notifyDataSetChanged 在片段上无法正常工作

如标题所述；我发现自己无法正确更新所需的片段。

我有一个向用户显示通知的片段，每次将文档添加到类/数据库时都应该更新它。但是，当我从数据库中手动删除文档时，该类似乎没有更新，而是显示了以前在数据库中找到的文档。此外，如果我打开和关闭应用程序，它确实会显示当前文档。

分段：

public class NotificationFragment extends android.support.v4.app.Fragment {

private RecyclerView mNotificationList;
private NotificationsAdapter notificationsAdapter;
private List<Notifications> mNotifList;
private FirebaseFirestore mFirestore;


public NotificationFragment() {
    // Required empty public constructor
}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View v = inflater.inflate(R.layout.fragment_notification, container, false);


    mNotifList = new ArrayList<>();

    mNotificationList = (RecyclerView) v.findViewById(R.id.notification_list);
    notificationsAdapter = new NotificationsAdapter(getContext(), mNotifList);


    mNotificationList.setHasFixedSize(true);
    mNotificationList.setLayoutManager(new LinearLayoutManager(container.getContext()));
    mNotificationList.setAdapter(notificationsAdapter);

    mFirestore = FirebaseFirestore.getInstance();

    String current_user_id = FirebaseAuth.getInstance().getCurrentUser().getUid();

    mFirestore.collection("Users").document(current_user_id).collection("Notifications").addSnapshotListener(requireActivity(), new EventListener<QuerySnapshot>() {
        @Override
        public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {
            if (documentSnapshots != null && !documentSnapshots.isEmpty()) {
                for (DocumentChange doc : documentSnapshots.getDocumentChanges()) {
                    if (doc.getType() == DocumentChange.Type.ADDED) {
                        Notifications notifications = doc.getDocument().toObject(Notifications.class);
                        mNotifList.add(notifications);
                        notificationsAdapter.notifyDataSetChanged();

                    }
                }

            }
        }
    });


    return v;
}

数据库结构：