@Override
  public void onConstruct() {
    super.onConstruct();

    String json = preferenceService.getString(PREF_KEY_NOTES, null);
    List<Note> notes;
    if (json != null) {
      notes = gson.fromJson(json, new TypeToken<List<Note>>() {}.getType());
    } else {
      notes = new ArrayList<>();
    }
    getModel().setNotes(notes);
    getModel().setSelectedNoteIds(new ArrayList<Long>());
  }
 private void persistNotes() {
   preferenceService.edit().putString(PREF_KEY_NOTES, gson.toJson(getModel().getNotes())).commit();
 }