Swift - 异步加载各网站的favicon图标，并在单元格中显示

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import UIKit

class FaviconTableViewCell: UITableViewCell {

    //此操作队列运行下载的完成处理器

   // var operationQueue:NSOperationQueue?

    //此单元格显示的URL

    var url:NSURL? {

        //当URL发生变化

        didSet {

            //显示此文本

            self.textLabel?.text = self.url?.host

            //创建请求

            let request = NSURLRequest(URL: self.url!)

            let session = NSURLSession.sharedSession()

            let dataTask = session.dataTaskWithRequest(request,

                completionHandler: {(data, response, error) -> Void in

                    //将获取到的数据转化成图像

                    let image = UIImage(data: data!)

                    //对UI的更新必须在主队列上完成

                    NSOperationQueue.mainQueue().addOperationWithBlock({

                        () -> Void in

                        //将已加载的图像赋予图像视图

                        self.imageView?.image = image

                        //图像视图可能已经因为新图像而改变了尺寸

                        //所以需要重新调整单元格的布局

                        self.setNeedsLayout()

                    })

            }) as NSURLSessionTask

            //使用resume方法启动任务

            dataTask.resume()

        }

    }

    override func awakeFromNib() {

        super.awakeFromNib()

    }

    override func setSelected(selected: Bool, animated: Bool) {

        super.setSelected(selected, animated: animated)

    }

}

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import UIKit

class ViewController: UIViewController {

    let hosts = ["hangge.com","163.com","baidu.com","qq.com","taobao.com"]

    override func viewDidLoad() {

        super.viewDidLoad()

    }

    //在本例中，只有一个分区

    func numberOfSectionsInTableView(tableView: UITableView!) -> Int {

        return 1;

    }

    //返回表格行数（也就是返回控件数）

    func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

        return self.hosts.count

    }

    //创建各单元显示内容(创建参数indexPath指定的单元）

    func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath)

        -> UITableViewCell

    {

        //为了提供表格显示性能，已创建完成的单元需重复使用

        let identify:String = "FaviconCell"

        //同一形式的单元格重复使用，在声明时已注册

        let cell = tableView.dequeueReusableCellWithIdentifier(identify)

            as! FaviconTableViewCell

        let host = hosts[indexPath.row]

        let url = NSURL(string: "http://\(host)/favicon.ico")

        cell.url = url

        return cell

    }

    override func didReceiveMemoryWarning() {

        super.didReceiveMemoryWarning()

    }

}