这一篇讲讲不常用的一些方法。
1 sd_setImageWithPreviousCachedImageWithURL: placeholderImage: options: progress: completed:
取得上次缓存的图片，然后作为占位图的参数再次进行一次图片设置。
- (void)sd_setImageWithPreviousCachedImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholder options:(SDWebImageOptions)options progress:(SDWebImageDownloaderProgressBlock)progressBlock completed:(SDWebImageCompletionBlock)completedBlock {
NSString *key = [[SDWebImageManager sharedManager] cacheKeyForURL:url];
UIImage *lastPreviousCachedImage = [[SDImageCache sharedImageCache] imageFromDiskCacheForKey:key];
[self sd_setImageWithURL:url placeholderImage:lastPreviousCachedImage ?: placeholder options:options progress:progressBlock completed:completedBlock];
}
