override func viewDidLoad() {
        super.viewDidLoad()
        //监听是否触发home键挂起程序.
        NotificationCenter.default.addObserver(self, selector: #selector(self.applicationWillResignActive), name: NSNotification.Name.UIApplicationWillResignActive, object: nil)
        ///监听是否重新进入程序程序.
        NotificationCenter.default.addObserver(self, selector: #selector(self.applicationDidBecomeActive), name: NSNotification.Name.UIApplicationDidBecomeActive, object: nil)
        ///监听是否被kill
        NotificationCenter.default.addObserver(self, selector: #selector(self.applicationWillTerminate), name: NSNotification.Name.UIApplicationWillTerminate, object: nil)
    }
    func applicationWillResignActive(){
        print("监听是否触发home键挂起程序.")
    }
    func applicationDidBecomeActive(){
        print("监听是否重新进入程序程序.")
    }
    func applicationWillTerminate(){
        print("监听是否进入后台或被kill")
    }