public static OSMTileDownloader.OSMMap getCurrentMapSource() {
    String mapSourceString = pref.getString(CURRENT_MAP_SOURCE, null);
    if (mapSourceString == null) return null;

    return StringUtils.GSON.fromJson(mapSourceString, OSMTileDownloader.OSMMap.class);
  }
 public static void saveCurrentMapSource(OSMTileDownloader.OSMMap map) {
   String mapSource = StringUtils.GSON.toJson(map, OSMTileDownloader.OSMMap.class);
   editor.clear();
   editor.putString(CURRENT_MAP_SOURCE, mapSource);
   editor.commit();
 }