在AppDelegate.swift中输入以下语句：
import UIKit
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
self.window = UIWindow(frame: UIScreen.main.bounds)
self.window?.backgroundColor = UIColor.white
self.window?.makeKeyAndVisible()
self.window?.rootViewController = UIViewController()
//redView
let redView = UIView(frame: CGRect(x: 107, y: 268, width: 200, height: 200))
redView.backgroundColor = UIColor.red
redView.tag = 200
self.window?.addSubview(redView)
redView.layer.cornerRadius = 100
//yellowView
let yellowView = UIView(frame: CGRect(x: 132, y:293, width: 150, height: 150))
yellowView.backgroundColor = UIColor.yellow
yellowView.tag = 201
self.window?.addSubview(yellowView)
yellowView.layer.cornerRadius = 75
//blueView
let blueView = UIView(frame: CGRect(x: 157, y: 318, width: 100, height: 100))
blueView.backgroundColor = UIColor.blue
blueView.tag = 202
self.window?.addSubview(blueView)
blueView.layer.cornerRadius = 50
//添加定时器
//参数1:定时执行的间隔
//参数2:目标对象
//参数3:目标对象执行的方法
//参数4:用户信息 nil
//参数5:定时器是否重复执行
Timer.scheduledTimer(timeInterval: 0.8, target: self, selector: #selector(changeColor), userInfo: nil, repeats: true)
return true
}
//MARK:定时器找到目标对象执行的方法
func changeColor() {
let redView = self.window?.viewWithTag(200)
//存储redView的背景颜色
let color = redView?.backgroundColor
self.window?.viewWithTag(200)?.backgroundColor = self.window?.viewWithTag(201)?.backgroundColor
self.window?.viewWithTag(201)?.backgroundColor = self.window?.viewWithTag(202)?.backgroundColor
self.window?.viewWithTag(202)?.backgroundColor = color
}
