UITabBarController中的UINavigationController没有完全包装UIViewController

// 在UITabBarController的子类中设置标签对应的UIViewController
class MyTabBarController: UITabBarController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建并设置第一个标签对应的UIViewController
        let firstViewController = FirstViewController()
        let firstNavigationController = UINavigationController(rootViewController: firstViewController)
        firstNavigationController.tabBarItem = UITabBarItem(title: "First", image: nil, selectedImage: nil)
        
        // 创建并设置第二个标签对应的UIViewController
        let secondViewController = SecondViewController()
        let secondNavigationController = UINavigationController(rootViewController: secondViewController)
        secondNavigationController.tabBarItem = UITabBarItem(title: "Second", image: nil, selectedImage: nil)
        
        // 将创建的UIViewController添加到UITabBarController中
        viewControllers = [firstNavigationController, secondNavigationController]
    }
}

// 在每个标签对应的UIViewController中进行自定义操作
class FirstViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 在这里进行自定义操作
    }
}

class SecondViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 在这里进行自定义操作
    }
}