can not delete cache file

[leetomlee123]

    if (toRemove.contains(cacheObject.id)) return;

    toRemove.add(cacheObject.id!);
    if (_memCache.containsKey(cacheObject.key)) {
      _memCache.remove(cacheObject.key);
    }
    if (_futureCache.containsKey(cacheObject.key)) {
      await _futureCache.remove(cacheObject.key);
    }
    final file = io.File(cacheObject.relativePath);

    if (file.existsSync()) {
      try {
        await file.delete();
        // ignore: unused_catch_clause
      } on PathNotFoundException catch (e) {
        // File has already been deleted. Do nothing #184
      }
    }

cacheObject.relativePath is not real abs file path ,delete file can not work
class CustomCacheManager { static const key = 'tsl'; static final fileSystem = ExternalStorageFileSystem(key); static CacheManager instance = CacheManager( Config(key, stalePeriod: const Duration(days: 30), maxNrOfCacheObjects: 999999999, fileSystem: fileSystem), ); }
`
class ExternalStorageFileSystem implements FileSystem {
final Future _fileDir;
final String _cacheKey;

ExternalStorageFileSystem(this._cacheKey)
: _fileDir = createDirectory(_cacheKey);

static Future createDirectory(String key) async {
final baseDir = await getExternalStorageDirectory();
final path = p.join(baseDir!.path, key);

const fs = LocalFileSystem();
final directory = fs.directory(path);
await directory.create(recursive: true);
return directory;

}

@OverRide
Future createFile(String name) async {
final directory = await _fileDir;
if (!(await directory.exists())) {
await createDirectory(_cacheKey);
}
return directory.childFile(name);
}

void emptyCache() async {
final directory = await _fileDir;
if (await directory.exists()) {
await directory.delete(recursive: true);
}
}
}
`