Safe area not working in custom TabBarController's ViewController - swift

Question

In the didFinishLaunchingWithOptions of my app's AppDelegate, after initializing my UIWindow property, I set the root controller to a subclass of UITabBarController, in which I set the view controllers (and some other custom behaviour).
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
self.window = UIWindow(frame: UIScreen.main.bounds)
self.window?.rootViewController = TabBarController() // a subclass of UITabBarController
self.window?.makeKeyAndVisible()
return true
}
The issue I have is that the safe areas in the TabBarController's view controllers does not seem to work properly.
eg: sticking a view to the bottom of a view controller's view, using it's safeAreaLayoutGuide, goes behind the tab bar.
self.bottomView.bottomAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.bottomAnchor)
The custom behaviour (such as set tint colors, set the viewControllers and their tab bar items, or set the tabBarController's delegate - nothing crazy here) setup is made in it's viewDidLoad.
NB: I work in code only, I do not use interface builder.

Answer 1

The issue was the way I presented programmatically the tab bar controller.
What I did in the AppDelegate's didFinishLaunchingWithOptions was :
self.window?.rootViewController = MyTabBarController()
self.window?.makeKeyAndVisible()
I fixed the issue buy putting the tabbar in in a NavigationController :
let navigationController = UINavigationController(rootViewController: MyTabBarController())
self.window?.rootViewController = navigationController
self.window?.makeKeyAndVisible()

Answer 2

Can't reproduce. Here's the complete code for a view controller in a project that does what you seem to describe:
class FirstViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let v = UIView()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = .red
self.view.addSubview(v)
v.widthAnchor.constraint(equalToConstant: 100).isActive = true
v.heightAnchor.constraint(equalToConstant: 100).isActive = true
v.centerXAnchor.constraint(equalTo: self.view.centerXAnchor).isActive = true
v.bottomAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.bottomAnchor).isActive = true
}
}
And here's the result; the red square appears exactly where we expect to see it, pinned to the top of the tab bar: