@Override
    public boolean onItemMove(int fromPosition, int toPosition) {
        Collections.swap(tareasList, fromPosition, toPosition);
        List<String> listOfSortedTareasId = new ArrayList<>();

      for (Tareas tareas: tareasList){
            listOfSortedTareasId.add(tareas.getTareasId());
        }

        //convert the List of Longs to a JSON string
        Gson gson = new Gson();
        String jsonListOfSortedTareas = gson.toJson(listOfSortedTareasId);
        databaseReference.child("Dias").child(day).child("listOrder").setValue(jsonListOfSortedTareas);

        notifyItemMoved(fromPosition, toPosition);
        return true;
    }

List<Tareas> mTareas = sortTareas();
    mTareasAdapter = new TareasAdapter(getActivity(), mTareas);

Query listQuery = mTareasDatabase.child(userId).child("Dias").child(today).child("listOrder");
            listQuery.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    jsonListOfSortedTareasId = dataSnapshot.getValue(String.class);
                    sortTareas();
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });


private List<Tareas> sortTareas() {
        //check for null
        if (jsonListOfSortedTareasId != null) {
            Log.d("sortedCalled", jsonListOfSortedTareasId+"");
                //convert JSON array into a List<Long>
                Gson gson = new Gson();
                List<String> listOfSortedCustomersId = gson.fromJson(jsonListOfSortedTareasId, new TypeToken<List<String>>() {
                }.getType());

                //build sorted list
                if (listOfSortedCustomersId != null && listOfSortedCustomersId.size() > 0) {
                    for (String id : listOfSortedCustomersId) {
                        for (Tareas tareas : mTareasList) {
                            if (tareas.getTareasId().equals(id)) {
                                sortedTareas.add(tareas);
                                mTareasList.remove(tareas);
                                break;
                            }
                        }
                    }
                }
                if (mTareasList.size() > 0) {
                    sortedTareas.addAll(mTareasList);
                }
                return sortedTareas;
            }else {
            return mTareasList;

        }
        }