1，创建

//控制器        timer = Timer.scheduledTimer(timeInterval: 0.001, target: self, selector: #selector(FifteenthViewController.tickDown), userInfo: nil, repeats: true)

2，方法实现

func tickDown(){        let a = Int(arc4random()%255)+1         let b = Int(arc4random()%255)+1         let c = Int(arc4random()%255)+1         self.view.backgroundColor = UIColor.init(red: CGFloat(a/255), green: CGFloat(b/255), blue: CGFloat(c/255), alpha: 1.0)    }

3，终止定时器的方法

timer.invalidate()

 上面写了个随机颜色，时间调快一点，就成了屏幕快闪！