错误：在此<NewUser> UpdateSupervisor 小组件上方找不到正确的提供程序

Question

如何在onPressed函数中包装流提供程序？这是我的课。

UpdateSupervisor类

import 'package:finalyearproject/model/NewUser.dart';
import 'package:finalyearproject/service/database.dart';
import 'package:finalyearproject/shared/Loading.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

class UpdateSupervisor extends StatefulWidget {

@override
_UpdateSupervisorState createState() => _UpdateSupervisorState();
}
class _UpdateSupervisorState extends State<UpdateSupervisor> {
// form values
String name;
String email;
String uniqueID;
String phone;
String id;

final GlobalKey<FormState> _formKey = GlobalKey();
@override
Widget build(BuildContext context) {
final user = Provider.of<NewUser>(context);
return Scaffold(
appBar: AppBar(
title: Text('Edit Supervisor'),
backgroundColor: Colors.redAccent,
),
body: StreamBuilder(
stream: DatabaseService(uid: user.id).userData,
builder: (context, snapshot){
if(!snapshot.hasData){
return Loading();
}
NewUser userData = snapshot.data;
return Form(
key: _formKey,
child: SingleChildScrollView(
padding: const EdgeInsets.all(16.0),
child: Column(
crossAxisAlignment: CrossAxisAlignment.end,
children: <Widget>[
SizedBox(height: 25.0),
TextFormField(
decoration: InputDecoration(
hintText: 'Name',
border: OutlineInputBorder(borderRadius: BorderRadius.circular(5))),
keyboardType: TextInputType.text,
initialValue: userData.name,
validator: (value) => value.isEmpty ? 'Name cannot be empty!': null,
onChanged: (value) {
setState(() => name = value);
},
),
SizedBox(height: 10.0),
TextFormField(
decoration: InputDecoration(
hintText: 'Email',
border: OutlineInputBorder(borderRadius: BorderRadius.circular(5))),
keyboardType: TextInputType.emailAddress,
validator: (value) => value.isEmpty ? 'Email cannot be empty!': null,
onChanged: (value) {
setState(() => email = value);
},
),
SizedBox(height: 10.0),
TextFormField(
decoration: InputDecoration(
hintText: 'Number Phone',
border: OutlineInputBorder(borderRadius: BorderRadius.circular(5))),
keyboardType: TextInputType.number,
validator: (value) => value.isEmpty ? 'Number Phone cannot be empty!': null,
onChanged: (value) {
setState(() => phone = value);
},
),
SizedBox(height: 10.0),
TextFormField(
decoration: InputDecoration(
hintText: 'Unique ID ',
border: OutlineInputBorder(borderRadius: BorderRadius.circular(5))),
keyboardType: TextInputType.number,
validator: (value) => value.isEmpty ? 'Ic number cannot be empty!': null,
onChanged: (value) {
setState(() => uniqueID = value);
},
),
const SizedBox(height: 20.0),
RaisedButton(
color: Colors.redAccent,
textColor: Colors.black,
child: Text("Update"),
onPressed: () async {
if(_formKey.currentState.validate()){
_formKey.currentState.save();
} else {
print("Validator are correct!");
}
}
),
],
),
),
);
}
)
);
}
}

HomeSupervisor类

import 'package:flutter/material.dart';
import 'package:finalyearproject/model/NewUser.dart';
import 'package:finalyearproject/screen/crud/UpdateSupervisor.dart';
import 'package:finalyearproject/screen/crud/AddSupervisor.dart';
import 'package:finalyearproject/service/database.dart';
import 'package:finalyearproject/sidebar/AdminDrawer.dart';

class HomeSupervisor extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
backgroundColor: Colors.redAccent,
title: Text('Supervisor'),
actions: <Widget>[
IconButton(
icon: Icon(
Icons.add,
color: Colors.white,
),
onPressed: () {
Navigator.push(context,
MaterialPageRoute(builder: (context) => AddSupervisor()));
})
],
),
drawer: AdminDrawer(),
body: ListSupervisor(),
);
}
}
class ListSupervisor extends StatefulWidget {
@override
_ListSupervisorState createState() => _ListSupervisorState();
}
class _ListSupervisorState extends State<ListSupervisor> {
NewUser user;
@override
Widget build(BuildContext context) {
return Container(
child: FutureBuilder(
future: DatabaseService().getPost(),
builder: (_, snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return Center(
child: Text("Loading..."),
);
} else {
return ListView.builder(
itemCount: snapshot.data.length,
itemBuilder: (_, index) {
return Card(
child: ListTile(
title: Container(
alignment: Alignment.centerLeft,
child: Column(
children: <Widget>[
SizedBox(height: 5.0),
Container(alignment: Alignment.centerLeft,
child: Text(
snapshot.data[index].data["name"]),
),
SizedBox(height: 5.0),
Container(alignment: Alignment.centerLeft,
child: Text(
snapshot.data[index].data["email"]),
),
SizedBox(height: 5.0),
Container(alignment: Alignment.centerLeft,
child: Text(
snapshot.data[index].data["uniqueID"]),
),
],
),
),
trailing: Row(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
IconButton(
icon: Icon(Icons.delete),
color: Colors.red,
onPressed: (){
}
),
IconButton(
icon: Icon(Icons.edit),
color: Colors.black,
onPressed: () {
Navigator.push(context, MaterialPageRoute(builder: (context) => UpdateSupervisor()));  //here the line error show//
}
),
IconButton(
icon: Icon(Icons.share),
onPressed: () {
}
),
],
)
),
);
});
}
}),
);
}
}

然后erorr显示，在第96:101行中，我nagivator.push的Iconbutton到UpdateSupervisor。所以我的问题是如何将流提供程序包装在onPressed((中？

错误：在此UpdateSupervisor Widget 上找不到正确的提供程序

要修复，请：

• 确保提供程序是此UpdateSupervisor小部件的祖先
• 向提供程序提供类型
• 向消费者提供类型
• 为Provider.of((提供类型
• 始终使用包导入。例如："import"包：my_app/my_code.dart'
• 确保使用正确的context

如果这些解决方案都不起作用，请在以下位置提交错误：https://github.com/rrousselGit/provider/issues相关的导致错误的小部件是：UpdateSupervisorfile:///D:/Android_project/finalyearproject/lib/screen/home/HomeSupervisor.dart:96:101

Answer 1

用这样的提供者包装MaterialApp。

ChangeNotifierProvider<NewUser>(create: (context) => NewUser(),
child: MaterialApp(
title: 'Flutter Demo',
home:Home(),
),
);

此外：我使用ChangeNotificationerProvider，因为我认为您的提供商正在扩展ChangeNotifier。

如果您没有扩展ChangeNotifier您可以使用以下基本形式的提供商：

Provider<NewUser>(
create: (context) => NewUser(),
child: child: MaterialApp(
title: 'Flutter Demo',
home:Home(),
),
)

这将使您能够使用NewUser对象作为所有提供者派生类的依赖注入，如

class HomeWidget extends StatelessWidget {
@override
Widget buid(BuildContext context){
final provider = Provider.of<NewUser>(contextm, listen:false); /// you can to not set listen on false it does not matter in this case cause this type of provider is just an injection
return Text(provider.someText);
}
}

还有StreamProvider，让您可以监听流并更新Widget，当流接收数据时，它会注入此提供程序，也可以查看它。

还有一个MultiProvider，它可以让您用多个提供商包装MaterialApp。

也检查这个网址太

flatter.dev 中多供应商的示例

void main() {
runApp(
MultiProvider(
providers: [
ChangeNotifierProvider(create: (context) => CartModel()),
Provider(create: (context) => SomeOtherClass()),
],
child: MyApp(),
),
);
}