iOS 15+ unresponsive bug

iOSUnresponsive.swift

//
//  Created by ktiays on 2023/8/15.
//  Copyright (c) 2023 ktiays. All rights reserved.
//

/**
 * The purpose of this example is to demonstrate a bug in iOS 15 and higher versions.
 * This bug will cause the app to be completely unresponsive to any actions.
 *
 * When you open a `UISheetPresentationController` and there is a `UINavigationController` at the bottom,
 * if you swipe down to close the sheet and try to swipe sideways to return to the first level **IMMEDIATELY**.
 *
 *           ╭─────────────╮
 *           │ <Back       │
 *           │             │
 *           │             │
 *           ├─────────────┤
 *           │      ▔      │    1. Slide down to dismiss UISheetPresentationController.
 *           │             │    2. Attempt to return to the first-level page by sliding sideways.
 *           │             │
 *           │             │
 *           ╰─────────────╯
 *
 * The bug is likely caused by UIViewController triggering a second animation while the previous one has not yet finished,
 * and UIKit does not handle this situation properly.
 */

import UIKit

class SceneDelegate: UIResponder, UIWindowSceneDelegate {

    var window: UIWindow?

    func scene(
        _ scene: UIScene, willConnectTo session: UISceneSession,
        options connectionOptions: UIScene.ConnectionOptions
    ) {
        guard let windowScene = (scene as? UIWindowScene) else { return }
        window = .init(windowScene: windowScene)
        let navigationController = UINavigationController(rootViewController: RootViewController())
        navigationController.view.backgroundColor = .systemBackground
        window?.rootViewController = navigationController
        window?.makeKeyAndVisible()
    }

}

extension UIViewController {
    func makeButtonOnCenter(title: String, action: @escaping () -> Void) {
        var configuration = UIButton.Configuration.filled()
        configuration.buttonSize = .large
        configuration.cornerStyle = .large
        configuration.title = title
        let button = UIButton(
            configuration: configuration,
            primaryAction: .init { _ in
                action()
            }
        )
        self.view.addSubview(button)
        button.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            button.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            button.centerYAnchor.constraint(equalTo: view.centerYAnchor),
        ])
    }
}

class _SystemBackgroundViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .systemBackground
    }
}

class RootViewController: _SystemBackgroundViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        title = "Root View Controller"

        makeButtonOnCenter(title: "Push") { [unowned self] in
            self.navigationController?.pushViewController(DetailViewController(), animated: true)
        }
    }
}

class DetailViewController: _SystemBackgroundViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        title = "Detail View Controller"

        makeButtonOnCenter(title: "Open Sheet") { [unowned self] in
            let viewController = _SystemBackgroundViewController()
            if let sheet = viewController.sheetPresentationController {
                sheet.detents = [.medium(), .large()]
                sheet.prefersGrabberVisible = true
            }
            self.present(viewController, animated: true)
        }
    }
}