init method
从本地存储恢复用户上次的选择 必须在 SharedPreferencesBaseUtils.getInstance() 完成后调用
Implementation
Future<void> init() async {
// 恢复 themeMode
final modeStr = SharedPreferencesBaseUtils.getString(_kThemeMode);
_themeMode = _parseThemeMode(modeStr);
// 恢复自定义主题标识
final custom = SharedPreferencesBaseUtils.getString(_kCustomTheme);
_customTheme = custom.isEmpty ? null : custom;
notifyListeners();
}