如何删除SceneDelegate+whose view is

新建了一个工程使用下面获取rootVC用来弹窗时，弹出不来，发现RootViewControlle是nil

UIViewController *RootViewController()
{
    id<UIApplicationDelegate> delegate= [UIApplication sharedApplication].delegate;
    if([delegate respondsToSelector:@selector(window)]){
        UIWindow *window = [(NSObject *)delegate valueForKey:@"window"];
        UIViewController *controller = window.rootViewController;
        while (controller.presentedViewController) {
            controller = controller.presentedViewController;
        }
        return controller;
    }
    return nil;
}

需要删除 SceneDelegate 使用 AppDelegate

Xcode11之后新创建的工程会多出两个文件SceneDelegate。那么我们如何让它变回之前的那样的工程呢。

一、将这两个文件删除。
会报错There is no scene delegate set. A scene delegate class must be specified to use a main storyboard file.
二、将Info.plis 的 UIApplicationSceneManifest 删除
三、将AppDelegate.m中的UISceneSession lifecycle注释掉或者删掉。
四、在AppDelegate.h加入window。在didFinishLaunchingWithOptions中加入UIWindow。

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

@end



- (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 = [[ViewController alloc] init];;
    
    [self.window makeKeyAndVisible];
    return YES;
}

删除后继续报错 whose view is not in the window hierarchy .我是demo里面遇到的，在viewDidLoad弹一个alertViewController，所以移到外面就好了

1. 在 一个 ViewController 里面调用另外一个 ViewController 是出现这个错误：

该错误一般是由于在 viewDidLoad 里面调用引起的，解决办法是转移到 viewDidAppear 方法里面

2. 在 AppDelegate.m 中调用遇到这个错误

解决办法1：

UIViewController *topRootViewController = [UIApplication sharedApplication].keyWindow.rootViewController;
while (topRootViewController.presentedViewController)
{
   topRootViewController = topRootViewController.presentedViewController;
}

//[topRootViewController presentViewController:yourController animated:YES completion:nil];
//or
[topRootViewController myMethod];

解决办法2：

UIStoryboard *mainstoryboard = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];
   LoginViewController* loginViewController = [mainstoryboard instantiateViewControllerWithIdentifier:@"LoginViewController"];
   [self.window makeKeyAndVisible];
//[LoginViewController presentViewController:yourController animated:YES completion:nil];
//or
[LoginViewController myMethod];