缓存后调整图像大小

Question

我的缓存照片有问题。首先，我从JSON更新tableView，并且图像很大： 屏幕截图：imageBeforeCache

但是在检查缓存后，图像会变小：imageAfterCache

代码：

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

        // 1
        let cell = tableView.dequeueReusableCell(withIdentifier: "GameCell", for: indexPath)
        let dictionary = self.tableData[(indexPath as NSIndexPath).row] as! [String:AnyObject]
        cell.textLabel!.text = dictionary["trackName"] as? String
        cell.imageView?.image = UIImage(named: "placeholder")

        if (self.cache.object(forKey: (indexPath as NSIndexPath).row as AnyObject) != nil){
            // 2
            // Use cache
            print("Cached image used, no need to download it")
            cell.imageView?.image = self.cache.object(forKey: (indexPath as NSIndexPath).row as AnyObject) as? UIImage
        }else{
            // 3
            let artworkUrl = dictionary["artworkUrl100"] as! String
            let url:URL! = URL(string: artworkUrl)
            task = session.downloadTask(with: url, completionHandler: { (location, response, error) -> Void in
                if let data = try? Data(contentsOf: url){
                    // 4
                    DispatchQueue.main.async(execute: { () -> Void in
                        // 5
                        // Before we assign the image, check whether the current cell is visible
                        if let updateCell = tableView.cellForRow(at: indexPath) {
                            let img:UIImage! = UIImage(data: data)
                            updateCell.imageView?.image = img
                            self.cache.setObject(img, forKey: (indexPath as NSIndexPath).row as AnyObject)
                        }
                    })
                }
            })
            task.resume()
        }
        return cell
    }

有什么想法吗？