保存图片到相册

#pragma mark 保存图片到相册
- (void)saveImage:(NSString *)urlString {
    
    NSURL *url = [NSURL URLWithString: urlString];
    SDWebImageManager *manager = [SDWebImageManager sharedManager];
    __block UIImage *img;
    [manager diskImageExistsForURL:url completion:^(BOOL isInCache) {
        if (isInCache) {
            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);
    }];
}
//保存图片完成之后的回调
- (void)image:(UIImage *)image didFinishSavingWithError:(NSError *)error
  contextInfo:(void *)contextInfo
{
    // Was there an error?
    if (error != NULL)
    {
        // Show error message…
        NSLog(@"图片保存失败");
    }
    else  // No errors
    {
        // Show message image successfully saved
        NSLog(@"图片保存成功");
    }
}