Flutter FutureBuilder 与 Firestore

Question

我正在尝试在颤振中创建一个列表，为每个单元格从 firestore 异步加载数据：

Future getUserDetails(String userID) async {
    DatabaseService databaseService =
        DatabaseService(currentUserId: _currentUserID);
    return databaseService.getUserDetails(userID: userID);
  }

Future sampleText() async {
    return Future.delayed(Duration(seconds: 3)).then((value) => randomString(5));
}

FutureBuilder _userAsyncCell(ClassAttendee attendeeData) {
    return FutureBuilder(
        future: getUserDetails(attendeeData.userId),//sampleText(),
        builder: (BuildContext context, AsyncSnapshot snapshot) {
          if (snapshot.connectionState == ConnectionState.waiting)
            return Center(child: CircularProgressIndicator());
          else if (snapshot.hasData)
            return Text("DATA: ${snapshot.data}");
          else if (snapshot.hasError)
            return Text("ERROR: ${snapshot.error}");
          else
            return Text('None');
        });
  }

数据库服务中的AND：

final CollectionReference _usersCollection =
      Firestore.instance.collection('users');

Future<User> getUserDetails({String userID}) async {
    print('Fetching User public data ${userID}');
    _usersCollection.document(userID).get().then((userJSON) {
      User user = User.fromJson(userJSON.data);
      print("Received user info: ${user.identifier}");
      return user;
    });
  }

问题是futureBuilder中接收到的数据总是nil。

当使用sampleText() 而不是getUserDetails() 时，它工作正常。

你知道为什么会这样吗？

编辑： 在日志中我可以看到，userDetails 正确地返回了值，futureBuilder 的构建器被调用：

flutter: Fetching User public data Rh8snwoI27V6pA3wkmQwBPitgl63
flutter: Received user info: Rh8snwoI27V6pA3wkmQwBPitgl63

Answer 1

尝试如下重构您的代码。

您没有等待响应，因此未来返回 nil 值

Future<User> getUserDetails({String userID}) async {
    print('Fetching User public data ${userID}');
    await _usersCollection.document(userID).get().then((userJSON) {
      User user = User.fromJson(userJSON.data);
      print("Received user info: ${user.identifier}");
      return user;
    });
}