如何像音乐播放器中那样设置倒数计时器？

Question

我有一个标签，其值为“ 03:48”。

我想像音乐播放器一样倒计时。我怎样才能做到这一点？

03:48 03:47 03:46 03:45 … 00:00

var musictime =3:48

func stringFromTimeInterval(interval: NSTimeInterval) -> String {
    let interval = Int(interval)
    let seconds = interval % 60
    let minutes = (interval / 60)      
    return String(format: "%02d:%02d", minutes, seconds)
}

func startTimer() {
    var duration=musictime.componentsSeparatedByString(":")   //split 3  and 48

    var count = duration[0].toInt()! * 60 + duration[1].toInt()! //224 second

    timerCounter = NSTimeInterval( count )
    NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: "onTimer:", userInfo: nil, repeats: true)
}

@objc func onTimer(timer:NSTimer!) {
    // Here is the string containing the timer
    // Update your label here
    //println(stringFromTimeInterval(timerCounter))
    statusLabel.text=stringFromTimeInterval(timerCounter)

    timerCounter!--
}

Answer 1

您应该看看NSDate属性timeIntervalSinceNow。您所需要做的就是使用NSDate方法dateByAddingTimeInterval将将来的日期设置为endDate
，如下所示：

class ViewController: UIViewController {

    @IBOutlet weak var timerLabel: UILabel!

    var remainingTime: NSTimeInterval = 0
    var endDate: NSDate!
    var timer = NSTimer()

    override func viewDidLoad() {
        super.viewDidLoad()
        remainingTime = 228.0   // choose as many seconds as you want (total time)
        endDate = NSDate().dateByAddingTimeInterval(remainingTime)   // set your future end date by adding the time for your timer

        timer = NSTimer.scheduledTimerWithTimeInterval(0.1, target: self, selector: "updateLabel", userInfo: nil, repeats: true)  // create a timer to update your label
    }
    func updateLabel() {
        timerLabel.text = endDate.timeIntervalSinceNow.mmss
    }
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

// you will need this extension to convert your time interval to a time string

extension NSTimeInterval {
    var mmss: String {
        return self < 0 ? "00:00" : String(format:"%02d:%02d", Int((self/60.0)%60), Int(self % 60))
    }
    var hmmss: String {
        return String(format:"%d:%02d:%02d", Int(self/3600.0), Int(self / 60.0 % 60), Int(self % 60))
    }
}