Swift

如果使用UIDatePicker时将模式设置为CountDownTimer，即可让该控件作为倒计时器来使用。效果图如下：

  

下面是代码示例：

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import UIKit   class ViewController: UIViewController {           var  ctimer:UIDatePicker!     var btnstart:UIButton!           var leftTime:Int = 180     var alertView:UIAlertView!           var timer:NSTimer!           override func viewDidLoad() {         super.viewDidLoad()         // Do any additional setup after loading the view, typically from a nib.                   ctimer = UIDatePicker(frame:CGRectMake(0.0, 120.0, 200.0, 200.0))         self.ctimer.datePickerMode = UIDatePickerMode.CountDownTimer;                   //必须为 60 的整数倍，比如设置为100，值自动变为 60         self.ctimer.countDownDuration = NSTimeInterval(leftTime);         ctimer.addTarget(self, action: "timerChanged", forControlEvents: UIControlEvents.ValueChanged)                   self.view.addSubview(ctimer)                   btnstart =  UIButton.buttonWithType(UIButtonType.System) as! UIButton         btnstart.frame = CGRect(x:100, y:400, 100, height:100);         btnstart.setTitleColor(UIColor.redColor(), forState: UIControlState.Normal)         btnstart.setTitleColor(UIColor.greenColor(), forState:UIControlState.Disabled)         btnstart.setTitle("开始", forState:UIControlState.Normal)         btnstart.setTitle("倒计时中", forState:UIControlState.Disabled)                   btnstart.clipsToBounds = true;         btnstart.layer.cornerRadius = 5;         btnstart.addTarget(self, action:"startClicked:",             forControlEvents:UIControlEvents.TouchUpInside)                   self.view.addSubview(btnstart)     }           func timerChanged()     {         println("倒计时：(self.ctimer.countDownDuration)")     }           /**     *开始倒计时按钮点击     */     func startClicked(sender:UIButton)     {         self.btnstart.enabled = false;                   // 获取该倒计时器的剩余时间         leftTime = Int(self.ctimer.countDownDuration);         // 禁用UIDatePicker控件和按钮         self.ctimer.enabled = false;                   // 创建一个UIAlertView对象（警告框），并确认，倒计时开始         alertView = UIAlertView()         alertView.title = "到计时开始"         alertView.message = "倒计时开始，还有 (leftTime) 秒..."         alertView.addButtonWithTitle("确定")         // 显示UIAlertView组件         alertView.show()         // 启用计时器，控制每秒执行一次tickDown方法         timer = NSTimer.scheduledTimerWithTimeInterval(NSTimeInterval(1),             target:self,selector:Selector("tickDown"),             userInfo:nil,repeats:true)     }           /**     *计时器每秒触发事件     **/     func tickDown()     {         alertView.message = "倒计时开始，还有 (leftTime) 秒..."         // 将剩余时间减少1秒         leftTime -= 1;         // 修改UIDatePicker的剩余时间         self.ctimer.countDownDuration = NSTimeInterval(leftTime);         println(leftTime)         // 如果剩余时间小于等于0         if(leftTime <= 0)         {             // 取消定时器             timer.invalidate();             // 启用UIDatePicker控件和按钮             self.ctimer.enabled = true;             self.btnstart.enabled = true;             alertView.message = "时间到！"         }     } }