ios - TableView 数据滞后

Question

所以我遇到了一个问题

在几次重新加载/添加行后，表格 View 变慢(对滚动、点击的响应变慢)

---

因此，在用户登录后，该应用会下载 10 个 “WorldMessages”。它被加载到这个 TableView 中。

如果用户向下滚动，它会调用加载更多 10 个的函数:loadOlderOwnWorldMessages()

每个单元格都有一个tapGestureRecognizer + longPressGestureRecognizer

而且我不得不提一下，如果用户重新加载 tableView，那么它会清除数据并再次仅加载前 10 个 WorldMessages

---

问题

我不知道为什么，但是例如，如果我重新加载 tableView 50 次并且每次向下滚动一点或更多，tableView 就会变慢。

可能是因为点击/长按手势识别器或限制？

应用看起来像这样:

视频卡顿后:

https://www.youtube.com/watch?v=65NkjS-Kz3M

(如果我终止该应用程序并再次打开它，它会再次顺利运行，直到我重新加载它几次)

代码:

//这不是全部代码，我删除了很多不重要的行(比如重新加载函数等)

class ProfileViewController: UIViewController, UITableViewDelegate, UITableViewDataSource, UITabBarDelegate {

    // Classes
    let handleData = HandleData()
    let handleResponses = HandleResponses()
    let worldMessagesFunctions = WorldMessagesFunctions()
    let profileFunctions = ProfileFunctions()

    // View Objects
    @IBOutlet var tableView : UITableView!

    // Variables
    var userWorldMessages = [WorldMessage]()
    var lastContentOffsetY : CGFloat?

    var currentSelectedWorldMessageIndexPath : IndexPath?

    // Main Code
    override func viewDidLoad() {
        super.viewDidLoad()

        userWorldMessages = ownWorldMessages.shared.worldMessages
    }

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
       return userWorldMessages.count
    }
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "ProfileWorldMessageCell", for: indexPath) as! ProfileWorldMessageCell

        let worldMessage = userWorldMessages[indexPath.row]

        cell.worldMessageData = worldMessage

        cell.messageLabel.text = worldMessage.message

        if let image = UIImage(named: "bubble") {
            let h = image.size.height / 2
            let w = image.size.width / 2
            cell.bubbleImageView.image = image
                .resizableImage(withCapInsets:
                    UIEdgeInsetsMake(h, w, h, w),
                                resizingMode: .stretch).withRenderingMode(.alwaysTemplate)

            cell.bubbleImageView.tintColor = appColors.worldMessageBubble

        }

        let calendar = NSCalendar.current
        let date = Date(timeIntervalSince1970: Double(worldMessage.leftTime))
        let dateFormatter = DateFormatter()
        dateFormatter.locale = Locale(identifier: "en_US")
        var dateFormat = "yyyy MMM dd"
        if calendar.isDateInToday(date) {
            // Today
            dateFormat = "HH:mm"
            dateFormatter.string(from: date)
        } else if (calendar.date(byAdding: .weekOfYear, value: -1, to: Date())! < date){
            // This last 7 days
            dateFormat = "EEEE HH:mm"
        } else if (calendar.date(byAdding: .month, value: -12, to: Date())! < date){
            // This year
            dateFormat = "MMM dd"
        } else {
            dateFormat = "yyyy MMM dd"
        }
        dateFormatter.dateFormat = dateFormat
        let strDate = dateFormatter.string(from: date)

        cell.timeLabel.text = strDate

        cell.commentsButton.setTitle("\(worldMessage.comments!) comments", for: .normal)
        cell.likesButton.setTitle("\(worldMessage.likes!) likes", for: .normal)

        // tapped
        let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(bubbleTappedHandler))
        cell.bubbleButton.addGestureRecognizer(tapGestureRecognizer)
        cell.bubbleButton.isUserInteractionEnabled = true

        // long pressed
        let longPressGestureRecognizer = UILongPressGestureRecognizer(target: self, action: #selector(bubbleLongPressHandler))
        longPressGestureRecognizer.minimumPressDuration = 0.5
        cell.addGestureRecognizer(longPressGestureRecognizer)
        cell.isUserInteractionEnabled = true

        return cell
    }
    var cellHeights: [IndexPath : CGFloat] = [:]
    func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
        cellHeights[indexPath] = cell.frame.size.height

        if indexPath.row == UserWorldMessagesStore.shared.worldMessages.count - 1 && userWorldMessagesCanLoadMore == true {
            loadOlderOwnWorldMessages()
        }
    }
    func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
        return UITableViewAutomaticDimension
    }
    func tableView(_ tableView: UITableView, estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
        if cellHeights[indexPath] != nil {
            return CGFloat(Float(cellHeights[indexPath] ?? 0.0))
        }
        else {
            return UITableViewAutomaticDimension
        }
    }
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        if (lastContentOffsetY != nil){
            tableView.setContentOffset(CGPoint(x: 0, y: lastContentOffsetY!), animated: false)
        }
    }



    func loadOlderOwnWorldMessages(){
        profileFunctions.loadOlderOwnWorldMessages(startIndex: (userWorldMessages.count)) { response, newUserWorldMessages in
            if let response = response {
                if response.type == 1 {
                    DispatchQueue.main.async(execute: {() -> Void in
                        if newUserWorldMessages != nil {

                            var insertRows : [IndexPath] = []
                            var fromIndex = UserWorldMessagesStore.shared.worldMessages.count - 1
                            for worldMessage in newUserWorldMessages! {
                                UserWorldMessagesStore.shared.worldMessages.append(worldMessage)
                                insertRows.append(IndexPath(row: fromIndex, section: 1))
                                fromIndex += 1
                            }
                            self.userWorldMessages = UserWorldMessagesStore.shared.worldMessages

                            self.tableView.beginUpdates()
                            self.tableView.insertRows(at: insertRows, with: .automatic)
                            self.tableView.endUpdates()


                        }

                        })
                } else {
                    DispatchQueue.main.async(execute: {() -> Void in
                        self.handleResponses.displayError(title: response.title, message: response.message)
                    })
                }
            }
        }
    }

    @objc func bubbleTappedHandler(sender: UITapGestureRecognizer, should: Bool) {
        let touchPoint = sender.location(in: self.tableView)
        if let indexPath = tableView.indexPathForRow(at: touchPoint) {
            if indexPath == currentSelectedWorldMessageIndexPath {
                // it was already selected, so deselect it

                deselectCurrentSelectedWorldMessage()
            } else {
                // select new one, deselect old one if was selected

                if (currentSelectedWorldMessageIndexPath != nil){
                    deselectCurrentSelectedWorldMessage()
                }

                selectWorldMessage(indexPath: indexPath)
            }
        }
    }
    func selectWorldMessage(indexPath: IndexPath) {

        tableView.selectRow(at: indexPath, animated: true, scrollPosition: .none)
        currentSelectedWorldMessageIndexPath = indexPath

        if let cell = tableView.cellForRow(at: indexPath) as? ProfileWorldMessageCell {

            // Change some constraints
            cell.messageLabelTopConstraint.constant = 14
            cell.messageLabelBottomConstraint.constant = 14
            UIView.animate(withDuration: 0.15, animations: {
                self.view.layoutIfNeeded()
                self.tableView.beginUpdates()
                self.tableView.endUpdates()
            }, completion: nil)
        }
    }
    @objc func deselectCurrentSelectedWorldMessage(){
        UIMenuController.shared.setMenuVisible(false, animated: true)
        if (currentSelectedWorldMessageIndexPath == nil){
            return
        }
        let indexPath = currentSelectedWorldMessageIndexPath!

        if let cell = tableView.cellForRow(at: indexPath) as? ProfileWorldMessageCell {

            // Change back some constraints
            cell.messageLabelTopConstraint.constant = 10
            cell.messageLabelBottomConstraint.constant = 10
            UIView.animate(withDuration: 0.15, animations: {
                self.view.layoutIfNeeded()
                self.tableView.beginUpdates()
                self.tableView.endUpdates()
            }, completion: nil)
        }

        currentSelectedWorldMessageIndexPath = nil
    }

    @objc func bubbleLongPressHandler(sender: UILongPressGestureRecognizer, should: Bool) {
        // Show options like copy, delete etc.
    }



}

Answer 1

您的 cellForRow 函数有几处非常错误:

• 细胞被重复使用，而您忽略了这一事实。每次调用 cellForRow 时，您都在创建手势识别器的新实例，而当单元格被重用时，您又添加了一个。这意味着如果你的单元格被重复使用了 50 次，它将添加 50 个手势识别器。您应该只创建一次手势识别器
• 您每次创建一个DateFormatter 并设置其dateFormat 属性，这实际上是一个非常昂贵的过程。相反，您应该为每种日期格式都有一个格式化程序的静态实例