Question

具有泛型的磁盘缓存我是一位来自JavaScript和PHP的程序员，并且正在Flutter上开发App，并且难以在手机的内部存储中实现缓存。

我想了解并知道是否可以为JSON创建带有序列化的泛型类型类，以便可以将其存储在文件中。我已经在内存中完成了Cache的实现，并且运行良好，再加上磁盘上的Cache的实现，我遇到了困难。

内存缓存代码

class MemCache<T> extends Cache<T> {

  Duration cacheValidDuration = Duration(minutes: 30);
  DateTime lastFetchTime = DateTime.fromMillisecondsSinceEpoch(0);
  RList<T> allRecords = RList<T>();

  //is updade cache
  bool isShouldRefresh() {
    return (null == allRecords ||
        allRecords.isEmpty ||
        null == lastFetchTime ||
        lastFetchTime.isBefore(DateTime.now().subtract(cacheValidDuration)));
  }

  @override
  Future<RList<T>> getAll() {
    return Future.value(allRecords);
  }

  @override
  Future<void> putAll(RList<T> objects) {
    allRecords.addAll(objects);
    lastFetchTime = DateTime.now();
  }

  @override
  Future<void> putAllAsync(Future<RList<T>> objects) async {
    allRecords = await objects;
  }


}

磁盘缓存代码 如何从泛型调用序列化方法

class DiskCache<T> extends Cache<T> {

  Duration cacheValidDuration = Duration(minutes: 30);
  DateTime lastFetchTime = DateTime.fromMillisecondsSinceEpoch(0);
  RList<T> allRecords = RList<T>();

  //is update the cache 
  bool isShouldRefresh() {
    return (null == allRecords ||
        allRecords.isEmpty ||
        null == lastFetchTime ||
        lastFetchTime.isBefore(DateTime.now().subtract(cacheValidDuration)));
  }

  @override
  Future<RList<T>> getAll() async {
    await _readFromDisk();
    return Future.value(allRecords);
  }

  @override
  Future<void> putAll(RList<T> objects) async {
    allRecords.addAll(objects);
    lastFetchTime = DateTime.now();
    await _writeToDisk();
  }

  @override
  Future<void> putAllAsync(Future<RList<T>> objects) async {
    allRecords = await objects;
    lastFetchTime = DateTime.now();
    await _writeToDisk();
  }

  //parth
  Future<String> get _localPath async {
    final directory = await getApplicationDocumentsDirectory();
    return directory.path;
  }

  //file pointer
  Future<File> get _localFile async {
    final path = await _localPath;
    return File('$path/allRecords.json');
  }

  //write to file
  Future<File> _writeToDisk() async {
    try {
      File recordedFile;
      if (allRecords != null) {
        var map = allRecords.map((c) {
          var item = c as ISerialization;
          return item.toJson();
        }).toList();

        var jsonString = jsonEncode(map);

        final file = await _localFile;
        // Write the file
        recordedFile = await file.writeAsString(jsonString);
      }
      return recordedFile;
    } catch (e) {
      print("writeToDisk: " + e.toString());
      return null;
    }
  }
// ************************** issues on this part ******************
  Future<RList<T>> _readFromDisk() async {
    try {
      final file = await _localFile;

      // Read the file
      String contents = await file.readAsString();
      var parsedJson = jsonDecode(contents);

      if (allRecords == null) {
        allRecords = RList<T>();
      }
      allRecords.clear();

      for (var item in parsedJson) {
       // ************************** issues on this part ******************
        print(T.fromMap(item));
        allRecords.add(T.fromMap(item));
      }

      return allRecords;
    } catch (e) {
      print("readFromDisk: " + e.toString());
      return null;
    }
  }
}

错误：未为类“ Type”定义方法“ fromMap”。 -“类型”来自“ dart：core”。尝试将名称更正为现有方法的名称，或定义一个名为“ fromMap”的方法。 allRecords.add（T.fromMap（item））; ^^^^^^^^

如何从泛型

0 个答案: