ChangeNotifierProvider dosen't create new ChangeNotifier instance

Question

我有一个平板电脑的大纲详细信息页面。
我想在列表中选择项目时更改详细信息页面。
所以我写了这样的代码，

class AttendancesModel with ChangeNotifier {
final int userId;
AttendancesModel(this.userId);
List<Attendance> attendances = [];
// do initialize
}
class AttendancesPage extends StatelessWidget {
final int userId;
AttendancesPage(this.userId);
@override
Widget build(BuildContext context) {
return ChangeNotifierProvider(
create: (_) => AttendancesModel(userId),
child: Consumer(
builder: (_, model, __) {
print('model.userId=${model.userId}')
return Scaffold(
// appbar, body, etc...
);
}
)
);
}
}

但是，构建器收到的模型始终是相同的值。
因此，更改用户选择不会更改详细信息屏幕。
如何创建新模型？

谢谢。

[编辑] 像这样的用户列表页面将通知用户选择

class UserListModel with ChangeNotifier {
List<User> users = [];
int _selectedUserId;
int get selectedUserId => _selectedUserId;
set selectedUserId(int userId) {
_selectedUserId = userId;
notifyListeners();
}
}
class UserListPage extends StatelessWidget {
Widget build(BuildContext context) {
return ChangeNotifierProvider.value(
value: Provider.of<UserListModel>(context),
child: Consumer(
builder: (_, model, __) {
return ListView.builder(
itemBuilder: (_, i) {
final user = model.users[i];
return ListTile(
title: Text(user.name),
onTap: () => model.selectedUserId = user.id,
);
},
itemCount: model.users.length
);
}
)
)
}
}
class HomePage extends StatelessWidget {
Widget build(BuildContext context) {
return ChangeNotifierProvider(
create: (_) => UserListModel(),
child: HomePageBody()
);
}
}
class HomePageBody extends StatelessWidget {
Widget build(BuildContext context) {
return Scaffold(
body: Row(
children: <Widget>[
SizedBox(width: 320, child: UserListPage()),
ChangeNotifierProvider.value(
value: Provider.of<UserListModel>(context),
child: Consumer<UserListModel>(
builder: (_, model, __) {
return AttendancePage(model.selectedUserId);
}
)
)
]
)
)
}
}

Answer 1

在 AttendancesPage 中，您始终传递相同的 userID。 只是为了理解，您想在 AttendanceModel 上打印一些与用户 ID 相关的信息，对吗？

我做了这个。让我们看看它是否有用。

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 MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: HomePage(),
);
}
}
class User {
final int userId;
final String name;
User(this.userId, this.name);
}
class Attendance {
final int attendanceId;
final int userId;
final String data;
Attendance({
this.attendanceId,
this.data,
this.userId,
});
}
class UserListModel with ChangeNotifier {
List<User> users = [
User(15, "Rick"),
User(14, "Bob"),
User(12, "Lola"),
];
int _selectedUserId;
int get selectedUserId => _selectedUserId;
void changeSelectedUserId(int userId) {
_selectedUserId = userId;
print(_selectedUserId);
notifyListeners();
}
}
class UserListPage extends StatelessWidget {
Widget build(BuildContext context) {
return Consumer<UserListModel>(
builder: (_, model, __) {
return ListView.builder(
itemBuilder: (_, i) {
final user = model.users[i];
return ListTile(
title: Text(user.name),
onTap: () => model.changeSelectedUserId(user.userId),
);
},
itemCount: model.users.length);
},
);
}
}
class HomePage extends StatelessWidget {
Widget build(BuildContext context) {
return ChangeNotifierProvider(
create: (_) => UserListModel(),
child: HomePageBody(),
);
}
}
class HomePageBody extends StatelessWidget {
Widget build(BuildContext context) {
return Scaffold(
body: Row(
children: <Widget>[
Expanded(child: UserListPage()),
Consumer<UserListModel>(
builder: (_, model, __) {
return Expanded(
child: ChangeNotifierProvider(
create: (_) => AttendancesModel(),
child: AttendancesPage(model.selectedUserId),
),
);
},
),
],
),
);
}
}
class AttendancesModel with ChangeNotifier {
List<Attendance> attendances = [
Attendance(attendanceId: 1, userId: 12, data: "Attendance1"),
Attendance(attendanceId: 2, userId: 15, data: "Attendance2"),
Attendance(attendanceId: 3, userId: 14, data: "Attendance3"),
];
Attendance findByUserId(int userId) {
return attendances.firstWhere((element) => element.userId == userId);
}
}
class AttendancesPage extends StatelessWidget {
final int userId;
AttendancesPage(this.userId);
@override
Widget build(BuildContext context) {
final attendance =
Provider.of<AttendancesModel>(context).findByUserId(userId);
return Scaffold(
body: Center(
child: Text(
"${attendance.attendanceId} - ${attendance.userId} - ${attendance.data}"),
),
);
}
}