如何将TabBar添加到基于NavigationController的iPhone应用程序

import UIKit

class TabBarController: UITabBarController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let firstViewController = UINavigationController(rootViewController: FirstViewController())
        firstViewController.tabBarItem = UITabBarItem(title: "First", image: UIImage(systemName: "square.grid.2x2"), tag: 0)

        let secondViewController = UINavigationController(rootViewController: SecondViewController())
        secondViewController.tabBarItem = UITabBarItem(title: "Second", image: UIImage(systemName: "list.bullet"), tag: 1)

        let tabBarList = [firstViewController, secondViewController]

        viewControllers = tabBarList
    }
}

class FirstViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }
}

class SecondViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }
}

import UIKit

@main
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.

        let tabBarController = TabBarController()

        window = UIWindow(frame: UIScreen.main.bounds)
        window?.rootViewController = tabBarController
        window?.makeKeyAndVisible()

        return true
    }
}