UINavigationController, and TabBarController programmatically (no storyboards)

Question

Currently, my AppDelegate file contains this code to establish the CustomTabBarController as the rootViewController:

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

I want my app to always have the CustomTabBarController on the bottom, but I want each tab to have a navigation controller. Here is the code I used to set up my tabBarController:

class CustomTabBarController: UITabBarController {
override func viewDidLoad() {
super.viewDidLoad()
let vc1 = FirstViewController()
let vc2 = SecondViewController()
let vc3 = ThirdViewController()
viewControllers = [vc1, vc2, vc3]
}

Here is the code I used to set up my FirstViewController:

class ProfileViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout {

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return 2
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: VCCellId, for: indexPath) as! firstVCCell

    return cell
}
}

Answer 1

When combining a UITabBarController and UINavigationControllers, the correct way to set that up is to make the UITabBarController the rootViewController. Each tab of your UITabBarController gets its own UINavigationController. So, if you have 4 tabs, you will create 4 UINavigationControllers.

See: Adding a Navigation Controller to a Tab Bar Interface

---

Update

Building off of the code you added in your updated question, create a UINavigationController for each of your vc1, vc2, and vc3.

class CustomTabBarController: UITabBarController {
    override func viewDidLoad() {
        super.viewDidLoad()
        let vc1 = UINavigationController(rootViewController: FirstViewController())
        let vc2 = UINavigationController(rootViewController: SecondViewController())
        let vc3 = UINavigationController(rootViewController: ThirdViewController())

        viewControllers = [vc1, vc2, vc3]
    }

}

In each of your ViewControllers, set title to the title you want to be displayed in the navigation bar when that tab is selected:

class FirstViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .red
        title = "First"
        self.navigationController?.navigationBar.titleTextAttributes =
            [NSFontAttributeName: UIFont(name: "Chalkduster", size: 27)!,
             NSForegroundColorAttributeName: UIColor.black]
    }
}