A wrapper of disk storage allows people to cache files to disk more securely without worrying about taking up disk space unlimitedly.

Using FixSizedStorage instead of storing cached files roughly, you get:

  • No longer worry about taking up disk space unlimited
  • No longer worry about the operating system deleting cached data
  • Excellent performance, basically equivalent to key to value access of Map


parameter namedtypedescriptiondefaults
idStringunique identification of storage-
capacityintstorage limit5GB


  • How to use FixSizedStorage
fixSizedStorage = FixSizedStorage('example', capacity: 1024);  // Initialize FixSizedStorage with [id] and [capacity]
await fixSizedStorage.init();  // Need to execute [init] after each initialization

String keyStr = '$key';  // Convert [key] to String so that it can be used as the key of fixSizedStorage
String value = await fixSizedStorage.get(keyStr);  // Try to get the cached [value] through [key]
if (value == null) {  // If [key] is not in the cache, [value] is null at this time, and you need to try to insert a new [key]-[value] into the storage
  String path = await fixSizedStorage.touch(keyStr);  // Path to get cached data
  await File(path).writeAsBytes(bytes);  // do something you want
  bool set = await fixSizedStorage.set(keyStr, path);  // Try to insert [key]-[value] into storage, return true if successful, otherwise return false
  value = path;


Each time you create an instance of FixSizedStorage, you need to call init() to fish the data cached in the disk into the memory

The key passed to FixSizedStorage should be able to be a valid file name

After executing the set method of FixSizedStorage, you should no longer write to the cache file (that is, the file corresponding to path); if you do a write operation, you need to execute the set method of FixSizedStorage again to adjust file size

If the set method of FixSizedStorage returns false, then it means the insertion of key and value into FixSizedStorage failed, and the file corresponding to path will also be deleted


  • If the program crashes when the user does something or the operating system causes the file stored at this time to be damaged, how to identify the damaged file
  • Optimize the _deleteFirstDeactiveKeyValue function to reduce the times of delete or set key-value