ios - 加载图像使我的桌面 View 变慢

Question

我从 json url 获取数据，但是当我想加载图像时，速度非常慢!

class NewsTableViewController: UITableViewController {

    var ids             = [String]()
    var titles          = [String]()
    var descriptions    = [String]()
    var images          = [String]()
    var links           = [String]()
    var dates           = [String]()


    @IBOutlet var table_news: UITableView!

    override func viewDidLoad() {
        super.viewDidLoad()
        table_news.delegate = self
        getNews()

        // Uncomment the following line to preserve selection between presentations
        // self.clearsSelectionOnViewWillAppear = false

        // Uncomment the following line to display an Edit button in the navigation bar for this view controller.
        // self.navigationItem.rightBarButtonItem = self.editButtonItem()
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    // MARK: - Table view data source

    override func numberOfSections(in tableView: UITableView) -> Int {
        // #warning Incomplete implementation, return the number of sections
        return 1
    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        // #warning Incomplete implementation, return the number of rows
        return self.ids.count
    }


    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell:NewsTableViewCell = self.tableView.dequeueReusableCell(withIdentifier: "news_cell") as! NewsTableViewCell


        cell.lbl_date.text = self.dates[indexPath.row]
        cell.lbl_title.text = self.titles[indexPath.row]

        var des = self.descriptions[indexPath.row]

        if des.characters.count > 200 {
            let range =  des.rangeOfComposedCharacterSequences(for: des.startIndex..<des.index(des.startIndex, offsetBy: 200))
            let tmpValue = des.substring(with: range).appending("...")

            cell.lbl_des.text = tmpValue
        }


        DispatchQueue.main.async{
            cell.img_news.setImageFromURl(stringImageUrl: self.images[indexPath.row])

        }

        return cell
    }


    /*
    // Override to support conditional editing of the table view.
    override func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
        // Return false if you do not want the specified item to be editable.
        return true
    }
    */

    /*
    // Override to support editing the table view.
    override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCellEditingStyle, forRowAt indexPath: IndexPath) {
        if editingStyle == .delete {
            // Delete the row from the data source
            tableView.deleteRows(at: [indexPath], with: .fade)
        } else if editingStyle == .insert {
            // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view
        }    
    }
    */

    /*
    // Override to support rearranging the table view.
    override func tableView(_ tableView: UITableView, moveRowAt fromIndexPath: IndexPath, to: IndexPath) {

    }
    */

    /*
    // Override to support conditional rearranging of the table view.
    override func tableView(_ tableView: UITableView, canMoveRowAt indexPath: IndexPath) -> Bool {
        // Return false if you do not want the item to be re-orderable.
        return true
    }
    */

    /*
    // MARK: - Navigation

    // In a storyboard-based application, you will often want to do a little preparation before navigation
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        // Get the new view controller using segue.destinationViewController.
        // Pass the selected object to the new view controller.
    }
    */

    func getNews() {
        RestApiManager.sharedInstance.getNews { (json: JSON) in

            if let results = json.array {
                for entry in results {


                  self.ids.append(entry["id"].string!)
                  self.titles.append(entry["title"].string!)
                  self.descriptions.append(entry["description"].string!)
                  self.images.append(entry["images"].string!)
                  self.links.append(entry["link"].string!)
                  self.dates.append(entry["date"].string!)

                }



                DispatchQueue.main.async{
                    self.table_news.reloadData()
                }


            }

        }

    }

}

<小时/>

自定义单元格:

extension UIImageView{

    func setImageFromURl(stringImageUrl url: String){

        if let url = NSURL(string: url) {
            if let data = NSData(contentsOf: url as URL) {
                self.image = UIImage(data: data as Data)
            }
        }
    }
}
class NewsTableViewCell: UITableViewCell {



    @IBOutlet weak var img_news: UIImageView!
    @IBOutlet weak var lbl_title: UILabel!
    @IBOutlet weak var lbl_date: UILabel!
    @IBOutlet weak var lbl_des: UILabel!



    override func awakeFromNib() {
        super.awakeFromNib()
        // Initialization code

        lbl_des.lineBreakMode = .byWordWrapping // or NSLineBreakMode.ByWordWrapping
        lbl_des.numberOfLines = 0
    }

    override func setSelected(_ selected: Bool, animated: Bool) {
        super.setSelected(selected, animated: animated)

        // Configure the view for the selected state
    }

}

我正在使用扩展 ImageView 。

Answer 1

您提到的缓慢问题出在 UIImageView 扩展中

extension UIImageView{

    func setImageFromURl(stringImageUrl url: String){

        if let url = NSURL(string: url) {
            if let data = NSData(contentsOf: url as URL) {
                self.image = UIImage(data: data as Data)
            }
        }
    }
}

在 NSData(contentsOf: url as URL) 中，您将从网络同步检索 URL 的内容，从而阻塞主线程。您可以使用带有异步回调的 NSURLSession 或使用一些第 3 方库( SDWebImage 可能是最常用且经过测试的)来下载内容。