Xcode11创建新工程

①删除Info.plist中的Application Scene Manifest这一列

②删除或注释下面的代理方法

- (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 *)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.
}

③
AppDelegate.h 中增加属性@property(nonatomic,strong)UIWindow*window;
④AppDelegate.m更改切换root

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    self.window = [[UIWindow alloc] initWithFrame:UIScreen.mainScreen.bounds];
    self.window.backgroundColor = UIColor.whiteColor;
    
    self.window.rootViewController = [OneViewController new];
    
    [self.window makeKeyAndVisible];

    return YES;
}

⑤需要注意的是后续的Controller继承对象一定要是UIViewController而不是ViewController