在Swift中添加和减去时间

Question

我用伪代码编写了一些这样的代码，因为我不知道它的语法。我想让timeLeftLabel.text反映在6个小时后，剩下多少小时，几分钟和几秒钟。我最大的问题是我不知道如何加减时间。谁能帮我？

var timer = NSTimer() 

func timerResults() { 
    let theDate = NSDate() 
    var endTime = theDate //+ 6 hours 
    let timeLeft = endTime //- theDate 
    timeLeftLabel.text = "\(timeLeft)" 
} 

@IBOutlet weak var timeLeftLabel: UILabel! 
@IBAction func IBbtnUpdateTap(sender: UIButton){ 

timer = NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: Selector("timerResults"), userInfo: nil, repeats: true) 

} 

Answer 1

假设你的部署目标是iOS的8.0或更高版本，您应该使用NSDateComponentsFormatter来格式化串。你想要这样的事情：

class MyViewController : UIViewController { 

    @IBOutlet weak var timeLeftLabel: UILabel! 

    var targetDate: NSDate? 
    var labelUpdateTimer: NSTimer? 
    var timeLeftFormatter: NSDateComponentsFormatter? 

    @IBAction func startTimerButtonWasTapped() { 
     targetDate = NSDate(timeIntervalSinceNow: 6 * 60 * 60) 
     labelUpdateTimer = NSTimer.scheduledTimerWithTimeInterval(1, 
      target: self, selector: "labelUpdateTimerDidFire:", userInfo: nil, repeats: true) 
     timeLeftFormatter = NSDateComponentsFormatter() 
     timeLeftFormatter?.unitsStyle = .Abbreviated // gives e.g. "1h 20m 34s" 
      // You might prefer .Positional, which gives e.g. "1:20:34" 
     timeLeftFormatter?.allowedUnits = [ .Hour, .Minute, .Second ] 

     labelUpdateTimerDidFire(labelUpdateTimer!) 
    } 

    @objc func labelUpdateTimerDidFire(timer: NSTimer) { 
     let now = NSDate() 
     timeLeftLabel.text = timeLeftFormatter!.stringFromDate(now, 
      toDate: targetDate!) 
     if now.compare(targetDate!) != NSComparisonResult.OrderedAscending { 
      print("times up!") 
      labelUpdateTimer?.invalidate() 
     } 
    } 

} 

Answer 2

这将加6时间：

let future = now.dateByAddingTimeInterval(3600*6) // 1 hour is 3600 seconds 

这将找到的差异：

let difference = future.timeIntervalSinceDate(now)