By default, when a URL fail to be downloaded, the URL is blacklisted so the library won't keep trying.
This flag disable this blacklisting.默認(rèn)情況下, 當(dāng)一個(gè) 圖片URL下載失敗, 這個(gè) URL 會(huì)被加入黑名單, 所以 SDWebImage 不會(huì)再下載這個(gè)資源.
SDWebImageRetryFailed 這個(gè)標(biāo)記可以取消黑名單.
SDWebImageRetryFailed = 1 << 0,
[cell.imageView setImageWithURL:urlt
placeholderImage:[UIImage imageNamed:@"default.jpg"]
options:SDWebImageRetryFailed];