实现简易缓存功能

最近公司项目增加了个需求：为了更好的用户体验，节省用户流量，需要实现离线缓存功能

针对这个需求临时创建了一个简易的缓存管理类，负责管理缓存，其可对数据进行缓存或从缓存中取出或删除缓存。

创建缓存目录：

- (id)init
{
    if ((self = [super init])) {
        // 创建缓存目录
        NSString* cachesDirectory = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES)[0];
        _directory = [[[cachesDirectory stringByAppendingPathComponent:[[NSBundle mainBundle] bundleIdentifier]] stringByAppendingPathComponent:@"XXXXXX"] copy];
        [[NSFileManager defaultManager]createDirectoryAtPath:_directory withIntermediateDirectories:YES attributes:nil error:NULL];
        
        // 获取后台优先级的、并发的、全局的线程队列
        _diskQueue = dispatch_queue_create("com.XXXXXX.cache", DISPATCH_QUEUE_SERIAL);
        dispatch_queue_t priority = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);
  dispatch_set_target_queue(priority, _diskQueue);

    }
    return self;
}

把数据写入缓存：

- (void)setObject:(id)anObject forKey:(NSString*)key
{   
        NSData *data = [NSKeyedArchiver archivedDataWithRootObject:anObject];  
  
        NSString* cachePath = cachePathForKey(_directory, key);
        dispatch_async(_diskQueue, ^{   
        [data writeToFile:cachePath atomically:YES];    
        });
}

从缓存中取出数据:

- (id<NSCoding>)objectForKey:(NSString*)key{
    if([self hasCacheForKey:key]) {               
             NSData *data =  [NSData dataWithContentsOfFile:cachePathForKey(_directory, key) options:0 error:NULL];     
           return [NSKeyedUnarchiver unarchiveObjectWithData:data];
    }else {     
           return nil;  
          }
}

清除缓存数据：

- (void)clearAllCache{    
          dispatch_sync(_diskQueue, ^{        
               NSDirectoryEnumerator *dirEnum = [[NSFileManager defaultManager] enumeratorAtPath:_directory];      
               NSString *fileName;        
             while (fileName= [dirEnum nextObject]) {    
        [[NSFileManager defaultManager] removeItemAtPath: [NSString stringWithFormat:@"%@/%@",_directory, fileName] error:NULL];                     }  
    });
}