Ios 在 tableview 中下载图像缩略图时如何提高滚动性能

我的应用程序从Imgur下载高分辨率图像时的滚动性能很慢.奇怪的是，图像正在出列和渲染.下面是下载图像的代码.我认为缓存机制不起作用.我该怎么解决这个问题？

 func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "PhotoTableViewCell", for: indexPath) as! PhotoTableViewCell
        cell.descrpiptionLabel.text = photos[indexPath.row].title ?? "No Description"
        cell.photoImageView.downloadImage(from: images[indexPath.row])
        return cell
    }
    let imageCache = NSCache<NSString,AnyObject>()
    
    extension UIImageView {
        
        func downloadImage(from urlString: String ) {
            guard let url = URL(string: urlString) else { return }
            storeCache(url: url)
        }
        
        func storeCache(url:URL){
            if let cachedImage = imageCache.object(forKey: url.absoluteString as NSString) as? UIImage {
                self.image = cachedImage
            }else {
                let _: Void = URLSession.shared.dataTask(with: url) { [weak self] data, response, error in
                    
                    guard let self = self else { return }
                    
    
                    if error != nil { return }
                    DispatchQueue.main.async {
                        if let downloadedImage = UIImage(data: data!) {
                            imageCache.setObject(downloadedImage, forKey: url.absoluteString as NSString)
                            self.image = downloadedImage
                        }
                    }
                }.resume()
            }
        }
        
    }