Question

因此，我试图显示与已登录用户有关的数据，但与之相关的数据却使我返回null我尝试了多种解决方案，但没有用

public class HomeViewModel extends ViewModel {

private MutableLiveData<String> mText;
DatabaseReference userdata;
String namedata;

public HomeViewModel() {
    userdata = FirebaseDatabase.getInstance().getReference();

    userdata.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            for(DataSnapshot snap : dataSnapshot.getChildren()){
                User user = snap.getValue(User.class);
                namedata = user.getUserId();

            }
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });
    mText = new MutableLiveData<>();
    mText.setValue("Welcome back! " +namedata);
}

public LiveData<String> getText() {
    return mText;
}}`

这是我想要获取这些数据并将其显示在视图中的User.class

public class User {
String userId;
String userPhone;
String userGender;

public User() {

}

public User(String userId, String userPhone, String userGender) {
    this.userId = userId;
    this.userPhone = userPhone;
    this.userGender = userGender;
}



public String getUserId() {
    return userId;
}

public String getUserPhone() {
    return userPhone;
}

public String getUserGender() {
    return userGender;
}}

Answer 1

您必须调用“ userId”

@Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                for (DataSnapshot snap : dataSnapshot.getChildren()){
                    HashMap<String, String> map = (HashMap<String, String>) snap.getValue();
                    if (map.containsKey("userId")) {
                        if (map.get("userId").equals("william henry")) {
                            String userGender = map.get("userGender");
                        }
                    }
                }
            }

或

@Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                for (DataSnapshot snap : dataSnapshot.getChildren()){
                    HashMap<String, String> map = (HashMap<String, String>) snap.getValue();
                    if (map.containsKey("userId")) {
                        String userGender = map.get("userId");
                    }
                }
            }

Answer 2

第一个FirebaseDatabase.getInstance().getReference()指向您的根目录（这是数据库上方的链接）。因此，您需要指向您想要获得的内容（即用户树）。其次，您必须将数据设置在onDataChange内，因为它不具有同步功能（这意味着您的姓名数据始终不遵循从onDataChange返回的数据）

 FirebaseDatabase.getInstance().getReference().child("User").orderByChild("userId").equalTo(*your_logged_in_user_id*).addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        Iterator iterator = dataSnapshot.getChildren().iterator()
        if(iterator.hasNext()){
            User user = iterator.next().getValue(User.class)
            }
                name = user.getName();
            }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });

Answer 3

由于没有从正确的节点获取值，因此您将获得null。有用户子级，您想获取用户子级的值。

userdata = FirebaseDatabase.getInstance().getReference().child("User");
userdata.addOnChildEventListener( new ChildEventListener() {

                @Override
                public void onChildAdded(DataSnapshot snap, String previousChildName) {
                //get value here.
                  User user = snap.getValue(User.class);
                }

                @Override
                public void onChildChanged(DataSnapshot dataSnapshot, String previousChildName) {

                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {

                }

                @Override
                public void onChildMoved(DataSnapshot dataSnapshot, String previousChildName) {

                }

                @Override
                public void onCancelled(DatabaseError error) {
                }
            });

您想获取单个用户数据，然后 userdata = FirebaseDatabase.getInstance（）。getReference（）。child（“ User”）。child（userIdOfthatuser）;

userdata.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot snap) {

                User user = snap.getValue(User.class);
                namedata = user.getUserId();


        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });

如何从Firebase实时数据库中检索数据并将其显示在配置文件仪表板中

3 个答案: