firebase - flutter/火力基地 : How can i access the current user without using '.then(...)' function

Question

我试图避免在我需要访问当前用户 UID 的所有代码中使用 .then((u) { return u.uid }) 函数，而只是通过调用getCurrentUser().uid 以获得更快的访问速度。但是，它给了我一个错误 The getter 'uid' was called on null. 但它不是 null，因为它确实在控制台中打印，但只有在显示它为 null 并且最后出现一些错误之后原因。我不太了解 Future/Async/Await 逻辑，因此非常感谢任何帮助!

class UsersAPI {
  final DatabaseReference usersRef = FirebaseDatabase.instance.reference().child(Config.users);

  Future<FirebaseUser> currentUser() async {
    return await FirebaseAuth.instance.currentUser();
  }

  FirebaseUser getCurrentUser() {
    FirebaseUser user;

    this.currentUser().then((u) {
      user = u;
      print('USER 1 $user'); // Prints after 'USER 2'
    });

    print('USER 2 $user'); // Prints first

    if (user != null) {
      return user;
    } else {
      return null;
    }
  }

  DatabaseReference getCurrentUserRef() {
    return this.usersRef.child(this.getCurrentUser().uid); // GIVES THE 'uid' WAS CALLED ON NULL ERROR
  }

  observeCurrentUser(Function onSuccess(User u)) {
    this.usersRef.child(this.getCurrentUser().uid).onValue.listen( (event) { // GIVES THE 'uid' WAS CALLED ON NULL ERROR
      DataSnapshot snapshot = event.snapshot;

      if (snapshot.value != null) {
        User user = User().transform(snapshot.key, snapshot.value);
        onSuccess(user);
      }
    });
  }

  observeUser(String userID, Function onSuccess(User u), Function onFailure(String e)) {
    this.usersRef.child(userID).onValue.listen( (e) {
      DataSnapshot snapshot = e.snapshot;
      if (snapshot.value != null) {
        User user = User().transform(snapshot.key, snapshot.value);
        onSuccess(user);
      } else {
        onFailure("User Not Found...");
      }
    });
  }
}

示例用法 - WORKS:

APIs().usersAPI.currentUser().then((u) {
  APIs().usersAPI.observeUser(u.uid, (u) {
    onSuccess(u);
  }, (e) {
    print(e);
  });
});

不起作用:

APIs().usersAPI.observeCurrentUser((u) {
  onSuccess(u);
});

Answer 1

  DatabaseReference getCurrentUserRef() async {
    return this.usersRef.child((await this.getCurrentUser()).uid); =
  }

比调用

var ref = await getCurrentUserRef()

漂亮一点

  DatabaseReference getCurrentUserRef() async {
    var firebaseUser = await this.getCurrentUser();
    return this.usersRef.child(firebaseUser.uid); 
  }

编辑:澄清一些关于异步的问题

您现在如何调用此函数来获取引用？

假设你想更新用户的数据，你可以这样做

Firestore.instance.runTransaction((transaction) async {
  var reference = await getCurrentUserRef();
  await transaction.set(reference, someData);
  });

或者你想从那个引用中读取数据

readAndProcessData() async {
  var reference = await getCurrentUserRef();
  DocumentSnapshot user = await reference.get();
  print(user.data.toString);
}