Firebase如何从数据库正确检索数据并显示数据

Question

我正在尝试从Firebase中提取数据并显示用户的名称和状态。 我目前遇到空值异常。

public class ProfileFragment extends Fragment {

private DatabaseReference mUserDatabase;
private FirebaseUser mCurrentUser;

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view =  inflater.inflate(R.layout.fragment_profile, container, false);

    CircleImageView displayProfilePicture = view.findViewById(R.id.settings_profile_picture);
    final TextView mName = view.findViewById(R.id.settings_user_name);
    final TextView mStatus = view.findViewById(R.id.settings_user_status);

    mCurrentUser = FirebaseAuth.getInstance().getCurrentUser();

    String current_uid = Objects.requireNonNull(mCurrentUser).getUid();

    mUserDatabase = FirebaseDatabase.getInstance().getReference().child("Users").child(current_uid);

    mUserDatabase.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

            String name = (Objects.requireNonNull(dataSnapshot.child("name").getValue())).toString();
            String status = Objects.requireNonNull(dataSnapshot.child("status").getValue()).toString();
            String image = Objects.requireNonNull(dataSnapshot.child("image").getValue()).toString();
            String thumb_image = Objects.requireNonNull(dataSnapshot.child("thumb image ").getValue()).toString();

            mName.setText(name);
            mStatus.setText(status);

        }

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

        }


    });
    return view;
}}

我也尝试过使用此代码以其他方式实现此功能，但是我仍然无法显示数据。

public class ProfileFragment extends Fragment {

private DatabaseReference mUserDatabase;
private FirebaseUser mCurrentUser;

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view =  inflater.inflate(R.layout.fragment_profile, container, false);

    CircleImageView displayProfilePicture = view.findViewById(R.id.settings_profile_picture);
    final TextView mName = view.findViewById(R.id.settings_user_name);
    final TextView mStatus = view.findViewById(R.id.settings_user_status);

    mCurrentUser = FirebaseAuth.getInstance().getCurrentUser();

    String current_uid = Objects.requireNonNull(mCurrentUser).getUid();

    mUserDatabase = FirebaseDatabase.getInstance().getReference().child("Users").child(current_uid);

    mUserDatabase.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            for(DataSnapshot datas: dataSnapshot.getChildren()){
                String keys=datas.getKey();
                String displayname=datas.child("name").getValue().toString();

                mName.setText(displayname);
        }}

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

        }


    });
    return view;
}}

我的数据库结构如下：

Answer 1

由于您已经具有userId因此您无需循环即可访问直接子级。

请尝试以下操作：

 mUserDatabase = FirebaseDatabase.getInstance().getReference().child("Users").child(current_uid);

mUserDatabase.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            String keys=dataSnapshot.getKey();
            String displayname=dataSnapshot.child("name").getValue().toString();

            mName.setText(displayname);
    }}

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

    }  
 });