//失败后重试 SDWebImageRetryFailed = 1 << 0,
//UI交互期间开始下载，导致延迟下载比如UIScrollView减速。 SDWebImageLowPriority = 1 << 1,
//只进行内存缓存 SDWebImageCacheMemoryOnly = 1 << 2,
//这个标志可以渐进式下载,显示的图像是逐步在下载 SDWebImageProgressiveDownload = 1 << 3,
//刷新缓存 SDWebImageRefreshCached = 1 << 4,
//后台下载 SDWebImageContinueInBackground = 1 << 5,
//NSMutableURLRequest.HTTPShouldHandleCookies = YES;
SDWebImageHandleCookies = 1 << 6,
//允许使用无效的SSL证书 //SDWebImageAllowInvalidSSLCertificates = 1 << 7,
//优先下载 SDWebImageHighPriority = 1 << 8,
//延迟占位符 SDWebImageDelayPlaceholder = 1 << 9,
//改变动画形象 SDWebImageTransformAnimatedImage = 1 << 10,
