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

Appdelegate不在负责UI生命周期，所有UI生命周期交给SceneDelegate处理：

因此初始化window方法需要改变：
现在不再Appdelegate的- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions进行初始化，转交给SceneDelegate的willConnectToSession:方法进行根控制器设置

- (void)scene:(UIScene *)scene willConnectToSession:(UISceneSession *)session options:(UISceneConnectionOptions *)connectionOptions {
    UIWindowScene *windowScene = (UIWindowScene *)scene;
    self.window = [[UIWindow alloc] initWithWindowScene:windowScene];
    self.window.frame = windowScene.coordinateSpace.bounds;
    self.window.rootViewController = [UITabBarController new];
    [self.window makeKeyAndVisible];
}

想继续全部使用AppDelegate也是可以的，删除SceneDelegate

1，直接删除SceneDelegate.h、SceneDelegate.m文件

2，info.plist文件中删除Application Scene Manifest

8FD21B88-3FEC-47BA-9B84-AD396C7390D8.png

3，删除SceneDelegate在AppDelegate中的代理

#pragma mark - UISceneSession lifecycle
- (UISceneConfiguration *)application:(UIApplication *)application configurationForConnectingSceneSession:(UISceneSession *)connectingSceneSession options:(UISceneConnectionOptions *)options {
    // Called when a new scene session is being created.
    // Use this method to select a configuration to create the new scene with.
    return [[UISceneConfiguration alloc] initWithName:@"Default Configuration" sessionRole:connectingSceneSession.role];
}


- (void)application:(UIApplication *)application didDiscardSceneSessions:(NSSet<UISceneSession *> *)sceneSessions {
    // Called when the user discards a scene session.
    // If any sessions were discarded while the application was not running, this will be called shortly after application:didFinishLaunchingWithOptions.
    // Use this method to release any resources that were specific to the discarded scenes, as they will not return.
}

4，在AppDelegate.h添加@property (strong, nonatomic) UIWindow * window;

5，没了。