SDWebImage图片下载完成后渐进显示图片

[self sd_setImageWithURL:[NSURL URLWithString:imageURL]

placeholderImage:placeholder

completed:^(UIImage * _Nullable image, NSError * _Nullable error, SDImageCacheType cacheType, NSURL * _Nullable imageURL) {

if (image && cacheType == SDImageCacheTypeNone) {

CATransition *transition = [CATransition animation];

transition.type = kCATransitionFade;

transition.duration = 0.3;

transition.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];

[weakself.layer addAnimation:transition forKey:nil];

}

}];