채팅방에 사람 목록을 띄우려고 네비게이션바를 만든 뒤 리사이클러뷰를 짰습니다. 그런데 화면에 나오지 않네요 ㅠㅠ 혹시 왜 그런지 아시는 분 계신가요?

class MemberRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    List<UserModel> userModel  = new ArrayList();

    public MemberRecyclerViewAdapter() {



        String destinatonUid1 = getIntent().getStringExtra("chat-destinationUid");

        FirebaseDatabase.getInstance().getReference().child("users").child(destinatonUid1).addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull @NotNull DataSnapshot snapshot) {

                UserModel userModels;

                userModels = snapshot.getValue(UserModel.class);

                userModel.add(userModels);

                System.out.println(userModel.get(0).nickname);
            }


            @Override
            public void onCancelled(@NonNull @NotNull DatabaseError error) {

            }


        });


    }

    @NonNull
    @NotNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull @NotNull ViewGroup parent, int viewType) {

        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_chatroom_people,parent,false);

        return new MemberViewHolder(view);


    }

    @Override
    public void onBindViewHolder(@NonNull @NotNull RecyclerView.ViewHolder holder, int position) {

        MemberViewHolder memberViewHolder = ((MemberViewHolder)holder);

        System.out.println(userModel.get(0).nickname);
        memberViewHolder.member_ninckname.setText(userModel.get(0).nickname);

        Glide.with(holder.itemView.getContext())
                .load(userModel.get(0).imageUri)
                .apply(new RequestOptions().circleCrop())
                .into(memberViewHolder.member_profile);

    }

    @Override
    public int getItemCount() {
        return userModel.size();
    }

    private class MemberViewHolder extends RecyclerView.ViewHolder {

        public TextView member_ninckname;
        public ImageView member_profile;


        public MemberViewHolder(View view) {
            super(view);

            member_ninckname = (TextView)view.findViewById(R.id.memeber_nickname);
            member_profile = (ImageView)view.findViewById(R.id.memeber_profile);


        }
    }


}

대화상대 부분에 상대방의 닉네임과 프로필이 뜨는 것이 목적이고, 사람은 1대1 채팅방에 상대 1명이라 position(0)이라고 했습니다.