Firestore not retrieving all documents from a collection

Question

So I have a collection like this:

Rooms(collection)
    -C1(document)
    -D1(document) 
    -E1(document)
    -F1(document)

I want to get all the documents here, and put them in a list.

My code so far(RoomList is a private global variable that I initialize in the onCreate):

private void getRooms (){

    CollectionReference rooms = db.collection("Rooms");
    rooms.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
        @Override
        public void onComplete(@NonNull Task<QuerySnapshot> task) {
            if(task.isSuccessful()){
                for (DocumentSnapshot document : task.getResult()){
                    Room r = new Room();
                    r.setRoomNumber(document.getId());
                    Map<String, Object> data = document.getData();
                    r.setDescription(data.get("Description").toString());
                    RoomList.add(r);
                }
            }
        }
    })

Every time I run the debugger, it completely skips over the onComplete method, and doesn't change the RoomList.

Answer 1

Your RoomList is always empty because onComplete() method is called asynchronous which means that is called even before you are trying to add those objects of Room class to the list. To solve this, you need to move the declaration of your list inside the onComplete method like this:

private void getRooms (){
    CollectionReference rooms = db.collection("Rooms");
    rooms.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
        @Override
        public void onComplete(@NonNull Task<QuerySnapshot> task) {
            List<Room> list = new ArrayList<>();
            if(task.isSuccessful()){
                for (DocumentSnapshot document : task.getResult()){
                    Room r = new Room();
                    r.setRoomNumber(document.getId());
                    Map<String, Object> data = document.getData();
                    r.setDescription(data.get("Description").toString());
                    RoomList.add(r);
                }
            }
            Log("TAG", list);
        }
    })
}