错误：在此 UpdateSupervisor 小部件上方找不到正确的 Provider<NewUser>

Question

如何将流提供程序包装在 onPressed 函数中？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: () {

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

然后错误显示，在第 96:101 行中，我将 nagivator.push 到 UpdateSupervisor 的 Iconbutton。 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 小部件上方找不到正确的提供程序

要修复，请：

• 确保 Provider 是此 UpdateSupervisor 小部件的祖先
• 向 Provider 提供类型
• 向消费者提供类型
• 向 Provider.of() 提供类型
• 始终使用包导入。例如：`import 'package:my_app/my_code.dart';
• 确保使用了正确的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： UpdateSupervisor file:///D:/Android_project/finalyearproject/lib/screen/home/HomeSupervisor.dart:96:101

Answer 1

像这样用提供者包装 MaterialApp。

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

另外： 我正在使用 ChangeNotifierProvider，因为我假设您的提供程序正在扩展 ChangeNotifier。

如果您不扩展 ChangeNotifier 您可以使用以下基本形式的提供程序：

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

这将使您可以使用 NewUser 对象作为所有 Provider 后代类的依赖注入，如下所示：

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 可以让您在流中收听并更新注入此提供程序的 Widget流将接收数据，也请检查一下。

还有一个 MultiProvider，它可以让您用多个 Provider 包装 MaterialApp。

也检查一下这个url

来自flutter.dev的MultiProvider示例

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