flutter - `Future` 不是类型 `Stream` 的子类型

Question

我制作了简单的单例类以在 flutter 上使用 StreamBuilder小部件，例如:

StreamBuilder<User>(
  stream: MydbModel.create().then((dao) => dao.getUserStream()) as Stream<User>,
  builder: (_, snapshot) {
    ...
  },
)

在那个

MydbModel.create().then((dao) => dao.getUserStream())

返回Future<Stream<User>>我的类型转换不工作只有 Stream<User> .

错误:

> type 'Future<Stream<User>>' is not a subtype of type 'Stream<User>' in type cast

我该如何解决这个问题？

我完成的类(class):

class MydbModel{
  UserDao _userDao;

  MydbModel._(this._userDao);
  static Future<MydbModel> create() async => MydbModel._(await initialDatabase());

  static Future<UserDao> initialDatabase() async {
    var db = await $FloorAppDatabase.databaseBuilder('flutter_database.db').build();
    return db.userDao;
  }

  Stream<User> getUserStream(){
    return userDao.getUserInfo();
  }

  UserDao get userDao=>_userDao;
}

Answer 1

你需要先等待Future:

FutureBuilder(
  future: MydbModel.create(),
  builder: (BuildContext context, AsyncSnapshot<MydbModel> snapshot) {
    if (!snapshot.hasData) return Container();
    return StreamBuilder(
      stream: snapshot.data.getUserStream(),
      builder: ..,
    );
  },
);

我使用 FutureBuilder 来等待 Future 并在加载 future 时创建 StreamBuilder。