func saveImage() {
        UIImageWriteToSavedPhotosAlbum(imageToSave, self, #selector(TKLongImageViewController.image(image:didFinishSavingWithError:contextInfo:)), nil)
    }
    
    func image(image: UIImage, didFinishSavingWithError error: NSError?, contextInfo:UnsafeRawPointer) {
        if error == nil {
            let ac = UIAlertController(title: "保存成功", message: "图片已经保存到相册啦", preferredStyle: .alert)
            ac.addAction(UIAlertAction(title: "好的", style: .default, handler: nil))
            present(ac, animated: true, completion: nil)
        } else {
            let ac = UIAlertController(title: "出错了~", message: error?.localizedDescription, preferredStyle: .alert)
            ac.addAction(UIAlertAction(title: "好的", style: .default, handler: nil))
            present(ac, animated: true, completion: nil)
        }
    }