saving-cache-file.dart

 Future<File> _getCacheFile() async {
    final dir = (await getApplicationDocumentsDirectory()).path;
    return new File('$dir/hotlist.xml');
  }

  Future<XmlDocument> _getHotListCache() async {
    try {
      final file = await _getCacheFile();
      return parse(await file.readAsString());
    }
    on FileSystemException {
      return _getDefaultHotGameInfo();
    }
  }

  Future<bool> _hotListCacheFileExists() async =>
      await (await _getCacheFile()).exists();


  Future<Null> _saveHotListToCache(XmlDocument doc) async {
    try {
      final file = await _getCacheFile();
      final sink = await file.openWrite();
      await sink.write(doc.toXmlString(pretty: true));
      await sink.close();
      final prefs = await SharedPreferences.getInstance();
      final later = new DateTime.now().add(new Duration(hours: 8));
      prefs.setInt(NEXT_CACHE_UPDATE_EPOCH_KEY, later.millisecondsSinceEpoch);
      setState(() {
        _nextUpdate = new DateTime.fromMicrosecondsSinceEpoch(
            later.millisecondsSinceEpoch * 1000);
        _lastUpdate = new DateTime.now();
      });
      await prefs.commit();
    }
    catch (exception) {
      debugPrint(exception);
    }
  }