【SDWebImage】检测有没有缓存图片和把图片保存到相册

NSURL *url = [NSURL URLWithString:model.imageUrl];
    SDWebImageManager *manager = [SDWebImageManager sharedManager];
    UIImage *img;
    if ([manager diskImageExistsForURL:url])
    {
        img =  [[manager imageCache] imageFromDiskCacheForKey:url.absoluteString];
        
    }
    else
    {
        //从网络下载图片
        NSData *data = [NSData dataWithContentsOfURL:url];
        img = [UIImage imageWithData:data];
    }
    // 保存图片到相册中
    UIImageWriteToSavedPhotosAlbum(img,self, @selector(image:didFinishSavingWithError:contextInfo:),nil);

- (void)image:(UIImage *)image didFinishSavingWithError:(NSError *)error
  contextInfo:(void *)contextInfo
{
    // Was there an error?
    if (error != NULL)
    {
        // Show error message…
        
    }
    else  // No errors
    {
        // Show message image successfully saved
    }
}