Programmatically create a UINavigationController and UITabBarController

AppDelegate.swift

import UIKit

@main
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        self.window = UIWindow(frame: UIScreen.main.bounds)

        let vc = ViewController()
        vc.tabBarItem.title = "Tab 1"
        let vc2 = ViewController()
        vc2.tabBarItem.title = "Tab 2"
        let vc3 = ViewController()
        vc3.tabBarItem.title = "Tab 3"

        let add = UIBarButtonItem(barButtonSystemItem: .add, target: self, action: nil)
        let add2 = UIBarButtonItem(barButtonSystemItem: .add, target: self, action: nil)
        let add3 = UIBarButtonItem(barButtonSystemItem: .add, target: self, action: nil)
        vc.navigationItem.leftBarButtonItems = [add, add2, add3]

        let viewControllers = [vc, vc2, vc3].map { UINavigationController(rootViewController: $0)}
        viewControllers.forEach { $0.title = $0.viewControllers[0].tabBarItem.title }

        let tabBarController = UITabBarController()
        tabBarController.viewControllers = viewControllers

        self.window?.rootViewController = tabBarController
        self.window?.makeKeyAndVisible()

        return true
    }
}