UITableView中的Swift异步调用

最好的方法是什么 异步调用 加载 UIImage到文本视图 作为tableView中的NSTextAttachment?到目前为止,这是非常糟糕的工作。

我使用URL字符串在多个tableView单元格中加载单个图像。

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "cell")

    //Transform Data From ^ to load at the bottom
    tableView.transform = CGAffineTransform (scaleX: 1,y: -1);
    cell?.contentView.transform = CGAffineTransform (scaleX: 1,y: -1);
    cell?.accessoryView?.transform = CGAffineTransform (scaleX: 1,y: -1);

    let username = cell?.viewWithTag(1) as! UITextView
    username.text = messageArray[indexPath.row].username

    let message = cell?.viewWithTag(2) as! UITextView
    //message.text = messageArray[indexPath.row].message // delete later

    var test = messageArray[indexPath.row].uploadedPhotoUrl
    print(test ?? String.self)

    if(test != ""){
        // create an NSMutableAttributedString that we'll append everything to
        let fullString = NSMutableAttributedString(string: "")

        // create our NSTextAttachment
        let image1Attachment = NSTextAttachment()

        URLSession.shared.dataTask(with: NSURL(string: messageArray[indexPath.row].uploadedPhotoUrl)! as URL, completionHandler: { (data, response, error) -> Void in
            if error != nil {
                print(error ?? String())
                return
            }

            DispatchQueue.main.async(execute: { () -> Void in
                let image = UIImage(data: data!)
                image1Attachment.image = image

                //calculate new size.  (-20 because I want to have a litle space on the right of picture)
                let newImageWidth = (message.bounds.size.width - 20 )

                //resize this
                image1Attachment.bounds = CGRect.init(x: 0, y: 0, width: newImageWidth, height: 200)

                // wrap the attachment in its own attributed string so we can append it
                let image1String = NSAttributedString(attachment: image1Attachment)

                // add the NSTextAttachment wrapper to our full string, then add some more text.
                fullString.append(image1String)
                fullString.append(NSAttributedString(string: message.text))

                // draw the result in a label
                message.attributedText = fullString

                //message.textStorage.insert(image1String, at: message.selectedRange.location)

                message.textColor = .white

                test = ""
            })
        }).resume()
    }else {
        message.text = messageArray[indexPath.row].message
    }

    let timeStamp = cell?.viewWithTag(3) as! UILabel
    timeStamp.text = messageArray[indexPath.row].timeStamp

    let imageView = cell?.viewWithTag(4) as! UIImageView
    imageView.image = nil
    let urlString = messageArray[indexPath.row].photoUrl
    imageView.layer.cornerRadius = 10
    imageView.clipsToBounds = true

    //Load profile image(on cell) with URL & Alamofire Library
    let downloadURL = NSURL(string: urlString!)
    imageView.af_setImage(withURL: downloadURL! as URL)

    return cell!
}

当索引滚动(出现和消失)时,图像仍然滞后,并且没有完全加载