Why getting the Instance of SharedPreferences is an async function? Is it a good practice to cache the instance?

Question

I wonder why is SharedPreferences.getInstance() an async function?! I want to cache the instance in a static variable and use it to store settings data without having to use await or SharedPreferences.getInstance().then(...), but if they made it async, it should be for a good reason, any ideas?

Answer 1

SharedPreferences.getInstance() actually fetches the data and does not only provide a reference to a SharedPreferences's instance

based on the source code

  static Future<SharedPreferences> getInstance() async {
    if (_completer == null) {
      _completer = Completer<SharedPreferences>();
      try {
        final Map<String, Object> preferencesMap =
            await _getSharedPreferencesMap();
        _completer.complete(SharedPreferences._(preferencesMap));
      } on Exception catch (e) {
        // If there's an error, explicitly return the future with an error.
        // then set the completer to null so we can retry.
        _completer.completeError(e);
        final Future<SharedPreferences> sharedPrefsFuture = _completer.future;
        _completer = null;
        return sharedPrefsFuture;
      }
    }
    return _completer.future;
  }

and

  static Future<Map<String, Object>> _getSharedPreferencesMap() async {
    final Map<String, Object> fromSystem = await _store.getAll();
    assert(fromSystem != null);
    // Strip the flutter. prefix from the returned preferences.
    final Map<String, Object> preferencesMap = <String, Object>{};
    for (String key in fromSystem.keys) {
      assert(key.startsWith(_prefix));
      preferencesMap[key.substring(_prefix.length)] = fromSystem[key];
    }
    return preferencesMap;
  }

I don't know if this was trivial, but it wasn't for me, I thought data are being fetched only on get functions.