Swift3.0 GCD定时器的使用DEMO

//截止日期

let endDate = datePicker.date

//开始日期

let startDate = Date()

//时间间隔

let timeInterval:TimeInterval = endDate.timeIntervalSince(startDate)

iftimer == nil {

 //剩余时间

 var timeout = timeInterval

 iftimeout !=0{

 //创建全局队列

 let queue = DispatchQueue.global()

 //在全局队列下创建一个时间源

 timer = DispatchSource.makeTimerSource(flags: [], queue: queue)

 //设定循环的间隔是一秒,并且立即开始

 timer?.scheduleRepeating(wallDeadline: DispatchWallTime.now(), interval: .seconds(1))

 //时间源出发事件

 timer?.setEventHandler(handler: {

  //必须是当前日期往后的日期,在datePicker上也做了限制

  iftimeout <=0{

  self.timer?.cancel()

  self.timer = nil

  DispatchQueue.main.async(execute: {

   self.day.text ="00"

   self.hour.text ="00"

   self.minute.text ="00"

   self.second.text ="00"

  })

  }else{

  //计算剩余时间

  let days = Int(timeout) / (3600*24)

  ifdays ==0{

   self.day.text =""

  }

  let hours = (Int(timeout) - Int(days) *24*3600) /3600

  let minutes = (Int(timeout) - Int(days) *24*3600- Int(hours) *3600) /60

  let seconds = Int(timeout) - Int(days) *24*3600- Int(hours) *3600- Int(minutes) *60

  //主队列中刷新UI

  DispatchQueue.main.async(execute: {

   ifdays ==0{

   self.day.text ="0"

   }else{

   self.day.text ="\(days)"

   }

   ifhours<10{

   self.hour.text ="0"+"\(hours)"

   }else{

   self.hour.text ="\(hours)"

   }

   ifminutes<10{

   self.minute.text ="0"+"\(minutes)"

   }else{

   self.minute.text ="\(minutes)"

   }

   ifseconds<10{

   self.second.text ="0"+"\(seconds)"

   }else{

   self.second.text ="\(seconds)"

   }

  })

  timeout -=1

  }

 })

 //启动时间源

 timer?.resume()

 }

}