MultiProvider 在子部件中发送 NULL 但在控制台中打印正确的值

Question

我的主页提供商已初始化：

Widget build(BuildContext context) {
    return SafeArea(
      child: MultiProvider(
        providers: [
          ChangeNotifierProvider<EmailAuth>(create: (context) => EmailAuth()),
        ],
        child: Scaffold(
          resizeToAvoidBottomInset: true,
          floatingActionButton: FloatingActionButton(.....

用户登录时触发的我的身份验证功能 (Firebase)

class EmailAuth extends ChangeNotifier {
  final _auth = FirebaseAuth.instance;
  final dbRef = FirebaseFirestore.instance.collection("users");
  String userid;
 
  Future signIn({String email, String password}) async {
    final currentUser = await _auth.signInWithEmailAndPassword(
        email: email, password: password);
    if (currentUser != null) {
      userid = _auth.currentUser.uid;
      dbRef.doc(_auth.currentUser.uid).update({
        "lastLogin": DateTime.now(),
      });
    } else {
      print("something didn't work");
    }
    print(userid);
    notifyListeners();
    return userid;
  }
  }

这是我的消费者在主页 - AppBar 中的设置方式

 title: Consumer<EmailAuth>(
                    builder: (context, data, child) => Text(
                      "${data.userid}",
                      style: TextStyle(color: Colors.indigoAccent),
                    ),
                  ),

但是 AppBar 上的输出是 NULL。我做错了什么？！

我一直以此作为实现的参考： https://medium.com/flutter-community/making-sense-all-of-those-flutter-providers-e842e18f45dd

Answer 1

旧版提供程序包中存在类似的已知错误。请更新到最新版本并检查问题是否仍然存在。然而，

MultiProvider 应该是这样的：

@override
  Widget build(BuildContext context) {
    return MultiProvider( //                                     <--- MultiProvider
      providers: [
        ChangeNotifierProvider<MyModel>(create: (context) => MyModel()),
        ChangeNotifierProvider<AnotherModel>(create: (context) => AnotherModel()),
      ],

应该这样吃

child: Consumer<MyModel>( //            <--- MyModel Consumer
                        builder: (context, myModel, child) {
                          return RaisedButton(
                            child: Text('Do something'),
                            onPressed: (){
                              // We have access to the model.
                              myModel.doSomething();
                            },
                          );
                        },
                      )


class MyModel with ChangeNotifier { //                        <--- MyModel
  String someValue = 'Hello';
  void doSomething() {
    someValue = 'Goodbye';
    print(someValue);
    notifyListeners();
  }

}

MultiProvider 在子部件中发送 NULL 但在控制台中打印正确的值

MultiProvider sending NULL in child widgets but prints right value in Console

dart

flutter

flutter-provider