Question

我创建了一个带有自己的xib文件的自定义集合视图单元类。我希望显示一个倒计时运行计时器。

我有一个可以显示计时器的工作函数：

getObservable(arg){
   return combineLatest(of(arg), obs$).pipe(
     map(([arg, data]) => {})
   );
}

但是因为现在我在单元类中实现了这个函数，所以计时器不会运行。我在这里做错了吗？谢谢你们。

Answer 1

有几件事：

我不建议使用对计时器处理程序的调用
```
timeRemaining = timeRemaining - 1
```
我会保存nextRefreshTime并计算当前时间与nextRefreshTime之间经过的时间，以显示剩余时间。
注意，当您调用scheduledTimer时，会将其添加到运行循环中，因此您不必自己将其添加到运行循环中。

或者，如果您想在runloop上使用.commonModes以允许标签计时器在滚动期间继续，只需使用Timer创建init，然后将其添加到您的runloop

但将scheduleTimer和add再次用于您的运行循环是没有意义的。
我会忘记自己计算分钟数和秒数。您可以使用DateComponentsFormatter很好地显示剩余时间。
您谈到了在viewDidLoad启动计时器。但是UICollectionViewCell没有这样的方法（如果你创建一个这个名字，它就不会使用它）。相反，请调用一些方法在cellForItemAt中配置单元格。
模型对象（如下一次数据刷新时）不属于单元格。单元格是暂时的UIKit对象，当您滚动时它们会进出内存，所以它不应该跟踪它。您应该拥有自己的模型，视图控制器负责在呈现单元格时促进此信息与单元的通信：
- 最初使用nextRefreshTime配置单元格;和
- 在nextRefreshTime更改时发布一些通知。
然后细胞将：
- 将自己添加为该通知的观察者，更新其nextRefreshTime;
- 每当通知时，取消任何先前的“标签更新”计时器（如果有的话），并在必要时启动新计时器;
- 标签更新处理程序应更新标签

因此：

class ViewController: UIViewController {

    @IBOutlet weak var collectionView: UICollectionView!

    static let resetTimerNotification = Notification.Name("someuniqueidentifier")

    // this handles the data refreshes (or whatever), say every two minutes, or whatever

    private var nextRefreshTime: Date? {
        didSet {
            NotificationCenter.default.post(name: ViewController.resetTimerNotification, object: nextRefreshTime)
            refreshDataTimer?.invalidate()
            if let when = nextRefreshTime {
                refreshDataTimer = Timer.scheduledTimer(withTimeInterval: when.timeIntervalSince(Date()), repeats: false) { [weak self] _ in
                    print("timer fired")
                    self?.resetTimer() // presumably, defer this until after the data refresh is done
                }
            }
        }
    }

    private weak var refreshDataTimer: Timer?

    override func viewDidLoad() {
        super.viewDidLoad()

        collectionView?.register(UINib(nibName: "TimeRemainingCell", bundle: nil), forCellWithReuseIdentifier: "TimeRemaining")

        resetTimer()
    }

    @IBAction func didTapResetButton(_ sender: Any) {
        resetTimer()
    }

    private func resetTimer() {
        nextRefreshTime = Date().addingTimeInterval(120) // or however you want to do this
    }
}

extension ViewController: UICollectionViewDataSource {
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 1
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

        // lets imagine that cell 0 is the TimeRemainingCell

        if indexPath.item == 0 {
            let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "TimeRemaining", for: indexPath) as! TimeRemainingCell

            cell.configure(for: nextRefreshTime)

            return cell
        }

        ... configure other types of cells
    }
}

和

class TimeRemainingCell: UICollectionViewCell {
    // MARK: - Properties

    @IBOutlet weak var timeRemainingLabel: UILabel!

    private var nextRefreshTime: Date? {
        didSet {
            labelUpdateTimer?.invalidate()

            if nextRefreshTime != nil {
                let timer = Timer(fire: nextRefreshTime!, interval: 0, repeats: false) { [weak self] timer in
                    // note, if cell is deallocated for any reason, let's stop the timer

                    guard let strongSelf = self else {
                        timer.invalidate()
                        return
                    }

                    strongSelf.updateLabel()
                }
                RunLoop.current.add(timer, forMode: .commonModes)
                labelUpdateTimer = timer
            }
        }
    }

    private weak var labelUpdateTimer: Timer?

    /// Formatter for time remaining
    ///
    /// Note, this gets us out of manually calculating minutes and seconds remaining

    private static let formatter: DateComponentsFormatter = {
        let _formatter = DateComponentsFormatter()
        _formatter.unitsStyle = .positional
        _formatter.allowedUnits = [.minute, .second]
        _formatter.zeroFormattingBehavior = .pad
        return _formatter
    }()


    // MARK: - init/deinit methods

    override init(frame: CGRect) {
        super.init(frame: frame)

        addNotificationObserver()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)

        addNotificationObserver()
    }

    deinit {
        labelUpdateTimer?.invalidate()
    }

    // MARK: - Configuration methods

    /// Add notification observer

    private func addNotificationObserver() {
        NotificationCenter.default.addObserver(forName: ViewController.resetTimerNotification, object: nil, queue: .main) { [weak self] notification in
            self?.nextRefreshTime = notification.object as? Date
            self?.updateLabel()
        }
    }

    /// Configure the cell for your model object.
    ///
    /// Called by collectionView(_:cellForItemAt:).
    ///
    /// Also starts the refresh timer.
    ///
    /// - Parameter object: Your model object

    func configure(for nextRefreshTime: Date?) {
        self.nextRefreshTime = nextRefreshTime
    }

    // MARK: - Label updating

    private func updateLabel() {
        let now = Date()

        if let when = nextRefreshTime {
            timeRemainingLabel.text = TimeRemainingCell.formatter.string(from: now, to: when)
        } else {
            timeRemainingLabel.text = "No time remaining"
        }
    }
}

在自定义UIcollectionview单元格标签中显示计时器

1 个答案: