iOS13中appdelegate的职责发现了改变： iOS13之前，Appdelegate的职责全权处理App生命周期和UI生命周期； iOS13之后，Appdelegate的职责是： 1、处理 App 生命周期 2、新的 Scene Session 生命周期 那UI的生命周期交给新增的Scene Delegate处理 - (void)scene:(UIScene *)scene willConnectToSession:(UISceneSession *)session options:(UISceneConnectionOptions *)connectionOptions { // Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`. // If using a storyboard, the `window` property will automatically be initialized and attached to the scene. // This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead). UIWindowScene *windowScene = (UIWindowScene *)scene; self.window = [[UIWindow alloc] initWithWindowScene:windowScene]; self.window.frame = windowScene.coordinateSpace.bounds; UITabBarController *tabbarController = [[UITabBarController alloc] init]; UIViewController *controller1 = [[UIViewController alloc] init]; controller1.view.backgroundColor = [UIColor redColor]; controller1.tabBarItem.title = @"新闻"; UIViewController *controller2 = [[UIViewController alloc] init]; controller2.view.backgroundColor = [UIColor yellowColor]; controller2.tabBarItem.title = @"视频"; UIViewController *controller3 = [[UIViewController alloc] init]; controller3.view.backgroundColor = [UIColor blueColor]; controller3.tabBarItem.title = @"推荐"; UIViewController *controller4 = [[UIViewController alloc] init]; controller4.view.backgroundColor = [UIColor greenColor]; controller4.tabBarItem.title = @"我的"; // 将四个页面的 UIViewController 加入到 UITabBarController 之中 [tabbarController setViewControllers: @[controller1, controller2, controller3, controller4]]; self.window.rootViewController = tabbarController; [self.window makeKeyAndVisible]; }

iOS13里生命周期有所调整需要将代码移动到SceneDelegate.m中 ``` self.window = [[UIWindow alloc] initWithWindowScene:(UIWindowScene *)scene]; UITabBarController *tabbarController = [[UITabBarController alloc] init]; UIViewController *controller1 = [[UIViewController alloc] init]; controller1.view.backgroundColor = [UIColor redColor]; controller1.tabBarItem.title = @"xinwen"; UIViewController *controller2 = [[UIViewController alloc] init]; controller2.view.backgroundColor = [UIColor greenColor]; controller2.tabBarItem.title = @"keji"; UIViewController *controller3 = [[UIViewController alloc] init]; controller3.view.backgroundColor = [UIColor blueColor]; controller3.tabBarItem.title = @"tuijian"; UIViewController *controller4 = [[UIViewController alloc] init]; controller4.view.backgroundColor = [UIColor yellowColor]; controller4.tabBarItem.title = @"wode"; [tabbarController setViewControllers:@[controller1, controller2, controller3, controller4]]; self.window.rootViewController = tabbarController; [self.window makeKeyAndVisible]; ```

7分20秒的跳转到UITabBarController，快捷操作是什么？一脸懵逼呀。

老师 ，那么改完代码自动运行是怎么设置的啊？ 不用在每次点击运行按钮了？

您好: 按照视频 7 分 16 秒时的代码设置window ： ``` - (BOOL)application:(UIApplication *)application willFinishLaunchingWithOptions:(NSDictionary<UIApplicationLaunchOptionsKey, id> *)launchOptions { self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]]; self.window.rootViewController = [[UIViewController alloc] init]; [self.window setBackgroundColor:[UIColor redColor]]; [self.window makeKeyAndVisible]; return YES; } ``` 运行程序出现以下错误： SimpleApp[37324:5421992] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[AppDelegate setWindow:]: unrecognized selector sent to instance 0x600003c580b0' 请教是什么含义呢？该怎么解决？🤝

tabbarItem这个属性是UITabBarController的属性，UIViewControlle是UITabBarController的父类，在调用时并不存在这个属性，为何不报错呢

controller3.tabBarItem.title 为什么每个UIViewController有 tabBarItem 这个属性，api的源文件里面并没有这个属性

setViewControllers:@[] @[]是加入对象的意思 ， 但是[CON1...CON4]这里面全放进去，是以数组的形式还是转换成对象的之后，返回的是数组还是什么呢？

Xcode 对代码格式化的 快捷键是什么呢？

老师如何快速补全代码，和查找系统API函数