FireBase Recycler Adapter doesn't retrieve data from FireBase

Question

My database looks like this

I'm trying to fetch all this data from that USER ID inside Cart. But my RecyclerView shows nothing. After checking, the adapter.getItemCount() returns 0. Where did I wrong? This is my code :

onStart()

private void loadData(){
        auth = FirebaseAuth.getInstance().getCurrentUser();
        userID = auth.getUid();
        final DatabaseReference cartList = FirebaseDatabase.getInstance().getReference().child("Cart");
        FirebaseRecyclerOptions<Cart> options =
                new FirebaseRecyclerOptions.Builder<Cart>()
                .setQuery(cartList.child(userID),Cart.class).build();
        FirebaseRecyclerAdapter<Cart,CartHolder> adapter
                = new FirebaseRecyclerAdapter<Cart, CartHolder>(options) {
            @Override
            protected void onBindViewHolder(@NonNull CartHolder holder, int position, @NonNull Cart model) {
                holder.txtGia.setText(model.getTotal());
            }

            @NonNull
            @Override
            public CartHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
                View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.cart_item,parent,false);
                CartHolder holder = new CartHolder(view);
                return holder;
            }
        };
        recyclerView.setAdapter(adapter);
        adapter.startListening();
    }

Model

    public class Cart {
        public String pID,num,time,addr,total,userID;
        public Cart(){}
    
        public Cart(String num,String pID,String time,String addr,String total,String userID) {
            this.num = num;
            this.pID = pID;
            this.time = time;
            this.addr = addr;
            this.total = total;
            this.userID = userID;
        }
    
        public String getNum() {
            return num;
        }
    
        public String getpID() {
            return pID;
        }
    
        public String getTime() {
            return time;
        }
    
        public String getAddr() {
            return addr;
        }
    
        public String getTotal() {
            return total;
        }
    
        public String getUserID() {
            return userID;
        }
    }

and ViewHolder

public class CartHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

    public ImageView shibaImg;
    public TextView txtTen,txtMota,txtGia,txtThoigian;
    ItemClickListener listener;

    public CartHolder(@NonNull View itemView) {
        super(itemView);
        shibaImg = (ImageView) itemView.findViewById(R.id.cart_item_img);
        txtTen = (TextView) itemView.findViewById(R.id.cart_item_ten);
        txtMota = (TextView) itemView.findViewById(R.id.cart_item_mota);
        txtGia = (TextView) itemView.findViewById(R.id.cart_item_gia);
        txtThoigian = (TextView) itemView.findViewById(R.id.cart_item_history);

    }
    public void setItemClickListener(ItemClickListener listener){
        this.listener = listener;
    }

    @Override
    public void onClick(View v) {
        listener.onClick(v, getAdapterPosition(),false);
    }
}

Answer 1

This code seems to be the problem:

cartList.orderByChild("userID").equalTo(userID)

This code takes every child nodes directly under cartList and orders them on their userID property. But there is no userID property in your screenshot, so this results in an empty list.

My best guess is that the key of each node under cartList is the user ID, in which case you can instead use:

cartList.child(userID)

So:

final DatabaseReference cartList = FirebaseDatabase.getInstance().getReference().child("Cart");
FirebaseRecyclerOptions<Cart> options =
        new FirebaseRecyclerOptions.Builder<Cart>()
        .setQuery(cartList.child(userID),Cart.class).build();