iOS开发数据存储之YYCache

一.关于YYCache

YYCache由YYCache、YYDiskCache、YYMemoryCache和YYKVStorage组成,其中YYKVStorage可直接对sqlite和文件系统进行读写(YYDiskCache的底层实现)

类	存储方式	存取速度(方式)	缓存时间
YYCache	如果不指定存储方式,默认存入内存的时候同时写入磁盘	1.从内存中读,有就直接拿来用;2.没有再从磁盘读,有就拿来用,并写入内存中;3.仍然没有就返回空	和指定存储方式一样
YYMemoryCache	将对象存储在内存中	存取速度较快	短(下次重新启动运用的时候缓存会被清空)
YYDiskCache	将对象存储在磁盘中	存取速度较慢	长(下次重新启动运用的时候缓存仍然存在)

1. 内存缓存(YYMemoryCache)

存储的单元是_YYLinkedMapNode,除了key和value外,还存储了它的前后Node的地址_prev,_next.整个实现基于_YYLinkedMap,它是一个双向链表,除了存储了字典_dic外,还存储了头结点和尾节点.它实现的功能很简单,就是:有新数据了插入链表头部,访问过的数据结点移到头部,内存紧张时把尾部的结点移除.就这样实现了淘汰算法.因为内存访问速度很快,锁占用的时间少,所以用的速度最快的OSSpinLockLock

2. 硬盘缓存(YYDiskCache)

采用的是文件和数据库相互配合的方式.有一个参数inlineThreshold,默认20KB,小于它存数据库,大于它存文件.能获得效率的提高.key:path,value:cache存储在NSMapTable里.根据path获得cache,进行一系列的set,get,remove操作更底层的是YYKVStorage,它能直接对sqlite和文件系统进行读写.每次内存超过限制时,select key, filename, size from manifest order by last_access_time desc limit ?1会根据时间排序来删除最近不常用的数据.硬盘访问的时间比较长,如果用OSSpinLockLock锁会造成CPU消耗过大,所以用的dispatch_semaphore_wait来做.

二.YYCache API解读

/** The name of the cache, readonly. */
@property (copy, readonly) NSString *name;/** The underlying memory cache. see `YYMemoryCache` for more information.*/
@property (strong, readonly) YYMemoryCache *memoryCache;/** The underlying disk cache. see `YYDiskCache` for more information.*/
@property (strong, readonly) YYDiskCache *diskCache;/**Create a new instance with the specified name.Multiple instances with the same name will make the cache unstable.@param name  The name of the cache. It will create a dictionary with the name inthe app's caches dictionary for disk cache. Once initialized you should not read and write to this directory.@result A new cache object, or nil if an error occurs.*/
- (nullable instancetype)initWithName:(NSString *)name;/**Create a new instance with the specified path.Multiple instances with the same name will make the cache unstable.@param path  Full path of a directory in which the cache will write data.Once initialized you should not read and write to this directory.@result A new cache object, or nil if an error occurs.*/
- (nullable instancetype)initWithPath:(NSString *)path NS_DESIGNATED_INITIALIZER;/**Convenience InitializersCreate a new instance with the specified name.Multiple instances with the same name will make the cache unstable.@param name  The name of the cache. It will create a dictionary with the name inthe app's caches dictionary for disk cache. Once initialized you should not read and write to this directory.@result A new cache object, or nil if an error occurs.*/
+ (nullable instancetype)cacheWithName:(NSString *)name;/**Convenience InitializersCreate a new instance with the specified path.Multiple instances with the same name will make the cache unstable.@param path  Full path of a directory in which the cache will write data.Once initialized you should not read and write to this directory.@result A new cache object, or nil if an error occurs.*/
+ (nullable instancetype)cacheWithPath:(NSString *)path;- (instancetype)init UNAVAILABLE_ATTRIBUTE;
+ (instancetype)new UNAVAILABLE_ATTRIBUTE;#pragma mark - Access Methods
///=============================================================================
/// @name Access Methods
///=============================================================================/**Returns a boolean value that indicates whether a given key is in cache.This method may blocks the calling thread until file read finished.@param key A string identifying the value. If nil, just return NO.@return Whether the key is in cache.*/
- (BOOL)containsObjectForKey:(NSString *)key;/**Returns a boolean value with the block that indicates whether a given key is in cache.This method returns immediately and invoke the passed block in background queuewhen the operation finished.@param key   A string identifying the value. If nil, just return NO.@param block A block which will be invoked in background queue when finished.*/
- (void)containsObjectForKey:(NSString *)key withBlock:(nullable void(^)(NSString *key, BOOL contains))block;/**Returns the value associated with a given key.This method may blocks the calling thread until file read finished.@param key A string identifying the value. If nil, just return nil.@return The value associated with key, or nil if no value is associated with key.*/
- (nullable id<NSCoding>)objectForKey:(NSString *)key;/**Returns the value associated with a given key.This method returns immediately and invoke the passed block in background queuewhen the operation finished.@param key A string identifying the value. If nil, just return nil.@param block A block which will be invoked in background queue when finished.*/
- (void)objectForKey:(NSString *)key withBlock:(nullable void(^)(NSString *key, id<NSCoding> object))block;/**Sets the value of the specified key in the cache.This method may blocks the calling thread until file write finished.@param object The object to be stored in the cache. If nil, it calls `removeObjectForKey:`.@param key    The key with which to associate the value. If nil, this method has no effect.*/
- (void)setObject:(nullable id<NSCoding>)object forKey:(NSString *)key;/**Sets the value of the specified key in the cache.This method returns immediately and invoke the passed block in background queuewhen the operation finished.@param object The object to be stored in the cache. If nil, it calls `removeObjectForKey:`.@param block  A block which will be invoked in background queue when finished.*/
- (void)setObject:(nullable id<NSCoding>)object forKey:(NSString *)key withBlock:(nullable void(^)(void))block;/**Removes the value of the specified key in the cache.This method may blocks the calling thread until file delete finished.@param key The key identifying the value to be removed. If nil, this method has no effect.*/
- (void)removeObjectForKey:(NSString *)key;/**Removes the value of the specified key in the cache.This method returns immediately and invoke the passed block in background queuewhen the operation finished.@param key The key identifying the value to be removed. If nil, this method has no effect.@param block  A block which will be invoked in background queue when finished.*/
- (void)removeObjectForKey:(NSString *)key withBlock:(nullable void(^)(NSString *key))block;/**Empties the cache.This method may blocks the calling thread until file delete finished.*/
- (void)removeAllObjects;/**Empties the cache.This method returns immediately and invoke the passed block in background queuewhen the operation finished.@param block  A block which will be invoked in background queue when finished.*/
- (void)removeAllObjectsWithBlock:(void(^)(void))block;/**Empties the cache with block.This method returns immediately and executes the clear operation with block in background.@warning You should not send message to this instance in these blocks.@param progress This block will be invoked during removing, pass nil to ignore.@param end      This block will be invoked at the end, pass nil to ignore.*/
- (void)removeAllObjectsWithProgressBlock:(nullable void(^)(int removedCount, int totalCount))progressendBlock:(nullable void(^)(BOOL error))end;

三.YYCache 使用

1.数据存储

注意:保存的自定义对象要遵守NSCoding的协议

//模拟数据
NSString *value = @"cacheContent";
NSString *key = @"key";
YYCache *yyCache = [YYCache cacheWithName:@"yycache"];
//根据key写入缓存value
[yyCache setObject:value forKey:key];

2.判断缓存是否存在

// 根据key判断缓存是否存在
BOOL isContains = [yyCache containsObjectForKey:key];

3.移除缓存

//根据key移除缓存
[yyCache removeObjectForKey:key];

4.移除所有缓存

//移除所有缓存
[yyCache removeAllObjects];

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