Question about using native iOS navigation hosting...

# compose

[Stylianos Gakis]

Question about using native iOS navigation hosting individual ComposeUIViewControllers as destinations (each via UIViewControllerRepresentable, no Compose-side navigation).
The system back-swipe and Compose's input pipeline don't coordinate. When swiping from the leading edge, the back-pop animates and Compose simultaneously scrolls horizontally/vertically on whatever's underneath the finger.
Has anyone actually shipped this in a way which feels nice and native without such issues of the input propagating to both the navigation back and the compose view itself?

[Stylianos Gakis]

Tried doing smth like this, to wrap my ViewController:

struct ComposeHost: UIViewControllerRepresentable {
    func makeUIViewController(context: Context) -> UIViewController {
        let composeVC = SomeFileKt.ViewController()
        return SwipeBackHostingController(child: composeVC)
    }
    func updateUIViewController(_ uiViewController: UIViewController, context: Context) {}
}
...
fun ViewController(): UIViewController {
 return ComposeUIViewController { ... compose code }
}

[Stylianos Gakis]

Where the SwipeBackhostingController is an amalgamation that I got from AI to be honest which looks like this:

import UIKit

private let edgeSwipeZoneWidth: CGFloat = 16

private final class EdgeSwipePassthroughView: UIView {
    override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
        let isRTL = effectiveUserInterfaceLayoutDirection == .rightToLeft
        let inLeadingZone = isRTL
            ? point.x > bounds.maxX - edgeSwipeZoneWidth
            : point.x < edgeSwipeZoneWidth
        if inLeadingZone {
            return nil
        }
        return super.hitTest(point, with: event)
    }
}

final class SwipeBackHostingController: UIViewController, UIGestureRecognizerDelegate {
    private let child: UIViewController
    private weak var previousDelegate: UIGestureRecognizerDelegate?

    init(child: UIViewController) {
        self.child = child
        super.init(nibName: nil, bundle: nil)
    }

    required init?(coder: NSCoder) { fatalError("init(coder:) is not used") }

    override func loadView() {
        view = EdgeSwipePassthroughView()
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        addChild(child)
        child.view.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(child.view)
        NSLayoutConstraint.activate([
                                        child.view.topAnchor.constraint(equalTo: view.topAnchor),
                                        child.view.bottomAnchor.constraint(equalTo: view.bottomAnchor),
                                        child.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
                                        child.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
                                    ])
        child.didMove(toParent: self)
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        guard let recognizer = navigationController?.interactivePopGestureRecognizer else { return }
        previousDelegate = recognizer.delegate
        recognizer.delegate = self
        recognizer.isEnabled = true
        recognizer.addTarget(self, action: #selector(handleInteractivePop(_:)))
    }

    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        guard let recognizer = navigationController?.interactivePopGestureRecognizer else { return }
        if recognizer.delegate === self {
            recognizer.delegate = previousDelegate
        }
        recognizer.removeTarget(self, action: #selector(handleInteractivePop(_:)))
        // Always restore — if we leave the screen mid-gesture we mustn't leak a disabled child.
        child.view.isUserInteractionEnabled = true
    }

    func gestureRecognizerShouldBegin(_: UIGestureRecognizer) -> Bool {
        (navigationController?.viewControllers.count ?? 0) > 1
    }

    /// When the system's edge-pan fires, Compose may already be tracking the same touch
    /// (e.g. as a horizontal scroll on a list row). Toggling `isUserInteractionEnabled`
    /// makes UIKit deliver `touchesCancelled` so Compose abandons the in-flight gesture.
    /// Restored on gesture end so taps work again immediately.
    @objc private func handleInteractivePop(_ gesture: UIGestureRecognizer) {
        switch gesture.state {
        case .began:
            child.view.isUserInteractionEnabled = false
        case .ended, .cancelled, .failed:
            child.view.isUserInteractionEnabled = true
        default:
            break
        }
    }
}

[Stylianos Gakis]

But in general it is never perfect.

[Stylianos Gakis]

If I do nothing, then the back navigation gesture simply does not work

[Stylianos Gakis]

With this wrapper either:
• the input is propagated to both the native navigation and the compose view at the same time
• the edgeSwipeZoneWidth being big enough introduces a "dead zone" at the edge where neither of the two systems receive the input

[Stylianos Gakis]

Using latest compose fwiw, CMP 1.11.0-rc01 and Kotlin 2.3.20.