快速跳过秒和暂停的计时器倒计时

Question

我正在为我正在更新的应用程序制作倒计时组件。我终于让它工作了，但是当它在我的模拟器上或者当我通过手机运行它时，它会卡住并跳过几秒钟，有时会冻结我的屏幕并且不允许我更改视图等。这是我下面的代码。我很好奇为什么会这样。

提前谢谢你！

class CountdownViewController: UIViewController {

@IBOutlet weak var days: UILabel!
@IBOutlet weak var hours: UILabel!
@IBOutlet weak var minutes: UILabel!
@IBOutlet weak var seconds: UILabel!

var timer:NSTimer!

func reloadData(){
    self.viewDidLoad()
}

override func viewDidLoad() {
    super.viewDidLoad()

    self.timer = NSTimer(timeInterval: 0.5, target: self, selector: Selector("reloadData"), userInfo: nil, repeats: true)

    NSRunLoop.currentRunLoop().addTimer(self.timer, forMode: NSRunLoopCommonModes)

    self.canDisplayBannerAds = true

    // here we set the current date
    let date = NSDate()
    let calendar = NSCalendar.currentCalendar()
    let components = calendar.components(.CalendarUnitHour | .CalendarUnitMinute | .CalendarUnitMonth | .CalendarUnitYear | .CalendarUnitDay | .CalendarUnitSecond, fromDate: date)
    let hour = components.hour
    let minute = components.minute
    let month = components.month
    let year = components.year
    let day = components.day
    let second = components.second

    let currentDate = calendar.dateFromComponents(components)

    // here we set the due date. When the timer is supposed to finish

    let userCalendar = NSCalendar.currentCalendar()

    let electionDate = NSDateComponents()
    electionDate.year = 2016
    electionDate.month = 11
    electionDate.day = 08
    electionDate.hour = 00
    electionDate.minute = 00
    electionDate.second = 00
    let electionDay = userCalendar.dateFromComponents(electionDate)!


    // Here we compare the two dates
    electionDay.timeIntervalSinceDate(currentDate!)

    let dayCalendarUnit: NSCalendarUnit = (.CalendarUnitDay | .CalendarUnitHour | .CalendarUnitMinute | .CalendarUnitSecond)

    //here we change the seconds to hours,minutes and days
    let electionDayDifference = userCalendar.components(dayCalendarUnit, fromDate: currentDate!, toDate: electionDay,options: nil)

    //finally, here we set the variable to our remaining time
    var daysLeft = electionDayDifference.day
    var hoursLeft = electionDayDifference.hour
    var minutesLeft = electionDayDifference.minute
    var secondsLeft = electionDayDifference.second

    days.text = String(daysLeft)
    hours.text = String(hoursLeft)
    minutes.text = String(minutesLeft)
    seconds.text = String(secondsLeft)

}

Answer 1

您每 0.5 秒向 RunLoop 添加越来越多的计时器。而且它们都被同时触发，随着时间的推移导致性能下降。您需要将// here we set the current date 注释下方的所有代码移动到reloadData 函数并从那里删除self.viewDidLoad()，一切都应该没问题。您的计时器将只安排一次，并且每 0.5 秒重复调用一次reloadData（因为您使用repeats: true 参数创建了它）。

Answer 2

不要调用 viewDidLoad()

它是一种委托方法，由视图控制器调用（一次），指定用于设置一次。

将要在计时器触发后执行的代码放入自定义函数中。 无需反复创建定时器，将参数repeats设置为true会定期调用选择器。