iOS 生命周期

1. 启动后

   func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool
   
   func applicationDidBecomeActive(_ application: UIApplication)
   

2. 双击home键

   - (void)applicationWillResignActive:(UIApplication *)application
   

3. 双击home键后，点击home键回到app

func applicationDidBecomeActive(_ application: UIApplication)

4. 点击home键，app进入后台

func applicationWillResignActive(_ application: UIApplication)

func applicationDidEnterBackground(_ application: UIApplication)

5. 从后台返回到app

func applicationWillEnterForeground(_ application: UIApplication)

func applicationDidBecomeActive(_ application: UIApplication)

6. 当把app推出时，会调用

- (void)applicationWillTerminate:(UIApplication *)application