删除SceneDelegate

1.首先选中SceneDelegate.h和SceneDelegate.m类，右击选择Delete，选择"Move to Trash"；

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2.打开Info.plist文件，点击"Application Scene Mainfest"的➖号按钮删除该项；

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3.点击打开TARGETS->General，清空”App Icons and Lanuch Images“下的”Launch Screen File“选项。

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4.打开AppDelegate.h文件，声明UIWindow对象

@interface AppDelegate : UIResponder <UIApplicationDelegate>
@property (strong, nonatomic) UIWindow *window;
@end

5.打开AppDelegate.m文件，删除以下SceneDelegate的两个代理方法

- (UISceneConfiguration *)application:(UIApplication *)application configurationForConnectingSceneSession:(UISceneSession *)connectingSceneSession options:(UISceneConnectionOptions *)options
 {
    return [[UISceneConfiguration alloc] initWithName:@"Default Configuration" sessionRole:connectingSceneSession.role];
}
- (void)application:(UIApplication *)application didDiscardSceneSessions:(NSSet<UISceneSession *> *)sceneSessions
{
}

然后在didFinishLaunchingWithOptions方法里设置rootViewController即可。

self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
self.window.backgroundColor = UIColor.redColor;
UIViewController *vc = [[UIViewController alloc] init];
self.window.rootViewController = vc;
[self.window makeKeyAndVisible];