content: import 'package:shared_preferences/shared_preferences.dart';
  
  class LocalPref extends Pref {
    @override
    Future<bool> saveString(String key, String value) async {
      final prefs = await SharedPreferences.getInstance();
      return prefs.setString(key, value);
    }
  
    @override
    Future<String> getString(String key) async {
      final prefs = await SharedPreferences.getInstance();
      return Future.value(prefs.getString(key));
    }
  }
  
  class MemoryPref extends Pref {
    Map<String, Object> memoryMap = new Map<String, Object>();
  
    @override
    Future<String> getString(String key) {
      return Future.value(memoryMap[key] as String?);
    }
  
    @override
    Future<bool> saveString(String key, String value) async {
      memoryMap[key] = value;
      return Future.value(true);
    }
  }
  
  abstract class Pref {
    Future<bool> saveString(String key, String value);
  
    Future<String> getString(String key);
  }
  
  class DATA_CONST {
    static const String CACHE_SHOW = "CACHE_SHOW";
    static const String CACHE_CINE = "CACHE_CINE";
    static const String CACHE_BOOK_TIME_SLOT = "CACHE_BOOK_TIME_SLOT";
    static const String CACHE_SELECTED_TIME_SLOT = "CACHE_SELECTED_TIME_SLOT";
    static const String CACHE_OTHER_TIME_SLOT = "CACHE_OTHER_TIME_SLOT";
  }
  