swift 应用进入前后台状态监听

//设置状态监听
    override func viewDidLoad() {
        super.viewDidLoad()
        NotificationCenter.default.addObserver(self, selector: #selector(appWillEnterForeground), name: UIApplication.willEnterForegroundNotification, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(appDidEnterBackground), name: UIApplication.didEnterBackgroundNotification, object: nil)
    }

    // 将进入前台通知
    @objc func appWillEnterForeground(){
        print("周期 ---将进入前台通知")
    }
    //应用程序确实进入了后台
    @objc func appDidEnterBackground(){
        print("周期 ---应用程序确实进入了后台")
    }