Swift：根据配置不同的标题放置

Question

我有两种配置给我不同的结果：

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
      
        guard let windowScene = (scene as? UIWindowScene) else { return }
        let window = UIWindow(windowScene: windowScene)
        let rootVC = MainController()
        window.rootViewController = rootVC
        self.window = window
        window.makeKeyAndVisible()
    }

class MainController: UIViewController {
    
    var titleLabel = UILabel()


    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .white
        
        titleLabel.text = "Grocery List"
        titleLabel.textColor = .black
        titleLabel.font = .systemFont(ofSize: 20, weight: .bold)
        titleLabel.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(titleLabel)
    [enter image description here][1]
        setupConstraints()
    }
    
    func setupConstraints() {
        
        let padding: CGFloat = 15
        
        NSLayoutConstraint.activate([
            titleLabel.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: padding),
            titleLabel.centerXAnchor.constraint(equalTo: view.centerXAnchor)
        ])
    }
}

第一个配置

但是，如果我这样做

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        guard let _ = (scene as? UIWindowScene) else { return }
        window?.rootViewController = UINavigationController(rootViewController: MainController())
    }

这不一样。 为什么？ 我认为主要问题是我真的不知道配置细节在做什么，所以我很困惑为什么不同的设置会给我不同的结果。 谢谢！

第二个配置