@interface
             VSPreference : NSObject


            /*
            * 用于管理需要持久化的普通状态量，可理解为不属于这4个模块(dynamicPreference / memoryPreference / switchPreference / userPreference)的状态量 
            */
+ (VSDefaultPreference *)defaultPreference;

/** 动态资源，APP动态配置的资源，APP启动时，请求接口返回 */
+ (VSDynamicPreference *)dynamicPreference;

/** 用于管理不需要持久化的配置项，仅存在内存中。比如某个接口数据返回，需要记录某个字段的值 */
+ (VSMemoryPreference *)memoryPreference;

/** 运营开关，降级开关，APP启动时请求接口返回 */
+ (VSSwitchPreference *)switchPreference;

/** 用于管理记录用户行为的配置项，如：记录提示页是否展示过，记录提示页上次展示的时间 */
+ (VSUserPreference *)userPreference;

@end

            //
             给数据表增加一个key-value
            void VSKeyValueSetKeyValueToTable(FMDatabase *db, NSString *key, id value, NSString *tableName) {
    NSDictionary<NSString *, id> *JSONObject = @{ key: value };
    // [JSONObject yy_modelToJSONData]可能是因为多线程修改了内容导致崩溃
    NSData *data = [[JSONObject copy] yy_modelToJSONData];
    if (!data) {
#if DEBUG
        dispatch_async(dispatch_get_main_queue(), ^{
            @throw [NSException exceptionWithName:@"Key-Value 不是有效的JSON对象(上报到RTX吧)" reason:@"保持统一性" userInfo:nil];
        });
#endifreturn;
    }
    NSString *SQLScript = [NSString stringWithFormat:kSQLFormatterForReplaceValue, tableName, key];
    [db executeUpdate:SQLScript, data];
}

// 从数据表里删除key-valuevoid VSKeyValueRemoveKeyValueToTable(FMDatabase *db, NSString *key, NSString *tableName) {
    NSString *SQLScript = [NSString stringWithFormat:kSQLFormatterForDeleteValue, tableName, key];
    [db executeUpdate:SQLScript];
}

            /*
            *
 * 监听值的变化
 * 1、将需要变化的keyValue都存储到VSKeyValueStackCachedChangeObjects中
 * 2、每隔1秒，将VSKeyValueStackCachedChangeObjects中的keyValue拷贝到局部变量cachedChangeObjects中，并清空VSKeyValueStackCachedChangeObjects里面所有的数据
 * 3、将cachedChangeObjects循环存储到sqlite中
 
            */
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id<VSKeyValueModel>)object change:(NSDictionary<NSString *, id> *)change context:(void *)context {
    if (context != VSKeyValueStackObserverContext) {
        return;
    }
    
    void(^batchHandler)(void) = ^(void) {
        UIBackgroundTaskIdentifier __block taskToken = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:NULL];
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), VSKeyValueStackCachedChangeQueue, ^{
            NSArray<__VSKeyValueChange *> *cachedChangeObjects = [VSKeyValueStackCachedChangeObjects copy];
            [VSKeyValueStackCachedChangeObjects removeAllObjects];
            [self handleTransaction:^(FMDatabase *db) {
                for (__VSKeyValueChange *__change in cachedChangeObjects) {
                    @autoreleasepool {
                        if (IsEmpty(__change.value)) {
                            VSKeyValueRemoveKeyValueToTable(db, __change.key, __change.tableName);
                        } else {
                            VSKeyValueSetKeyValueToTable(db, __change.key, __change.value, __change.tableName);
                        }
                    }
                }
                [[UIApplication sharedApplication] endBackgroundTask:taskToken];
                taskToken = UIBackgroundTaskInvalid;
            }];
        });
    };
    
    id value = change[NSKeyValueChangeNewKey];
    dispatch_async(VSKeyValueStackCachedChangeQueue, ^{
        if (!VSKeyValueStackCachedChangeObjects.count) {
            batchHandler();
        }
        __VSKeyValueChange *__change = [__VSKeyValueChange new];
        __change.tableName = [object keyValueTableName];
        __change.key = keyPath;
        __change.value = value;
        [VSKeyValueStackCachedChangeObjects addObject:__change];
    });
}

            @implementation
             VSUserPreference

- (instancetype)initWithKeyValueStack
{
    self = [super initWithKeyValueStack];
    if (self) {
        [self addKeyPathObserverToKeyValueStack];
    }
    return self;
}

- (void)dealloc
{
    [self removeKeyPathObserverFromKeyValueStack];
}

#pragma mark - <VSKeyValueModel>

- (NSString *)keyValueTableName
{
    return@"UserPreference";
}

// 设置属性默认值
- (void)setUpWithDefaultValue
{
    _themeStyle = 0;
    _checkoutAgreeProtocolsMap = @{};
}

@end