问如何在Swift游戏中创建2-3小时的前台和后台计时器？

EN

var coinCountdown = 10800 // 3hr = 10800
var coinCurrentTimer = NSTimer.init()
var coinCountdownLabel = SKLabelNode()

self.coinCurrentTimer = NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: #selector(GameScene.updateCoinCountdown), userInfo: nil, repeats: true)

func updateCoinCountdown() {
        if(self.coinCountdown > 0){
            var hour = String(self.coinCountdown / 3600)
            var minutes = String((self.coinCountdown % 3600) / 60)
            var seconds = String((self.coinCountdown % 3600) % 60)

            if Int(hour) < 10 {
                hour = "0" + hour
            }

            if Int(minutes) < 10 {
                minutes = "0" + minutes
            }

            if Int(seconds) < 10 {
                seconds = "0" + seconds
            }

            self.coinCountdownLabel.text = hour + ":" + minutes + ":" + seconds
            self.coinCountdown = self.coinCountdown - 1

            let defaults = NSUserDefaults.standardUserDefaults()
            if defaults.valueForKey("coinCountdown") != nil {
                defaults.setValue(self.coinCountdown, forKey: "coinCountdown")
            }

        }else{
            print("Done! Send notification and show get coin button")
        }
    }