ios - 快速激活停止后，秒表上的开始按钮会重置计时器

Question

为什么按下停止按钮后，秒表上的开始按钮会重置计时器？一切正常，直到我停止计时器然后重新启动它。它应该从停止的地方继续，但它会将计时器重置为 0。这是我的代码:

ViewController 类:UIViewController {

var timer = NSTimer()
var startTime = NSTimeInterval()

@IBOutlet var displayTimeLabel: UILabel!

@IBAction func start(sender: AnyObject) {

    if !timer.valid {

        timer = NSTimer.scheduledTimerWithTimeInterval(0.1, target: self, selector: #selector(ViewController.updateTime), userInfo: nil, repeats: true)

    }

    startTime = NSDate.timeIntervalSinceReferenceDate()

}

@IBAction func stop(sender: AnyObject) {

    timer.invalidate()
}

func updateTime() {

    let currentTime = NSDate.timeIntervalSinceReferenceDate()
    var elapsedTime: NSTimeInterval = currentTime - startTime

    let hours = UInt8(elapsedTime / 3600)
    elapsedTime -= (NSTimeInterval(hours) * 3600)

    let minutes = UInt8(elapsedTime / 60)
    elapsedTime -= (NSTimeInterval(minutes) * 60)

    let seconds = UInt8(elapsedTime)
    elapsedTime -= NSTimeInterval(seconds)

    let fraction = UInt8(elapsedTime * 100)

    let strHours = String(format: "%02d", hours)
    let strMinutes = String(format: "%02d", minutes)
    let strSeconds = String(format: "%02d", seconds)
    let strFraction = String(format: "%02d", fraction)

    displayTimeLabel.text = "\(strHours):\(strMinutes):\(strSeconds):\(strFraction)"

}

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
}

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

}

Answer 1

每次调用 start 方法时，您都会设置 startTime。您只想在第一次调用时执行此操作。您可以使用选项来正确确定状态，并且仅在 startTime 最初为零时设置它。

然后，您可以创建一个重置按钮，其函数只需设置 startDate = nil

class ViewController: UIViewController {

    var timer : NSTimer?
    var startTime? : NSTimeInterval?
    var accumulatedTime = NSTimeInterval()

    @IBOutlet var displayTimeLabel: UILabel!

    @IBAction func start(sender: AnyObject) {

        guard self.timer == nil else {
            return
        }

        self.startTime = NSDate.timeIntervalSinceReferenceDate()

        self.timer = NSTimer.scheduledTimerWithTimeInterval(0.1, target: self, selector: #selector(ViewController.updateTime), userInfo: nil, repeats: true)
    }

    @IBAction func stop(sender: AnyObject) {

        guard self.timer != nil else {
            return
        }

        self.timer!.invalidate()
        self.timer = nil
    }

    func updateTime() {

        let currentTime = NSDate.timeIntervalSinceReferenceDate()
        let intervalTime = currentTime - startTime!
        self.startTime = currentTime
        self.accumulatedTime += intervalTime

        var elapsedTime = self.accumulatedTime

        let hours = UInt8(elapsedTime / 3600)
        elapsedTime -= (NSTimeInterval(hours) * 3600)

        let minutes = UInt8(elapsedTime / 60)
        elapsedTime -= (NSTimeInterval(minutes) * 60)

        let seconds = UInt8(elapsedTime)
        elapsedTime -= NSTimeInterval(seconds)

        let fraction = UInt8(elapsedTime * 100)

        let timeString = String(format:"%02d:%02d:%02d.%02d",hours,minutes,seconds,fraction)
        displayTimeLabel.text = timeString

    }
}