java - 如何从 firebase 实时数据库检索数据并将其显示在个人资料仪表板中

Question

所以我试图显示与已登录用户相关的数据，但与之相关的数据返回 null 我尝试了多种解决方案，但没有成功

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 View 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");
                    }
                }
            }