watch<UserProvider>().list.length,
itemBuilder: (context, index) => ListTile(
title:
Text("${context.watch<UserProvider>().list[index].name}"),
subtitle:
Text("${context.watch<UserProvider>().list[index].email}"),
)),
floatingActionButton: FloatingActionButton(
onPressed: () => context
.read<UserProvider>()
.setUser(User("demo2", "[e-mail]")),
child: Icon(Icons.add),
),
);
}
}

这是这个列表的Provider文件

import 'package:flutter/cupertino.dart';
class UserProvider extends ChangeNotifier {
List<User> _list = [User("User", "[e-mail]")];
List<User> get list => _list;
setUser(User value) {
_list.add(value);
notifyListeners();
}
}
class User {
String name;
String email;
User(this.name, this.email);
}