1class ViewController: UIViewController {
2    override func viewDidLoad() {
3        super.viewDidLoad()
4
5        // This may trigger the warning if called before
6        // the view controller is fully in the hierarchy
7        let alert = UIAlertController(title: "Hello", message: "World", preferredStyle: .alert)
8        alert.addAction(UIAlertAction(title: "OK", style: .default))
9        present(alert, animated: true)  // Warning if self is detached
10    }
11}

1class ViewController: UIViewController {
2    override func viewDidAppear(_ animated: Bool) {
3        super.viewDidAppear(animated)
4
5        // Safe — the view controller is fully in the hierarchy
6        let alert = UIAlertController(title: "Welcome", message: "You are logged in", preferredStyle: .alert)
7        alert.addAction(UIAlertAction(title: "OK", style: .default))
8        present(alert, animated: true)
9    }
10}

1extension UIViewController {
2    static var topMost: UIViewController? {
3        var topController = UIApplication.shared.connectedScenes
4            .compactMap { ($0 as? UIWindowScene)?.keyWindow?.rootViewController }
5            .first
6
7        while let presented = topController?.presentedViewController {
8            topController = presented
9        }
10
11        // Handle navigation and tab controllers
12        if let nav = topController as? UINavigationController {
13            topController = nav.visibleViewController
14        }
15        if let tab = topController as? UITabBarController {
16            topController = tab.selectedViewController
17        }
18
19        return topController
20    }
21}
22
23// Usage from anywhere
24UIViewController.topMost?.present(alertController, animated: true)

1// Simple approach — present from the window's root
2func presentFromRoot(_ viewController: UIViewController, animated: Bool = true) {
3    guard let windowScene = UIApplication.shared.connectedScenes.first as? UIWindowScene,
4          let rootVC = windowScene.windows.first?.rootViewController else {
5        return
6    }
7
8    // Dismiss any existing presentation first
9    if rootVC.presentedViewController != nil {
10        rootVC.dismiss(animated: false) {
11            rootVC.present(viewController, animated: animated)
12        }
13    } else {
14        rootVC.present(viewController, animated: animated)
15    }
16}

1class ParentVC: UIViewController {
2    func showFirst() {
3        let firstVC = FirstViewController()
4        firstVC.onDismiss = { [weak self] in
5            // BAD: presenting immediately after dismiss — firstVC may still be detached
6            let secondVC = SecondViewController()
7            self?.present(secondVC, animated: true)
8        }
9        present(firstVC, animated: true)
10    }
11}
12
13class FirstViewController: UIViewController {
14    var onDismiss: (() -> Void)?
15
16    func done() {
17        dismiss(animated: true) { [weak self] in
18            // GOOD: present in the dismiss completion handler
19            self?.onDismiss?()
20        }
21    }
22}

1// BAD: child view controller presenting directly
2class ChildVC: UIViewController {
3    func showAlert() {
4        let alert = UIAlertController(title: "Error", message: "Something failed", preferredStyle: .alert)
5        alert.addAction(UIAlertAction(title: "OK", style: .default))
6        // This may warn if ChildVC is embedded but not the presenting controller
7        present(alert, animated: true)
8    }
9}
10
11// GOOD: delegate to the parent or use the top view controller
12class ChildVC: UIViewController {
13    func showAlert() {
14        let alert = UIAlertController(title: "Error", message: "Something failed", preferredStyle: .alert)
15        alert.addAction(UIAlertAction(title: "OK", style: .default))
16
17        // Present from the nearest non-detached ancestor
18        let presenter = parent ?? self
19        presenter.present(alert, animated: true)
20    }
21}

1// Check if a view controller is in the hierarchy
2func isInHierarchy(_ vc: UIViewController) -> Bool {
3    return vc.viewIfLoaded?.window != nil
4}
5
6// Log the view controller chain
7func printHierarchy() {
8    var vc = UIApplication.shared.connectedScenes
9        .compactMap { ($0 as? UIWindowScene)?.keyWindow?.rootViewController }
10        .first
11
12    var depth = 0
13    while let current = vc {
14        print("\(String(repeating: "  ", count: depth))\(type(of: current))")
15        if let nav = current as? UINavigationController {
16            print("\(String(repeating: "  ", count: depth + 1))Stack: \(nav.viewControllers.map { type(of: $0) })")
17        }
18        vc = current.presentedViewController
19        depth += 1
20    }
21}