图片缓存 swift 3

Question

您好，我想缓存来自 json 的图像。我创建了一个网络服务，它下载并解析 json，我使用 func downloadImage() 发出 imageurl.Then 的 http 请求，我用这个 func 更新了我的剧集，但图像仍在滚动下载

    var episode: Product! {   
        didSet {

            self.updateUI()
        }
    }



let imageCache = NSCache<AnyObject, AnyObject>()

    func updateUI()
    {
        menuItemNameLabel?.text = episode.title
        ingredientsItemLabel?.text = episode.summary
        priceItemLabel?.text = episode.price
        menuItemImageView?.image = UIImage(named: "Koulourades")

        if let thumbnailURL = episode.thumbnailURL {
            let networkService = NetworkService(url: thumbnailURL)
            networkService.downloadImage({ (imageData) in


                if let imageFromCache = self.imageCache.object(forKey: self.episode.thumbnailURL as AnyObject) as? UIImage {

                    DispatchQueue.main.async(execute: {
                         self.menuItemImageView?.image = imageFromCache
                         return
                    })
                }


               DispatchQueue.main.async(execute: {
                    let imageToCache = UIImage(data: imageData as Data)
                    self.imageCache.setObject(imageToCache!, forKey: self.episode.thumbnailURL as AnyObject)

                    self.menuItemImageView?.image = imageToCache
                })


            })
        }
    }//--end updateUI()