UIDatePicker倒计时 swift

//
// ViewController.swift
// UILabelTest
//
// Created by mac on 15/6/23.
// Copyright (c) 2015年 fangyuhao. All rights reserved.
//

import UIKit

class ViewController: UIViewController{
var ctimer:UIDatePicker!
var btnstart:UIButton!
var leftTime:Int = 180
var timer:NSTimer!

override func viewDidLoad() {
    super.viewDidLoad()
   ctimer = UIDatePicker(frame: CGRectMake(0, 120.0, 200, 200))
    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)")
}
override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
}
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

    var message = NSString(format: "倒计时开始，还有%d秒", leftTime)

    let alertView = UIAlertView()
    alertView.title = "倒计时开始"
    alertView.message = message
    alertView.addButtonWithTitle("确定")
    alertView.show()
    //启动计时器，控制每隔60s执行一次tickDown方法
    timer = NSTimer.scheduledTimerWithTimeInterval(NSTimeInterval(1), target: self, selector: Selector("tickDown"), userInfo: nil, repeats: true)
}

func tickDown(){
    leftTime -= 1
    self.ctimer.countDownDuration = NSTimeInterval(leftTime)
    println(leftTime)
    if(leftTime<=0){
        timer.invalidate()
        self.ctimer.enabled = true
        self.btnstart.enabled = true

        let alertView = UIAlertView()
        alertView.title = "时间到"
        alertView.message = "时间到"
        alertView.addButtonWithTitle("确定")
        alertView.show()
    }
}

}