In our app, there is a UIWindow makeKeyAndVisible crash, and for now, it appears once, crash stack:
the crash detail:
crash.txt
in the RCWindowSceneManager class's makeWindowKeyAndVisible method, we check and set a window's windowScene and makeKeyAndVisible:
public func makeWindowKeyAndVisible(_ window: UIWindow?) {
guard let window else {
return
}
if let currentWindowScene {
if window.windowScene == nil || window.windowScene != currentWindowScene {
window.windowScene = currentWindowScene
}
window.makeKeyAndVisible()
}
}
and I set a break point at a normal no crash flow, the stack is:
why it crash? and how we avoid this, thank you.
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crash stack:
Crashed: com.apple.main-thread
0 libsystem_pthread.dylib 0x90c thread_chkstk_darwin + 60
1 libsystem_pthread.dylib 0x90c ___chkstk_darwin + 60
2 CoreAutoLayout 0x14c4 -[NSISEngine _flushPendingRemovals] + 56
3 CoreAutoLayout 0x2de08 -[NSISEngine _coreReplaceMarker:withMarkerPlusDelta:].cold.1 + 64
4 CoreAutoLayout 0x15d78 -[NSISEngine _coreReplaceMarker:withMarkerPlusDelta:] + 204
5 CoreAutoLayout 0x2ce38 -[NSISEngine constraintDidChangeSuchThatMarker:shouldBeReplacedByMarkerPlusDelta:] + 108
6 CoreAutoLayout 0x15f1c -[NSISEngine tryToChangeConstraintSuchThatMarker:isReplacedByMarkerPlusDelta:undoHandler:] + 100
7 CoreAutoLayout 0x2fdbc -[NSLayoutConstraint _tryToChangeContainerGeometryWithUndoHandler:] + 252
8 CoreAutoLayout 0x3020c -[NSLayoutConstraint _setSymbolicConstant:constant:symbolicConstantMultiplier:] + 452
9 CoreAutoLayout 0x30378 -[NSLayoutConstraint setConstant:] + 84
10 UIKitCore 0x51c3c __74-[UIView(UIConstraintBasedLayout) _autoresizingConstraints_frameDidChange]_block_invoke + 140
11 UIKitCore 0x1841174 -[UIView(AdditionalLayoutSupport) _withUnsatisfiableConstraintsLoggingSuspendedIfEngineDelegateExists:] + 112
12 UIKitCore 0x51b28 -[UIView(UIConstraintBasedLayout) _autoresizingConstraints_frameDidChange] + 452
13 UIKitCore 0x2c894 -[UIView _constraints_frameDidChange] + 100
14 UIKitCore 0x18fac08 -[UIView(Geometry) setFrame:] + 576
15 UIKitCore 0x96712c -[UITabBar setFrame:] + 128
16 UIKitCore 0x1666f4 -[_UITabBarControllerVisualStyle updateTabBarLayout] + 360
17 UIKitCore 0x16671c -[_UITabBarControllerVisualStyle updateTabBarLayout] + 400
18 UIKitCore 0x16671c -[_UITabBarControllerVisualStyle updateTabBarLayout] + 400
19 UIKitCore 0x16671c -[_UITabBarControllerVisualStyle updateTabBarLayout] + 400
20 UIKitCore 0x16671c -[_UITabBarControllerVisualStyle updateTabBarLayout] + 400
21 UIKitCore 0x16671c -[_UITabBarControllerVisualStyle updateTabBarLayout] + 400
22 UIKitCore 0x16671c -[_UITabBarControllerVisualStyle updateTabBarLayout] + 400
23 UIKitCore 0x16671c -[_UITabBarControllerVisualStyle updateTabBarLayout] + 400
24 UIKitCore 0x16671c -[_UITabBarControllerVisualStyle updateTabBarLayout] + 400
25 UIKitCore 0x16671c -[_UITabBarControllerVisualStyle updateTabBarLayout] + 400
26 UIKitCore 0x16671c -[_UITabBarControllerVisualStyle updateTabBarLayout] + 400
27 UIKitCore 0x16642c -[UITabBarController _prepareTabBar] + 128
28 UIKitCore 0x166a10 -[UITabBarController _layoutContainerView] + 376
29 UIKitCore 0x1677a8 -[UITabBarController __viewWillLayoutSubviews] + 28
30 UIKitCore 0x147078 -[UILayoutContainerView layoutSubviews] + 176
31 UIKit 0xb14a0 -[UILayoutContainerViewAccessibility layoutSubviews] + 60
for a more detail crash stack, can see attach file:
crash.txt
crash probabilistic happed after app enter background, and our app support landscape, when crash appear, the system method:
/*
This method is called when the view controller's view's size is changed by its parent (i.e. for the root view controller when its window rotates or is resized).
If you override this method, you should either call super to propagate the change to children or manually forward the change to children.
*/
- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id <UIViewControllerTransitionCoordinator>)coordinator API_AVAILABLE(ios(8.0));
is called;
but for a normal not crash case, when enter background and rotate device, the viewWillTransitionToSize method is not called until app enter foreground;
Are there any suggestions that can help solve this problem, thank you.
Our project include UIKIt and SwiftUI, and in some case, we need to traverse all subviews, for UIKit implement views, below code:
func findView(byIdentifier identifier: String) -> UIView? {
if self.accessibilityIdentifier == identifier {
return self
}
for subview in subviews {
if let found = subview.findView(byIdentifier: identifier) {
return found
}
}
return nil
}
works well, but for SwiftUI implement views, like below code:
struct ContentView: View {
var body: some View {
VStack {
Image(systemName: "globe")
.imageScale(.large)
.foregroundStyle(.tint)
.accessibilityIdentifier("Image")
Text("Hello, world!")
.accessibilityIdentifier("Text")
}
.padding()
}
}
it can not find subviews in the ContentView, and only a view with type:
_UIHostingView<ModifiedContent<AnyView, RootModifier>>
can be found, the Image and Text is not found;
And because we have set a accessibilityIdentifier property, so we also try use:
@MainActor
var accessibilityElements: [Any]? { get set }
to find sub node, but this accessibilityElements is not stable, we can find the Image and Text node in iOS26.1 system:
[AX] level=3 AccessibilityNode @ 0x000000010280fb10 id=Image
[AX] level=3 AccessibilityNode @ 0x000000010161fbf0 id=Text
but can not find it in iOS26.0 and below system.
Any suggestion in how to find SwiftUI subviews? thank you
Topic:
UI Frameworks
SubTopic:
SwiftUI
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.