func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        print(#function)
        print("当应用程序启动完成的时候,系统会自动调用代理这个方法")
        return true
    }

    func applicationWillResignActive(_ application: UIApplication) {
        // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
        // Use this method to pause ongoing tasks, disable timers, and invalidate graphics rendering callbacks. Games should use this method to pause the game.
        print(#function)
        print("当应用程序失去焦点的时候就会调用")
    }
    

    func applicationDidEnterBackground(_ application: UIApplication) {
        // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
        // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
        print(#function)
        print("当应用程序进入后台的时候就会调用")
    }

    func applicationWillEnterForeground(_ application: UIApplication) {
        // Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
        print(#function)
        print("当应用程序进入前台的时候就会调用")
    }

    func applicationDidBecomeActive(_ application: UIApplication) {
        // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
        print(#function)
        print("当应用程序获取焦点的时候就会调用")
    }

    func applicationWillTerminate(_ application: UIApplication) {
        // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
        print(#function)
        print("当应用程序关闭的时候就会调用")
    }

    func applicationDidReceiveMemoryWarning(_ application: UIApplication) {
        print(#function)
        print("监听内存警告")
    }

• 程序第一次启动

application(_:didFinishLaunchingWithOptions:)
当应用程序启动完成的时候,系统会自动调用代理这个方法
applicationDidBecomeActive
当应用程序获取焦点的时候就会调用

• 程序进入后台

applicationWillResignActive
当应用程序失去焦点的时候就会调用
applicationDidEnterBackground
当应用程序进入后台的时候就会调用

• 程序进入前台

applicationWillEnterForeground
当应用程序进入前台的时候就会调用
applicationDidBecomeActive
当应用程序获取焦点的时候就会调用