[cell.photo sd_setImageWithURL:[NSURL URLWithString:ad.imageUrl] placeholderImage:[UIImage imageNamed:@"xyDefaultImage1"] completed:^(UIImage *image, NSError *error, EMSDImageCacheType cacheType, NSURL *imageURL) {
imgHeight = image.size.height * [UIScreen mainScreen].bounds.size.width / image.size.width;
weakCell.photo.image = image;
weakCell.photoHeightConstraint.constant = imgHeight;
用了Autolayout，特别是变化大的界面，经常要重新抽出来重新调
