Question

我正在尝试通过'异步'从解析下载图像。

    override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath, object: PFObject?) -> PFTableViewCell? {

    var cell:CatsTableViewCell? = tableView.dequeueReusableCellWithIdentifier(cellIdentifier) as? CatsTableViewCell

    if(cell == nil) {
        cell = NSBundle.mainBundle().loadNibNamed("CatsTableViewCell", owner: self, options: nil) [0] as? CatsTableViewCell
    }

    if let pfObject = object {
        cell?.catNameLabel?.text = pfObject["name"] as? String

        var votes:Int? = pfObject["votes"] as? Int
        if votes == nil {
            votes = 0
        }
        cell?.catVotesLabel?.text = "\(votes!) votes"

        var credit:String? = pfObject["cc_by"] as? String
        if credit != nil {
            cell?.catCreditLabel?.text = "\(credit!) / CC 2.0"
        }
        cell?.catImageView?.image = nil

        if var urlString:String? = pfObject["url"] as? String {
            var url:NSURL? = NSURL(string: urlString!)

            if var url:NSURL? = NSURL(string: urlString!) {
                var error:NSError?
                var request:NSURLRequest = NSURLRequest(URL: url!, cachePolicy: NSURLRequestCachePolicy.ReturnCacheDataElseLoad, timeoutInterval: 5.0)

                NSOperationQueue.mainQueue().cancelAllOperations()

                NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue(), completionHandler: {
                    (response:NSURLResponse?, imageData:NSData?, error:NSError?) -> Void in

                    cell?.catImageView?.image = UIImage(data: imageData!)

                })
            }
        }

现在我改了几个代码

completionHandler: {
                    (response:NSURLResponse!, imageData:NSData!, error:NSError!) -> Void in

                    cell?.catImageView?.image = UIImage(data: imageData)

到

completionHandler: {
                    (response:NSURLResponse?, imageData:NSData?, error:NSError?) -> Void in

                    cell?.catImageView?.image = UIImage(data: imageData!)

并且没有严重错误，但图像未显示在模拟器上。任何帮助将是欣赏。谢谢大家。

- 第一个问题 -

*问题发生在下面 cell？.catImageView？.image = UIImage（data：imageData）它说

可选类型'（）的值？'未展开;你的意思是使用'！'还是'？'？*

Answer 1

初始化程序init（data :)返回一个可选的UIImage。您应该检查并打开它：

NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue(), completionHandler: {
(response: NSURLResponse?, imageData: NSData?, error: NSError?) -> Void in
    if let e = error {
        print(e)
        return
    }
    guard let data = imageData else { return }
    if let image = UIImage(data: data) {
        cell?.catImageView?.image = image
    }

})

从Parse异步下载图像

1 个答案: