NSOperation下载图片-04

cell 的图片下载

1，面试题

1》如何防止一个url对应的图片重复下载？

＊cell下载图片－有沙盒缓存

2》SDWebImage的默认缓存时长是多少？

＊一个星期

3》SDWebImage底层是怎样实现的？

＊cell下载图片－有沙盒缓存

2，SDWebImage

1》常用方法

- (void)sd_setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholder;

- (void)sd_setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholder options:(SDWebImageOptions)options;

- (void)sd_setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholder completed:(SDWebImageCompletionBlock)completedBlock;

- (void)sd_setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholder options:(SDWebImageOptions)options progress:(SDWebImageDownloaderProgressBlock)progressBlock completed:(SDWebImageCompletionBlock)completedBlock;

2》内存处理：当app接收到内存警告时

// 当app接收到内存警告

- (void)applicationDidReceiveMemoryWarning:(UIApplication *)application

{

    SDWebImageManager *mgr = [SDWebImageManager sharedManager];

    

    // 1,取消正在下载对操作

    [mgr cancelAll];

    

    // 2,清除内存缓存

    [mgr.imageCache clearMemory];

    

//    mgr.imageCache.maxCacheAge = 1 * 24 * 60 * 60 * 7; // one week

//    mgr.imageCache.maxCacheSize // bytes

}

3》SDWebImageOptions参数

＊SDWebImageRetryFailed：下载失败后，会自动尝试下载

＊SDWebImageLowPriority：当正在进行一些UI交互时，自动暂停内部一些下载操作

＊SDWebImageRetryFailed ｜ SDWebImageLowPriority：拥有上面2个功能