sd加载动画

[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 = 1;
                       transition.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
                       [weakself.layer addAnimation:transition forKey:nil];
                   }
               }];