如何在SWIFT中以编程方式将我的自定义控制器转换为根控制器？(无法加载NIB)

import UIKit

class CustomViewController: UIViewController {
    // 控制器的其他代码
}

// 在AppDelegate中设置根控制器
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    let customViewController = CustomViewController(nibName: "CustomViewController", bundle: nil)
    
    if customViewController.view == nil {
        // 如果NIB加载失败，可以尝试重新加载或使用纯代码创建界面
        customViewController.loadViewIfNeeded()
    }
    
    let navigationController = UINavigationController(rootViewController: customViewController)
    window?.rootViewController = navigationController
    window?.makeKeyAndVisible()
    
    return true
}

class CustomViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        // 使用代码创建UI元素
        let label = UILabel()
        label.text = "Hello, World!"
        label.frame = CGRect(x: 0, y: 0, width: 200, height: 50)
        label.center = view.center
        view.addSubview(label)
    }
}