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Swift - 使用UIDatePicker实现倒计时功能

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：

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, width: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！"
        }
    }
}