Control Interactive Dismissal of Navigation Zoom Transition SwiftUI

NavigationAllowedDismissalGesturesModifier.swift

import SwiftUI
import UIKit
import Foundation

// MARK: - AllowedNavigationDismissalGestures

public struct AllowedNavigationDismissalGestures: OptionSet, Sendable {
    public let rawValue: Int
    
    public init(rawValue: Int) {
        self.rawValue = rawValue
    }
    
    public static let none: AllowedNavigationDismissalGestures = []
    
    /// Default behaviour
    public static let all: AllowedNavigationDismissalGestures = [.swipeToGoBack, .zoomTransitionGesturesOnly]
    
    /// Includes both regular left-right swipe to go back and edge-pan for zoom transition dismisall
    public static let edgePanGesturesOnly: AllowedNavigationDismissalGestures = [.swipeToGoBack, .zoomEdgePanToDismiss]
    
    /// Includes all zoom transition gestures: edge-pan, swipe-down, pinch
    public static let zoomTransitionGesturesOnly: AllowedNavigationDismissalGestures = [.zoomEdgePanToDismiss, .zoomSwipeDownToDismiss, .zoomPinchToDismiss]
    
    public static let swipeToGoBack = AllowedNavigationDismissalGestures(rawValue: 1 << 0)
    public static let zoomEdgePanToDismiss = AllowedNavigationDismissalGestures(rawValue: 1 << 1)
    public static let zoomSwipeDownToDismiss = AllowedNavigationDismissalGestures(rawValue: 1 << 2)
    public static let zoomPinchToDismiss = AllowedNavigationDismissalGestures(rawValue: 1 << 3)
}

public extension View {
    func navigationAllowDismissalGestures(_ gestures: AllowedNavigationDismissalGestures = .all) -> some View {
        modifier(NavigationAllowedDismissalGesturesModifier(allowedDismissalGestures: gestures))
    }
}

// MARK: - NavigationAllowedDismissalGesturesModifier

private struct NavigationAllowedDismissalGesturesModifier: ViewModifier {
    var allowedDismissalGestures: AllowedNavigationDismissalGestures
    
    func body(content: Content) -> some View {
        content
            .background(
                NavigationDismissalGestureUpdater(allowedDismissalGestures: allowedDismissalGestures)
                    .frame(width: .zero, height: .zero)
            )
    }
}

// MARK: - NavigationDismissalGestureUpdater

private struct NavigationDismissalGestureUpdater: UIViewControllerRepresentable {
    @State private var viewMountRetryCount = 0
    
    var allowedDismissalGestures: AllowedNavigationDismissalGestures
    
    func makeUIViewController(context: Context) -> UIViewController { .init() }
    
    func updateUIViewController(_ viewController: UIViewController, context: Context) {
        Task { @MainActor in
            guard
                let parentVC = viewController.parent,
                let navigationController = parentVC.navigationController
            else {
                // updateUIViewController could get called a bit too early
                // before the view heirarchy has been fully setup
                if viewMountRetryCount < Constants.maxRetryCountForNavigationHeirarchy {
                    viewMountRetryCount += 1
                    try await Task.sleep(for: .milliseconds(100))
                    return updateUIViewController(viewController, context: context)
                } else {
                    // unable to find navigation controller
                    return
                }
            }
            
            guard navigationController.topViewController == parentVC else {
                return
            }
            
            navigationController.interactivePopGestureRecognizer?.isEnabled = allowedDismissalGestures.contains(.swipeToGoBack)
            
            let viewLevelGestures = parentVC.view.gestureRecognizers ?? []
            for gesture in viewLevelGestures {
                switch String(describing: type(of: gesture)) {
                case Constants.zoomEdgePanToDismissClassType:
                    gesture.isEnabled = allowedDismissalGestures.contains(.zoomEdgePanToDismiss)
                    
                case Constants.zoomSwipeDownToDismissClassType:
                    gesture.isEnabled = allowedDismissalGestures.contains(.zoomSwipeDownToDismiss)
                    
                case Constants.zoomPinchToDismissClassType:
                    gesture.isEnabled = allowedDismissalGestures.contains(.zoomPinchToDismiss)
                    
                default:
                    continue
                }
            }
        }
    }
    
    static func dismantleUIViewController(_ viewController: UIViewController, coordinator: Coordinator) {
        viewController.parent?.navigationController?.interactivePopGestureRecognizer?.isEnabled = true
        (viewController.parent?.view.gestureRecognizers ?? []).forEach({ gesture in
            if Constants.navigationZoomGestureTypeClasses.contains(String(describing: type(of: gesture))) {
                gesture.isEnabled = true
            }
        })
    }
    
    // MARK: Private
    
    private enum Constants {
        static let maxRetryCountForNavigationHeirarchy = 2
        
        // These are private Navigation related UIKit gesture recognizers that we want to disable
        // when the swipe to go back is disabled.
        static let zoomEdgePanToDismissClassType: String = "_UIParallaxTransitionPanGestureRecognizer" // Edge pan zoom transition dismissal gesture
        static let zoomSwipeDownToDismissClassType: String = {
            // Swipe down to dismiss gesture
            if #available(iOS 26, *) {
                "_UIContentSwipeDismissGestureRecognizer"
            } else {
                "_UISwipeDownGestureRecognizer"
            }
        }()
        static let zoomPinchToDismissClassType: String = "_UITransformGestureRecognizer" // Pinch to dismiss gesture
        
        static let navigationZoomGestureTypeClasses: Set<String> = [
            zoomEdgePanToDismissClassType,
            zoomSwipeDownToDismissClassType,
            zoomPinchToDismissClassType,
        ]
    }
}

@vincefried @DabbyNdubisi thanks for your replies!

This solution saved me — it allows me to keep Apple’s native smooth animations while preserving our app’s design.

However, it breaks in the following scenario:
If the design does not allow pinch-to-dismiss but allows swipe-to-dismiss, when the user swipes down slightly and releases (staying on the current page), they can then use pinch to dismiss the page.

If anyone encounters the same issue, instead of disabling the gesture, remove the gesture recognizer directly from the parent view.

Like this:

if !allowedDismissalGestures.contains(/* Your allowed gesture */) {
    parentVC.view?.removeGestureRecognizer(gesture)
}

Hope this helps anyone facing the same issue.