tableView 中几个 NSTimer 对象的问题

Question

I have a TableView where each cell consists of a NSTimer object.

I have managed to make it work where I can run several timers, update them or delete them. But problem arises when I delete a running timer,

when I do that the next object in my list of Counters (timer objects) replaces this one, but the UILabel that is related to that is still referring to the old index and therefore the UI doesn't get updated any more.

At this point I'm really stuck, should I invalidate all timers and fire() them again after deleting one or is there a better way to do so?

ViewController Class (main issue is at "playPauseCounter" function)

import UIKit
import RealmSwift

class TimerController: UITableViewController, editDataDelegate, settingVCDelegate {

    // MARK: - Properties

    // delegate objects
    var timerArray: [String: Timer]?
    var counterArray: Results<Counter>?
    var counter: Counter?
    var index: String?


    var counters: Results<Counter>?
    var timerDict = [String: Timer]()

    private let reuseIdentifier = "TimerCell"
    private let cellSpacingHeight: CGFloat = 10
    var shared = DatabaseService.shared
    var sharedNotif = NotifService.shared

    // MARK: - Initializers
    override func viewDidLoad() {
        super.viewDidLoad()
        configureNavigationBar()
        tableView.register(TimerCell.self, forCellReuseIdentifier: reuseIdentifier)
//        How to handle when application goes to background and then comes to foreground
        NotificationCenter.default.addObserver(self, selector: #selector(pauseWhenBackground(noti:)), name: UIApplication.didEnterBackgroundNotification, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(continueWhenForeground(noti:)), name: UIApplication.willEnterForegroundNotification, object: nil)
        sharedNotif.requestLocalNotification()
        if shared.getCurrentTheme() == true {
            overrideUserInterfaceStyle = .dark
        } else {
            overrideUserInterfaceStyle = .light
        }
        refreshData()
    }

    override func viewDidAppear(_ animated: Bool) {
        refreshData()
        if shared.getCurrentTheme() == true {
            overrideUserInterfaceStyle = .dark
        } else {
            overrideUserInterfaceStyle = .light
        }
        tableView.reloadData()
    }

    // MARK: - UITableView Functions
    override func tableView(_ tableView: UITableView, trailingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
        let action = UIContextualAction(style: .normal, title: "Delete") { (_, _, completion) in
            guard let counter = self.counters?[indexPath.section] else { return }
            self.sharedNotif.removeLocalNotificationPending(id: counter.id)
            if let t = self.timerDict[counter.id] {
                t.invalidate()
            }
            self.shared.delete(idx: indexPath.section)
            self.tableView.reloadData()
            completion(true)
        }
        action.image = #imageLiteral(resourceName: "delete")
        action.backgroundColor = .textRed()
        return UISwipeActionsConfiguration(actions: [action])
    }

    override func tableView(_ tableView: UITableView, leadingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
        let edit = handleEdit(at: indexPath)
        return UISwipeActionsConfiguration(actions: [edit])
    }

    override func numberOfSections(in tableView: UITableView) -> Int {
        counters = shared.fetchAllCounters()
        guard let counters = counters else { return 0 } // later here load items from the database
        return counters.count
    }

    // There is just one row in every section
    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return 1
    }

    // Set the spacing between sections
    override func tableView(_ tableView: UITableView, heightForHeaderInSection section: Int) -> CGFloat {
        return cellSpacingHeight
    }

    override func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
        return 80
    }

    // Make the background color show through
    override func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
        let headerView = UIView()
        headerView.backgroundColor = UIColor.clear
        return headerView
    }
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

        // swiftlint:disable force_cast
        let cell = tableView.dequeueReusableCell(withIdentifier: reuseIdentifier, for: indexPath) as! TimerCell
        // swiftlint:enabl1e force_cast
        if let counters = counters {
            cell.counter = counters[indexPath.section]
            changeColorsLight(cell: cell, mode: counters[indexPath.section].counterMode)
        }
        cell.delegate = self
        return cell
    }
    func footerAddButton() {
        let footerView = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
        let btn = UIButton(type: .roundedRect)
        btn.setTitle("ADD", for: .normal)
        btn.setTitleColor(.black, for: .normal)
        btn.titleLabel?.font = UIFont.boldSystemFont(ofSize: 16)
        btn.translatesAutoresizingMaskIntoConstraints = false
        btn.layer.cornerRadius = 5
        btn.frame = CGRect(x: 0, y: 0, width: 50, height: 50)
        footerView.addSubview(btn)
        tableView.tableFooterView = footerView
    }

    //MARK: - Helper Methods
    func refreshData() {
        counters = shared.fetchAllCounters()
        if let counters = counters {
            for counter in counters where timerDict[counter.id] == nil {
                timerDict[counter.id] = Timer()
            }
        }
    }

    func getTimeDifference(_ startDate: Date) -> Int {
        let calendar = Calendar.current
        let components = calendar.dateComponents([.second], from: startDate, to: Date())
        if let secs = components.second {
            return abs(secs)
        }
        return 0
    }

    func configureNavigationBar() {
        navigationController?.navigationBar.barTintColor = UIColor.systemGray
        navigationController?.navigationBar.isTranslucent = false
        navigationItem.title = "Timers"
        navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Settings", style: .done, target: self, action: #selector(goToSettings))
        navigationItem.leftBarButtonItem = UIBarButtonItem(title: "Add", style: .done, target: self, action: #selector(goToNewTimer))
    }

    //MARK: - Event Handlers
    @objc func pauseWhenBackground(noti: Notification) {
        counters = shared.fetchAllCounters()
        guard let counters = counters else { return }
        for counter in counters where counter.counterMode == Mode.running.rawValue {
            guard let idx = counters.index(of: counter) else { return }
            shared.editCounter(idx: counter.id, name: nil, ot: nil, ct: nil, md: nil, timer: Date())
        }
    }

    @objc func continueWhenForeground(noti: Notification) {
        counters = shared.fetchAllCounters()
        guard let counters = counters else { return }
        for counter in counters where counter.counterMode == Mode.running.rawValue {
            if let savedDate = counter.savedTime {
                let diff = getTimeDifference(savedDate)
                if diff > 0 {
                    guard let idx = counters.index(of: counter) else { return }
                    shared.editCounter(idx: counter.id, name: nil, ot: nil, ct: counter.currentTime - diff, md: nil, timer: nil)
                }
            }
        }
    }

    @objc func goToSettings() {
        let settingVC = SettingController()
        settingVC.delegateVC = self
        timerArray = timerDict
        counterArray = shared.fetchAllCounters()
        navigationController?.pushViewController(settingVC, animated: true)
    }

    @objc func goToNewTimer() {
        let newTimerVC = TimeController()
        navigationController?.pushViewController(newTimerVC, animated: true)
    }

    func handleEdit(at indexPath: IndexPath) -> UIContextualAction {
        let action = UIContextualAction(style: .normal, title: "Edit") { (_, _, _) in
            let vc = TimeController()
            vc.delegate = self
            self.counter = self.counters![indexPath.section]
            self.index = self.counters![indexPath.section].id
            self.navigationController?.pushViewController(vc, animated: true)
        }
        action.image = #imageLiteral(resourceName: "edit")
        action.backgroundColor = .rgb(red: 239, blue: 13, green: 155)
        return action
    }
}

extension TimerController: CounterDelegate {

    // transfer seconds to h/m/s
    func updateCounterView(seconds: Int) -> String {
        let arr = secondsToDate(seconds: seconds)
        return String(format: "%02i:%02i:%02i", arr[0], arr[1], arr[2])
    }

    func playPauseCounter(cell: TimerCell) {
        let idx = self.tableView.indexPath(for: cell)
        guard let index = idx?.section else { return }
        guard let counter = counters?[index] else { return }
        let timeLabel = cell.timeLabel

        if counter.counterMode == Mode.notStarted.rawValue ||  counter.counterMode == Mode.paused.rawValue {
            changeColorsLight(cell: cell, mode: Mode.running.rawValue)
            // add local notification when user resumes or starts the timer
            sharedNotif.addLocalNotificationAlert(id: counter.id, name: counter.name, seconds: counter.currentTime)

            cell.backgroundColor = UIColor.rgb(red: 1, blue: 255, green: 123)
            shared.editCounter(idx: counter.id, name: nil, ot: nil, ct: nil, md: .running, timer: nil)
            timerDict[counter.id] = Timer.scheduledTimer(withTimeInterval: 1, repeats: true, block: { [weak self] (_) in
                if counter.currentTime > 0 {
                    print(counter.currentTime)
                    self?.shared.editCounter(idx: counter.id, name: nil, ot: nil, ct: counter.currentTime-1, md: nil, timer: nil)
                    timeLabel.text = self?.updateCounterView(seconds: counter.currentTime)
                } else if counter.currentTime == 0 {
                    // remove all delivered local notifications left
                    changeColorsLight(cell: cell, mode: Mode.ended.rawValue)
                    self?.sharedNotif.removeLocalNotificationsDelivered()
                    self?.timerDict[counter.id]!.invalidate()
                    self?.shared.editCounter(idx: counter.id, name: nil, ot: nil, ct: counter.currentTime, md: .ended, timer: nil)
                }
            })
            RunLoop.current.add(timerDict[counter.id]!, forMode: .common)
            timerDict[counter.id]!.tolerance = 0.15
        } else if counter.counterMode == Mode.running.rawValue {
            changeColorsLight(cell: cell, mode: Mode.paused.rawValue)
            sharedNotif.removeLocalNotificationPending(id: counter.id)
            timerDict[counter.id]!.invalidate()
            shared.editCounter(idx: counter.id, name: nil, ot: nil, ct: counter.currentTime, md: .paused, timer: nil)
        }
    }
    func resetCounter(cell: TimerCell) {
        let idx = self.tableView.indexPath(for: cell)
        guard let index = idx?.section else { return }
        guard let counter = counters?[index] else { return }
        timerDict[counter.id]!.invalidate()
        // remove the previous notification (if exists) before resetting the timer
        sharedNotif.removeLocalNotificationPending(id: counter.id)
        // change currentTime back to original
        shared.editCounter(idx: counter.id, name: nil, ot: nil, ct: counter.originalTime, md: .notStarted, timer: nil)
        cell.timeLabel.text = String(counter.originalTime)
        changeColorsLight(cell: cell, mode: Mode.notStarted.rawValue)
    }
}

model class

import Foundation
import RealmSwift

class Counter: Object {
    @objc dynamic var id: String = UUID().uuidString
    @objc dynamic var name: String = ""
    @objc dynamic var originalTime: Int = 0
    @objc dynamic var currentTime: Int = 0
    // Realm database doesnt work properly with objects of type enum
    @objc dynamic var counterMode: Int = 0
    @objc dynamic var savedTime: Date?
}

Answer 1

For anyone coming to this question in the future, I used the hint suggested by Paulw11 and created only one timer, and instead of saving indexes manually inside an array, saved all the current cells in the tableView each time the cellForRowAt function gets called.

here is the modified code for my solution:

import UIKit
import RealmSwift

class TimerController: UITableViewController, editDataDelegate, settingVCDelegate {

    // MARK: - Properties

    // delegate objects
    var timerArray: [String: Timer]?
    var counterArray: Results<Counter>?
    var counter: Counter?
    var index: String?

    var counters: Results<Counter>?
    var timer = Timer()
    var currentRunning = [TimerCell]()

    private let reuseIdentifier = "TimerCell"
    private let cellSpacingHeight: CGFloat = 10
    var shared = DatabaseService.shared
    var sharedNotif = NotifService.shared

    // MARK: - Initializers
    override func viewDidLoad() {
        super.viewDidLoad()
        shared.deleteAll()

        configureNavigationBar()

        tableView.register(TimerCell.self, forCellReuseIdentifier: reuseIdentifier)

        // How to handle when application goes to background and then comes to foreground
        NotificationCenter.default.addObserver(self, selector: #selector(pauseWhenBackground(noti:)), name: UIApplication.didEnterBackgroundNotification, object: nil)

        NotificationCenter.default.addObserver(self, selector: #selector(continueWhenForeground(noti:)), name: UIApplication.willEnterForegroundNotification, object: nil)

        sharedNotif.requestLocalNotification()

        if shared.getCurrentTheme() == true {
            overrideUserInterfaceStyle = .dark
        } else {
            overrideUserInterfaceStyle = .light
        }
        counters = shared.fetchAllCounters()

        // add this feature so timer will continue working when user drags down the list, and add tolerance to timer
        fireTimer()
    }

    override func viewDidAppear(_ animated: Bool) {
        counters = shared.fetchAllCounters()

        if shared.getCurrentTheme() == true {
            overrideUserInterfaceStyle = .dark
        } else {
            overrideUserInterfaceStyle = .light
        }
        tableView.reloadData()
    }

    // MARK: - UITableView Functions
    override func tableView(_ tableView: UITableView, trailingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
        let action = UIContextualAction(style: .normal, title: "Delete") { (_, _, completion) in
            guard let counter = self.counters?[indexPath.section] else { return }
            self.sharedNotif.removeLocalNotificationPending(id: counter.id)
            /////////////
            self.shared.delete(idx: indexPath.section)
            self.tableView.reloadData()
            ///////////
            completion(true)
        }
        action.image = #imageLiteral(resourceName: "delete")
        action.backgroundColor = .textRed()
        return UISwipeActionsConfiguration(actions: [action])
    }

    override func tableView(_ tableView: UITableView, leadingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
        let edit = handleEdit(at: indexPath)
        return UISwipeActionsConfiguration(actions: [edit])
    }

    override func numberOfSections(in tableView: UITableView) -> Int {
        print(currentRunning)
        currentRunning = []
        counters = shared.fetchAllCounters()
        guard let counters = counters else { return 0 } // later here load items from the database
        return counters.count
    }

    // There is just one row in every section
    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return 1
    }

    // Set the spacing between sections
    override func tableView(_ tableView: UITableView, heightForHeaderInSection section: Int) -> CGFloat {
        return cellSpacingHeight
    }

    override func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
        return 80
    }

    // Make the background color show through
    override func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
        let headerView = UIView()
        headerView.backgroundColor = UIColor.clear
        return headerView
    }
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

        // swiftlint:disable force_cast
        let cell = tableView.dequeueReusableCell(withIdentifier: reuseIdentifier, for: indexPath) as! TimerCell
        // swiftlint:enabl1e force_cast
        if let counters = counters {
            cell.counter = counters[indexPath.section]
            changeColorsLight(cell: cell, mode: counters[indexPath.section].counterMode)
            if cell.counter?.counterMode == Mode.running.rawValue {
                currentRunning.append(cell)
            }
        }
        cell.delegate = self
        return cell
    }
    func footerAddButton() {
        let footerView = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
        let btn = UIButton(type: .roundedRect)
        btn.setTitle("ADD", for: .normal)
        btn.setTitleColor(.black, for: .normal)
        btn.titleLabel?.font = UIFont.boldSystemFont(ofSize: 16)
        btn.translatesAutoresizingMaskIntoConstraints = false
        btn.layer.cornerRadius = 5
        btn.frame = CGRect(x: 0, y: 0, width: 50, height: 50)
        footerView.addSubview(btn)
        tableView.tableFooterView = footerView
    }

    //MARK: - Helper Methods
    func getTimeDifference(_ startDate: Date) -> Int {
        let calendar = Calendar.current
        let components = calendar.dateComponents([.second], from: startDate, to: Date())
        if let secs = components.second {
            return abs(secs)
        }
        return 0
    }

    func configureNavigationBar() {
        navigationController?.navigationBar.barTintColor = UIColor.systemGray
        navigationController?.navigationBar.isTranslucent = false
        navigationItem.title = "Timers"
        navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Settings", style: .done, target: self, action: #selector(goToSettings))
        navigationItem.leftBarButtonItem = UIBarButtonItem(title: "Add", style: .done, target: self, action: #selector(goToNewTimer))
    }

    //MARK: - Event Handlers
    @objc func pauseWhenBackground(noti: Notification) {
        counters = shared.fetchAllCounters()
        guard let counters = counters else { return }
        for counter in counters where counter.counterMode == Mode.running.rawValue {
            guard let idx = counters.index(of: counter) else { return }
            shared.editCounter(idx: counter.id, name: nil, ot: nil, ct: nil, md: nil, timer: Date())
        }
    }

    @objc func continueWhenForeground(noti: Notification) {
        counters = shared.fetchAllCounters()
        guard let counters = counters else { return }
        for counter in counters where counter.counterMode == Mode.running.rawValue {
            if let savedDate = counter.savedTime {
                let diff = getTimeDifference(savedDate)
                if diff > 0 {
                    guard let idx = counters.index(of: counter) else { return }
                    shared.editCounter(idx: counter.id, name: nil, ot: nil, ct: counter.currentTime - diff, md: nil, timer: nil)
                }
            }
        }
    }

    @objc func goToSettings() {
        let settingVC = SettingController()
        settingVC.delegateVC = self

        //////////////
        timerArray = [String: Timer]()
        /////////////

        counterArray = shared.fetchAllCounters()
        navigationController?.pushViewController(settingVC, animated: true)
    }

    @objc func goToNewTimer() {
        let newTimerVC = TimeController()
        navigationController?.pushViewController(newTimerVC, animated: true)
    }

    func handleEdit(at indexPath: IndexPath) -> UIContextualAction {
        let action = UIContextualAction(style: .normal, title: "Edit") { (_, _, _) in
            let vc = TimeController()
            vc.delegate = self
            self.counter = self.counters![indexPath.section]
            self.index = self.counters![indexPath.section].id
            self.navigationController?.pushViewController(vc, animated: true)
        }
        action.image = #imageLiteral(resourceName: "edit")
        action.backgroundColor = .rgb(red: 239, blue: 13, green: 155)
        return action
    }
}

extension TimerController: CounterDelegate {

    // transfer seconds to h/m/s
    func updateCounterView(seconds: Int) -> String {
        let arr = secondsToDate(seconds: seconds)
        return String(format: "%02i:%02i:%02i", arr[0], arr[1], arr[2])
    }

    func playPauseCounter(cell: TimerCell) {
        let idx = self.tableView.indexPath(for: cell)
        guard let index = idx?.section else { return }
        guard let counter = counters?[index] else { return }
        let timeLabel = cell.timeLabel

        if counter.counterMode == Mode.notStarted.rawValue ||  counter.counterMode == Mode.paused.rawValue {
            changeColorsLight(cell: cell, mode: Mode.running.rawValue)
            sharedNotif.addLocalNotificationAlert(id: counter.id, name: counter.name, seconds: counter.currentTime)
            cell.backgroundColor = UIColor.rgb(red: 1, blue: 255, green: 123)
            shared.editCounter(idx: counter.id, name: nil, ot: nil, ct: nil, md: .running, timer: nil)
            ///////////////
            currentRunning.append(cell)
            /////////////
        } else if counter.counterMode == Mode.running.rawValue {
            changeColorsLight(cell: cell, mode: Mode.paused.rawValue)
            sharedNotif.removeLocalNotificationPending(id: counter.id)
            shared.editCounter(idx: counter.id, name: nil, ot: nil, ct: counter.currentTime, md: .paused, timer: nil)
            ////////////////////
            guard let indexOf = currentRunning.index(of: cell) else { return }
            currentRunning.remove(at: indexOf)
            ///////////////
        }
    }

    func fireTimer() {
        timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true, block: { (_) in
            // for each item in the current running list, update it and save it to database
            for cell in self.currentRunning {
                guard let counter = cell.counter else { return }
                let timeLabel = cell.timeLabel
                if counter.currentTime > 0 {
                    self.shared.editCounter(idx: counter.id, name: nil, ot: nil, ct: counter.currentTime-1, md: nil, timer: nil)
                    timeLabel.text = self.updateCounterView(seconds: counter.currentTime)
                } else if counter.currentTime == 0 {
                    // remove all delivered local notifications left
//                    changeColorsLight(cell: cell, mode: Mode.ended.rawValue)
                    self.sharedNotif.removeLocalNotificationsDelivered()
                    self.shared.editCounter(idx: counter.id, name: nil, ot: nil, ct: counter.currentTime, md: .ended, timer: nil)
                    // here remove this item from the list
                    guard let indexOf = self.currentRunning.index(of: cell) else { return }
                    self.currentRunning.remove(at: indexOf)
                    ///////////////
                }
            }
        })
        RunLoop.current.add(timer, forMode: .common)
        timer.tolerance = 0.15
    }


    func resetCounter(cell: TimerCell) {
        let idx = self.tableView.indexPath(for: cell)
        guard let index = idx?.section else { return }
        guard let counter = counters?[index] else { return }

        // remove this index from the running list
        guard let indexOf = self.currentRunning.index(of: cell) else { return }
        self.currentRunning.remove(at: indexOf)
        //////////

        sharedNotif.removeLocalNotificationPending(id: counter.id)
        shared.editCounter(idx: counter.id, name: nil, ot: nil, ct: counter.originalTime, md: .notStarted, timer: nil)
        cell.timeLabel.text = String(counter.originalTime)
        changeColorsLight(cell: cell, mode: Mode.notStarted.rawValue)
    }
}