docs: @Override
      protected void createSharedPreferences() {
          super.createSharedPreferences();
  
          this.sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
  
          // problem that the first call to getAll() returns nothing, apparently the
          // following two calls have to be made to read all the values correctly
          // http://stackoverflow.com/questions/9310479/how-to-iterate-through-all-keys-of-shared-preferences
          this.sharedPreferences.edit().clear();
          PreferenceManager.setDefaultValues(this, R.xml.preferences, true);
  
          this.sharedPreferences.registerOnSharedPreferenceChangeListener(this);
      }