Our project using UITabBarController and set a custom tabbar using below code: let customTabBar = CustomTabBar(with: dataSource) setValue(customTabBar, forKey: "tabBar") But when using Xcode 26 build app in iOS 26, the tabbar does not show: above code works well in iOS 18: below is the demo code: AppDelegate.swift: import UIKit @main class AppDelegate: UIResponder, UIApplicationDelegate { let window: UIWindow = UIWindow() func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool { window.rootViewController = TabBarViewController() window.makeKeyAndVisible() return true } } CustomTabBar.swift: import UIKit class CustomTabBar: UITabBar { class TabBarModel { let title: String let icon: UIImage? init(title: String, icon: UIImage?) { self.title = title self.icon = icon } } class TabBarItemView: UIView { lazy var titleLabel: UILabel = { let titleLabel = UILabel() titleLabel.translatesAutoresizingMaskIntoConstraints = false titleLabel.font = .systemFont(ofSize: 14) titleLabel.textColor = .black titleLabel.textAlignment = .center return titleLabel }() lazy var iconView: UIImageView = { let iconView = UIImageView() iconView.translatesAutoresizingMaskIntoConstraints = false iconView.contentMode = .center return iconView }() private var model: TabBarModel init(model: TabBarModel) { self.model = model super.init(frame: .zero) setupSubViews() } required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") } private func setupSubViews() { addSubview(iconView) iconView.topAnchor.constraint(equalTo: topAnchor).isActive = true iconView.centerXAnchor.constraint(equalTo: centerXAnchor).isActive = true iconView.widthAnchor.constraint(equalToConstant: 34).isActive = true iconView.heightAnchor.constraint(equalToConstant: 34).isActive = true iconView.image = model.icon addSubview(titleLabel) titleLabel.topAnchor.constraint(equalTo: iconView.bottomAnchor).isActive = true titleLabel.leadingAnchor.constraint(equalTo: leadingAnchor).isActive = true titleLabel.trailingAnchor.constraint(equalTo: trailingAnchor).isActive = true titleLabel.heightAnchor.constraint(equalToConstant: 16).isActive = true titleLabel.text = model.title } } private var dataSource: [TabBarModel] init(with dataSource: [TabBarModel]) { self.dataSource = dataSource super.init(frame: .zero) setupTabBars() } required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") } override func sizeThatFits(_ size: CGSize) -> CGSize { var sizeThatFits = super.sizeThatFits(size) let safeAreaBottomHeight: CGFloat = safeAreaInsets.bottom sizeThatFits.height = 52 + safeAreaBottomHeight return sizeThatFits } private func setupTabBars() { backgroundColor = .orange let multiplier = 1.0 / Double(dataSource.count) var lastItemView: TabBarItemView? for model in dataSource { let tabBarItemView = TabBarItemView(model: model) addSubview(tabBarItemView) tabBarItemView.translatesAutoresizingMaskIntoConstraints = false tabBarItemView.topAnchor.constraint(equalTo: topAnchor).isActive = true tabBarItemView.bottomAnchor.constraint(equalTo: bottomAnchor).isActive = true if let lastItemView = lastItemView { tabBarItemView.leadingAnchor.constraint(equalTo: lastItemView.trailingAnchor).isActive = true } else { tabBarItemView.leadingAnchor.constraint(equalTo: leadingAnchor).isActive = true } tabBarItemView.widthAnchor.constraint(equalTo: widthAnchor, multiplier: multiplier).isActive = true lastItemView = tabBarItemView } } } TabBarViewController.swift: import UIKit class NavigationController: UINavigationController { override func viewDidLoad() { super.viewDidLoad() } } class HomeViewController: UIViewController { override func viewDidLoad() { super.viewDidLoad() view.backgroundColor = .red navigationItem.title = "Home" } } class PhoneViewController: UIViewController { override func viewDidLoad() { super.viewDidLoad() view.backgroundColor = .purple navigationItem.title = "Phone" } } class PhotoViewController: UIViewController { override func viewDidLoad() { super.viewDidLoad() view.backgroundColor = .yellow navigationItem.title = "Photo" } } class SettingViewController: UIViewController { override func viewDidLoad() { super.viewDidLoad() view.backgroundColor = .green navigationItem.title = "Setting" } } class TabBarViewController: UITabBarController { override func viewDidLoad() { super.viewDidLoad() let homeVC = HomeViewController() let homeNav = NavigationController(rootViewController: homeVC) let phoneVC = PhoneViewController() let phoneNav = NavigationController(rootViewController: phoneVC) let photoVC = PhotoViewController() let photoNav = NavigationController(rootViewController: photoVC) let settingVC = SettingViewController() let settingNav = NavigationController(rootViewController: settingVC) viewControllers = [homeNav, phoneNav, photoNav, settingNav] let dataSource = [ CustomTabBar.TabBarModel(title: "Home", icon: UIImage(systemName: "house")), CustomTabBar.TabBarModel(title: "Phone", icon: UIImage(systemName: "phone")), CustomTabBar.TabBarModel(title: "Photo", icon: UIImage(systemName: "photo")), CustomTabBar.TabBarModel(title: "Setting", icon: UIImage(systemName: "gear")) ] let customTabBar = CustomTabBar(with: dataSource) setValue(customTabBar, forKey: "tabBar") } } And I have post a feedback in Feedback Assistant(id: FB18141909), the demo project code can be found there. How are we going to solve this problem? Thank you.

When call: [UITabBarController setViewControllers:animated:] It crashed and raise an Fatal Exception: Fatal Exception: NSInternalInconsistencyException Attempting to select a view controller that isn't a child! (null) the crash stack is: Fatal Exception: NSInternalInconsistencyException 0 CoreFoundation 0x8408c __exceptionPreprocess 1 libobjc.A.dylib 0x172e4 objc_exception_throw 2 Foundation 0x82215c _userInfoForFileAndLine 3 UIKitCore 0x38a468 -[UITabBarController transitionFromViewController:toViewController:transition:shouldSetSelected:] 4 UIKitCore 0x3fa8a4 -[UITabBarController _setSelectedViewController:performUpdates:] 5 UIKitCore 0x3fa710 -[UITabBarController setSelectedIndex:] 6 UIKitCore 0x8a5fc +[UIView(Animation) performWithoutAnimation:] 7 UIKitCore 0x3e54e0 -[UITabBarController _setViewControllers:animated:] 8 UIKitCore 0x45d7a0 -[UITabBarController setViewControllers:animated:] And it appear sometimes, what's the root cause?

Our project using UISplitViewController as the root view controller for whole app. And when using the xocde26 to build app in iOS26, the layout of page is uncorrect. for iPhone, when launch app and in portrait mode, the app only show a blank page: and when rotate app to landscape, the first view controller of UISplitViewController's viewControllers will float on second view controller: and this float behavior also happens in iPad: below is the demo code: AppDelegate.swift: import UIKit @main class AppDelegate: UIResponder, UIApplicationDelegate { let window: UIWindow = UIWindow() func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool { let vc = SplitViewController(primary: TabBarViewController(), secondary: ViewController()) window.rootViewController = vc window.makeKeyAndVisible() return true } } SplitViewController: import UIKit class SplitViewController: UISplitViewController { init(primary: UIViewController, secondary: UIViewController) { super.init(nibName: nil, bundle: nil) preferredDisplayMode = .oneBesideSecondary presentsWithGesture = false delegate = self viewControllers = [primary, secondary] } required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") } override func viewDidLoad() { super.viewDidLoad() } } extension SplitViewController: UISplitViewControllerDelegate { } TabBarViewController.swift: import UIKit class FirstViewController: UIViewController { override func viewDidLoad() { super.viewDidLoad() view.backgroundColor = .red tabBarItem = UITabBarItem(title: "Home", image: UIImage(systemName: "house"), tag: 0) } } class SecondViewController: UIViewController { override func viewDidLoad() { super.viewDidLoad() view.backgroundColor = .purple tabBarItem = UITabBarItem(title: "Setting", image: UIImage(systemName: "gear"), tag: 1) } } class TabBarViewController: UITabBarController { override func viewDidLoad() { super.viewDidLoad() let firstVC = FirstViewController() let secondVC = SecondViewController() tabBar.backgroundColor = .orange viewControllers = [firstVC, secondVC] } } ViewController.swift: import UIKit class ViewController: UIViewController { override func viewDidLoad() { super.viewDidLoad() view.backgroundColor = .systemPink } } And I have post a feedback in Feedback Assistant(id: FB18004520), the demo project code can be found there.