Flutter:在应用程序初始化时将Firestore数据加载到提供程序中

Question

我正在做一个有Firestore db后端的应用程序，因为我不需要从应用程序中更新任何东西，而且数据是相当静态的，我想在应用程序初始化时将所有Firestore数据反序列化为Dart数据结构(理想情况下是反序列化到提供者中)，以避免在我的Widget类中到处都是Future/StreamBuilder。

Firestore中的数据结构如下

Route
|->Room
   |->Point of Interest

这是Provider类

class AppData with ChangeNotifier {
  static final FirebaseRepo _repo = new FirebaseRepo();

  List<model.Route> _routes;

  List<model.Route> get routes => _routes;

  set routes(List<model.Route> routes) {
    _routes = routes;
    notifyListeners();
  }

  AppData() {
    _loadData();
  }

  Future<void> _loadData() async {
    routes = await _repo.findAllRoutes();
  }

  // some get methods that operate on _routes
}

这是我加载routes的repository类的摘录

class FirebaseRepo {
  FirebaseFirestore _db = FirebaseFirestore.instance;
  Source _dbSource = Source.cache;

  Future<List<model.Route>> findAllRoutes() async {
    List<model.Route> routes = [];
    var routeContent = await _db.collection('content')
        .where("type", isEqualTo: "route")
        .orderBy("order", descending: false)
        .get(GetOptions(source: _dbSource));

    if (routeContent.docs.length > 0) {
      await Future.forEach(routeContent.docs, (snapshot) async {
        model.Route route = await loadRouteFromSnapshot(snapshot);
        route.rooms = await findRouteRooms(route.id);
        routes.add(route);
      });
    }

    return routes;
  }

  Future<List<Room>> findRouteRooms(String routeId) async {
    List<Room> rooms = [];
    var roomContent = await _db.collection('content')
        .doc(routeId)
        .collection("rooms")
        .orderBy("order", descending: false)
        .get(GetOptions(source: _dbSource));

    if (roomContent.docs.length > 0) {
      await Future.forEach(roomContent.docs, (snapshot) async {
        Room room = await loadRoomFromSnapshot(snapshot, routeId);
        room.pois = await findRoomPois(room.parentRouteId, room.id);
        rooms.add(room);
      });
    }

    return rooms;
  }

  Future<List<Poi>> findRoomPois(String routeId, String roomId) async {
    List<Poi> pois = [];
    var poiContent = await _db.collection('content')
        .doc(routeId)
        .collection("rooms")
        .doc(roomId)
        .collection("poi")
        .orderBy("order", descending: false)
        .get(GetOptions(source: _dbSource));

    if (poiContent.docs.length > 0) {
      await Future.forEach(poiContent.docs, (snapshot) async {
        Poi poi = await loadPoiFromSnapshot(snapshot, routeId, roomId);
        pois.add(poi);
      });
    }

    return pois;
  }

................
}

这是主类

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(CatedralApp());
}

class App extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        brightness: Brightness.light,
        primaryColor: Colors.white,
        fontFamily: 'Alata',
      ),
      routes: {
        RouteDetail.routeName: (context) => RouteDetail(),
        RoomDetail.routeName: (context) => RoomDetail(),
        PoiDetail.routeName: (context) => PoiDetail(),
      },
      home: LoadingScreen()
    );
  }
}

class LoadingScreen extends StatelessWidget{
  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider.value(
      value: AppData(),
      child: Consumer<AppData> (
        builder: (BuildContext context, AppData provider, Widget child) {
          if (provider.routes != null) {
            return Home();
          } else {
            return Stack(
              children: <Widget>[
                Container(
                  alignment: Alignment.center,
                  color: Colors.white,
                  child: Image.asset('assets/img/splash_background.png'),
                ),
                Container(
                  alignment: Alignment(0.0, 0.0),
                  child: Image.asset(
                    'assets/img/icon.png',
                    height: 200,
                    width: 200,
                  ),
                )
              ],
            );
          }
        }
      )
    );
  }
}

这个想法是在数据加载时显示闪屏，然后转到Home视图，我尝试了上面代码的一些变体，但似乎不起作用，提供者中的数据总是一个空列表，老实说，我甚至不知道我想要做的是不是对于Flutter应用程序应该如何工作是“正确的”，但我正在尽可能多地了解……

据我测试，从缓存中读取数据并不是问题，因为它会尝试缓存，然后移动到Source.server (但我用Source.server尝试过，但无论如何都不能工作)，当已经有缓存的数据时，应用程序工作得很好，并且在没有缓存数据的情况下进行调试，存储库方法实际上是从Firestore中检索数据，所以与数据库的连接也是很好的。

Answer 1

好吧，事实证明我从缓存中读取是错误的，正确的方法是(显然，如果你总是想要强制从缓存中读取)

Future<List<model.Route>> findAllRoutes() async {
    List<model.Route> routes = [];
    var routeContent = await _db.collection('content')
        .where("type", isEqualTo: "route")
        .orderBy("order", descending: false)
        .get(GetOptions(source: Source.Cache));

    if (routeContent.docs.length > 0) {
      ...
    } else {
      routeContent = await _db.collection('content')
        .where("type", isEqualTo: "route")
        .orderBy("order", descending: false)
        .get(GetOptions(source: Source.Server));
      ...
    }

    return routes;
  }

这个方法尝试从缓存中读取，然后从服务器读取，所以在第一个应用程序运行时，它将从服务器读取，然后在随后的运行中，它将始终从缓存中读取，我希望这能对某些人有所帮助:)不管怎样，如果您对整个解决方案有一些观察，将非常感谢！