如何在Firebase Recycler适配器中获取用户ID，并得到错误无法为child（）中的参数'pathString'传递null

Question

我正在尝试在Firebase Recycler Adapter中获取userId，并使用ViewHolder和UserProfile来获取用户名，状态，userID等。但是，当尝试获取用户ID并传递到另一个片段时，出现“无法在child（）中为参数'pathString'传递空值”

这是我在SearchFragment和UserDetailFragment中的代码

 public void firebaseSearch(String searchText){
        Query firebaseSearchQuery = reference.orderByChild("username").startAt(searchText).endAt(searchText + "\uf8ff");
        DatabaseReference userDetail = FirebaseDatabase.getInstance().getReference("User");

        FirebaseRecyclerAdapter<UserProfile, ViewHolder> recyclerAdapter =
                new FirebaseRecyclerAdapter<UserProfile, ViewHolder>(
                        UserProfile.class,
                        R.layout.user_search_list,
                        ViewHolder.class,
                        firebaseSearchQuery
                ) {
                    @Override
                    protected void populateViewHolder(ViewHolder viewHolder, final UserProfile userProfile, final int i) {
                        viewHolder.setDetails(userProfile.getUsername(), userProfile.getUsername());

                        viewHolder.itemView.setOnClickListener(new View.OnClickListener() {
                            @Override
                            public void onClick(View v) {
                                Bundle bundle = new Bundle();
                                bundle.putString("username", userProfile.getUsername());
                                bundle.putString("display_name", userProfile.getDisplay_name());
                                bundle.putString("status", userProfile.getStatus());
                                bundle.putString("bio", userProfile.getBio());
                                bundle.putString("user_id", userProfile.getUserID());

                                UserDetailFragment userDetailFragment = new UserDetailFragment();
                                userDetailFragment.setArguments(bundle);

                                FragmentManager fragmentManager = getActivity().getSupportFragmentManager();
                                FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

                                fragmentTransaction.replace(R.id.fl_container, userDetailFragment);
                                fragmentTransaction.commit();
                            }
                        });
                    }
                };
        recyclerView.setAdapter(recyclerAdapter);

    }



//This is the code in UserDetailFragment

 public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View v = inflater.inflate(R.layout.fragment_user_detail,
                container, false);
        username = v.findViewById(R.id.user_profile_username);
        display_name = v.findViewById(R.id.user_profile_display_username);
        status = v.findViewById(R.id.user_profile_status);
        bio = v.findViewById(R.id.user_profile_bio);
        follow = v.findViewById(R.id.user_profile_follow);

        Bundle bundle = getArguments();

        String Username = bundle.getString("username");
        String DisplayName = bundle.getString("display_name");
        String Status = bundle.getString("status");
        String Bio = bundle.getString("bio");
        user_id = bundle.getString("user_id");

        username.setText(Username);
        display_name.setText(DisplayName);
        status.setText(Status);
        bio.setText(Bio);

        reference.child(userID).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                UserProfile userProfile = dataSnapshot.getValue(UserProfile.class);
                followerUsername = userProfile.getUsername();
            }

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

            }
        });

        reference.child(user_id).addValueEventListener(new ValueEventListener() {                  //this is where the error causes
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                UserProfile userProfile = dataSnapshot.getValue(UserProfile.class);
                followingUsername = userProfile.getUsername();
            }

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

            }
        });

        reference.child(userID).child("following").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                if (!dataSnapshot.hasChild(user_id)) {
                    follow.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {
                            userFollow();
                        }
                    });
                }else follow.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        userUnfollow();
                    }
                });
            }

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

            }
        });

        return v;
    }