iOS 获取网络链接下的图片宽高

使用SDWebImage 的一个方法完美解决

[[SDWebImageDownloader sharedDownloader]downloadImageWithURL:[NSURL URLWithString:string] options:SDWebImageDownloaderUseNSURLCache progress:^(NSInteger receivedSize, NSInteger expectedSize) {
        } completed:^(UIImage *image, NSData *data, NSError *error, BOOL finished) {
            //这边就能拿到图片了
            nslog(@"%f",image.heigh);
        }];