iOS Application UIViewController's hierarchy monitor

AppDelegate.swift

import UIKit

@main
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
    
    private func setupWindow() {
        window = UIWindow(frame: UIScreen.main.bounds)
        window?.makeKeyAndVisible()
    }
    
    // MARK: - User Interface
    
    private func showUserInterface() {
    }
    
    // MARK: - User Interface Monitoring
    
    private var userInterfaceMonitoringTimer: Timer?
    
    private func startUserInterfaceMonitoring() {
        lastMonitoringResult = ""
        userInterfaceMonitoringTimer?.invalidate()
        userInterfaceMonitoringTimer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { (timer) in
            self.monitorUserInterface()
        }
        monitorUserInterface()
    }
    
    private func stopUserInterfaceMonitoring() {
        userInterfaceMonitoringTimer?.invalidate()
        userInterfaceMonitoringTimer = nil
    }
    
    private var lastMonitoringResult = ""
    
    private func monitorUserInterface() {
        guard let rootVC = window?.rootViewController else {
            return
        }
        
        var result = ""
        var presentedVCs = Set<UIViewController>()
        
        func build(_ vc: UIViewController, indent: String = "") {
            result += indent + "\(vc)\n"
            
            if let presentedVC = vc.presentedViewController {
                if presentedVCs.contains(presentedVC) {
                    result += indent + "  presented: \(presentedVC)\n"
                } else {
                    presentedVCs.insert(presentedVC)
                    result += indent + "  presented:\n"
                    build(presentedVC, indent: indent + "    ")
                }
            }
            
            if let presentingVC = vc.presentingViewController {
                result += indent + "  presenting: \(presentingVC)\n"
            }
            
            if vc.children.count > 0 {
                result += indent + "  children:\n"
                for child in vc.children {
                    build(child, indent: indent + "    ")
                }
            }
        }
        
        build(rootVC)
        
        if lastMonitoringResult != result {
            lastMonitoringResult = result
            print(result)
        }
    }
    
    // MARK: - UIApplicationDelegate

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        setupWindow()
        showUserInterface()
        startUserInterfaceMonitoring()
        return true
    }
}

log.txt

<RootViewController: 0x10b306c20>
  presented:
    <ProfileViewController: 0x10930a130>
      presented:
        <UINavigationController: 0x10b83c000>
          presenting: <ProfileViewController: 0x10930a130>
          children:
            <PersonalDataViewController: 0x10b308ad0>
              presenting: <ProfileViewController: 0x10930a130>
            <PersonalEmailViewController: 0x106f16df0>
              presenting: <ProfileViewController: 0x10930a130>
      presenting: <RootViewController: 0x10b306c20>
  children:
    <UINavigationController: 0x10c81ee00>
      presented: <ProfileViewController: 0x10930a130>
      children:
        <HomeViewController: 0x109216270>
          presented: <ProfileViewController: 0x10930a130>
    <MenuViewController: 0x106b2bf70>
      presented: <ProfileViewController: 0x10930a130>