firebase - 我正在尝试使用 Provider 和 Firebase 流式传输模型列表，并将字段值设置为我应用程序中的另一个模型

Question

我正在使用 Flutter、Provider 和 Firebase 构建一个生产力应用程序。我目前有许多流，我从 Firestore 中收集这些流并将它们转换为模型列表。我遇到了一个问题，当我尝试创建任务模型列表时，我返回了一个空列表。在 Firestore 中，我有一个任务、状态和项目的集合。我想将 task.project 值设置为等于项目集合中关联的 Project 模型。主 Dart :

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(ProductivityApp());
}

class ProductivityApp extends StatefulWidget {
  @override
  _ProductivityAppState createState() => _ProductivityAppState();
}

class _ProductivityAppState extends State<ProductivityApp> {
  bool _initialized = false;
  bool _error = false;

  void initializeFlutterFire() async {
    try {
      await Firebase.initializeApp();
      setState(() {
        _initialized = true;
      });
    } catch (e) {
      _error = true;
    }
  }

  @override
  void initState() {
    initializeFlutterFire();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    if (_error) {
      return Center(child: Text('Something went wrong'));
    }
    if (!_initialized) {
      return Center(child: Text('Loading'));
    }
    return StreamProvider<User>.value(
      value: AuthService().user,
      child: MultiProvider(   // TODO: fix the issue for user to be logged in for the first time
        providers: [
          StreamProvider<List<Project>>.value(value: ProjectService().streamProjects()),
          StreamProvider<List<Task>>.value(value: TaskService().streamTasks(context)),
          StreamProvider<List<Status>>.value(value: StatusService().streamStatuses())
        ],
          child: MaterialApp(
            title: 'ProductivityApp',
            theme: appTheme(),
            // home: Wrapper(),
            // routes: routes,
            onGenerateRoute: generateRoute,
            initialRoute: '/',
          ),
      ),

    );
  }
}

任务流:

// Snapshot Conversion to Task Model and Stream
  Stream<List<Task>> streamTasks(BuildContext context) {
    var ref = _getTaskReference();
    return ref.snapshots().map((querySnapshot) => querySnapshot.docs
        .map((queryDocument) => Task.fromFirestore(queryDocument, context))
        .toList());
  }

任务模型:

class Task {
  String taskID = '';
  String taskName = 'Default Name';
  Project project = Project();
  Status status = Status();
  int taskTime = 0;
  DateTime dueDate = DateTime(1);
  DateTime createDate = DateTime.now();
  // List<String> subtasks = [];

  Task(
      {this.taskID,
      this.taskName,
      this.project,
      this.status,
      this.taskTime,
      this.dueDate,
      this.createDate});



  factory Task.fromFirestore(DocumentSnapshot snapshot, BuildContext context) {
    List<Project> projects = Provider.of<List<Project>>(context);
    List<Status> statuses = Provider.of<List<Status>>(context);
    Map data = snapshot.data();
    Project associatedProject = projects
        .firstWhere((project) => project.projectName == data['pojectName']);
    print(associatedProject);
    Status status = statuses
        .firstWhere((status) => status.statusName == data['statusName']);
    return Task(
        taskID: snapshot.id ?? '',
        taskName: data['taskName'].toString() ?? '',
        project: associatedProject ?? Project(),
        status: status ?? Status(),
        taskTime: data['taskTime'] ?? 0,
        dueDate:
            DateTimeFunctions().timeStampToDateTime(date: data['dueDate']) ??
                DateTime.now(),
        createDate:
            DateTimeFunctions().timeStampToDateTime(date: data['createDate']) ??
                DateTime.now());
  }
}

感谢您的帮助!

Answer 1

我终于找到了解决问题的方法!我使用了许多不同的资源并将它们组合在一起以获得一个工作模型。

首先，我实现了一个基于此 answer 的用户信息重建的 Auth_widget_builder .这实际上解决了先前留待稍后修复的问题。通过使用这种方法，我能够根据用户重建 Material Design 之上的身份验证小部件，我需要访问我的用户集合中正确的 firestore 文档。

主.dart

@override
  Widget build(BuildContext context) {
    if (_error) {
      return Center(child: Text('Something went wrong'));
    }
    if (!_initialized) {
      return Center(child: Text('Loading'));
    }
    return Provider(
      create: (context) => AuthService(),
      child: AuthWidgetBuilder(builder: (context, userSnapshot) {
        return MaterialApp(
          title: 'Productivity App',
          theme: appTheme(),
          home: AuthWidget(userSnapshot: userSnapshot),
          // onGenerateRoute: generateRoute,
          // initialRoute: '/',
        );
      }),
    );
  }
}

其次，在 Auth_widget_builder 中我嵌套了两个 MultiProvider。第一个创建的提供者将产生我的服务类。然后我添加了 builder: function based on this answer ，它返回了第二个包含我的 StreamProvider 的 MultiProvider。这是可行的，因为 builder: 函数重建了 BuildContext，这样我就可以访问其他 Provider 中的对象以保存为另一个对象中的字段。

auth_widget_builder.dart

/// Used to create user-dependant objects that need to be accessible by all widgets.
/// This widget should live above the [MaterialApp].
/// See [AuthWidget], a descendant widget that consumes the snapshot generated by this builder.

class AuthWidgetBuilder extends StatelessWidget {
  const AuthWidgetBuilder({Key key, @required this.builder}) : super(key: key);
  final Widget Function(BuildContext, AsyncSnapshot<UserModel>) builder;

  @override
  Widget build(BuildContext context) {
    print('AuthWidgetBuilder rebuild');
    final authService = Provider.of<AuthService>(context, listen: false);
    return StreamBuilder<UserModel>(
      stream: authService.onAuthStateChanged,
      builder: (context, snapshot) {
        print('StreamBuilder: ${snapshot.connectionState}');
        final UserModel user = snapshot.data;
        if (user != null) {
          return MultiProvider(
            providers: [
              Provider<UserModel>.value(value: user),
              Provider(create: (context) => ProjectService()),
              Provider(create: (context) => StatusService()),
              Provider(create: (context) => TaskService()),
              Provider(create: (context) => TimeService()),
            ],
            builder: (context, child) {
              return MultiProvider(
                providers: [
                  StreamProvider<List<Project>>.value(
                      value: Provider.of<ProjectService>(context)
                          .streamProjects()),
                  StreamProvider<List<Status>>.value(
                      value: Provider.of<StatusService>(context)
                          .streamStatuses()),
                  StreamProvider<List<Task>>.value(
                      value: Provider.of<TaskService>(context)
                          .streamTasks(context)),
                  StreamProvider<List<TimeEntry>>.value(
                      value: Provider.of<TimeService>(context)
                          .streamTimeEntries(context))
                ],
                child: builder(context, snapshot),
              );
            },
            child: builder(context, snapshot),
          );
        }
        return builder(context, snapshot);
      },
    );
  }
}

第三，我更新了服务类以查找适当的对象并将其传递给模型。

tasks_data.dart

// Snapshot Conversion to Task Model and Stream
  Stream<List<Task>> streamTasks(BuildContext context) {
    CollectionReference ref = _getTaskReference();
    List<Project> projects;
    getProjects(context).then((projectList) => projects = projectList);
    List<Status> statuses;
    getStatuses(context).then((statusList) => statuses = statusList);
    return ref.snapshots().map((QuerySnapshot querySnapshot) =>
        querySnapshot.docs.map((QueryDocumentSnapshot queryDocument) {
          Project project = projects[projects.indexWhere((project) =>
              project.projectName ==
              queryDocument.data()['projectName'].toString())];
          Status status = statuses[statuses.indexWhere((status) =>
              status.statusName == queryDocument.data()['status'].toString())];
          return Task.fromFirestore(queryDocument, project, status);
        }).toList());
  }

  Future<List<Project>> getProjects(BuildContext context) async {
    List<Project> projects =
        await Provider.of<ProjectService>(context).streamProjects().first;
    return projects;
  }

  Future<List<Status>> getStatuses(BuildContext context) async {
    List<Status> statuses =
        await Provider.of<StatusService>(context).streamStatuses().first;
    return statuses;
  }

关于此实现的最好的部分是它全部发生在 Material Widget 之上，这意味着我可以使用正常范围之外的小部件(如 Navigator.push())访问它。希望这适用于任何需要类似解决方案的人。