Amzd/UIKitTabView.swift

## UIKitTabView.swift
/// An iOS style TabView that doesn't reset it's childrens navigation stacks when tabs are switched.
public struct UIKitTabView: View {
    private var viewControllers: [UIHostingController<AnyView>]
    private var selectedIndex: Binding<Int>?
    @State private var fallbackSelectedIndex: Int = 0

    public init(selectedIndex: Binding<Int>? = nil, @TabBuilder _ views: () -> [Tab]) {
        self.viewControllers = views().map {
            let host = UIHostingController(rootView: $0.view)
            host.tabBarItem = $0.barItem
            return host
        }
        self.selectedIndex = selectedIndex
    }

    public var body: some View {
        TabBarController(controllers: viewControllers, selectedIndex: selectedIndex ?? $fallbackSelectedIndex)
            .edgesIgnoringSafeArea(.all)
    }

    public struct Tab {
        var view: AnyView
        var barItem: UITabBarItem
    }
}

@_functionBuilder
public struct TabBuilder {
    public static func buildBlock(_ items: UIKitTabView.Tab...) -> [UIKitTabView.Tab] {
        items
    }
}

extension View {
    public func tab(title: String, image: String? = nil, selectedImage: String? = nil, badgeValue: String? = nil) -> UIKitTabView.Tab {
        func imageOrSystemImage(named: String?) -> UIImage? {
            guard let name = named else { return nil }
            return UIImage(named: name) ?? UIImage(systemName: name)
        }

        let image = imageOrSystemImage(named: image)
        let selectedImage = imageOrSystemImage(named: selectedImage)
        let barItem = UITabBarItem(title: title, image: image, selectedImage: selectedImage)

        barItem.badgeValue = badgeValue

        return UIKitTabView.Tab(view: AnyView(self), barItem: barItem)
    }
}

fileprivate struct TabBarController: UIViewControllerRepresentable {
    var controllers: [UIViewController]
    @Binding var selectedIndex: Int

    func makeUIViewController(context: Context) -> UITabBarController {
        let tabBarController = UITabBarController()
        tabBarController.viewControllers = controllers
        tabBarController.delegate = context.coordinator
        tabBarController.selectedIndex = 0
        return tabBarController
    }

    func updateUIViewController(_ tabBarController: UITabBarController, context: Context) {
        tabBarController.selectedIndex = selectedIndex
    }

    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }

    class Coordinator: NSObject, UITabBarControllerDelegate {
        var parent: TabBarController

        init(_ tabBarController: TabBarController) {
            self.parent = tabBarController
        }

        func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
            if parent.selectedIndex == tabBarController.selectedIndex {
                popToRootOrScrollUp(on: viewController)
            }

            parent.selectedIndex = tabBarController.selectedIndex
        }

        private func popToRootOrScrollUp(on viewController: UIViewController) {
            let nvc = navigationController(for: viewController)
            let popped = nvc?.popToRootViewController(animated: true)

            if (popped ?? []).isEmpty {
                let rootViewController = nvc?.viewControllers.first ?? viewController
                if let scrollView = firstScrollView(in: rootViewController.view ?? UIView()) {
                    let preservedX = scrollView.contentOffset.x
                    let y = -scrollView.adjustedContentInset.top
                    scrollView.setContentOffset(CGPoint(x: preservedX, y: y), animated: true)
                }
            }
        }

        private func navigationController(for viewController: UIViewController) -> UINavigationController? {
            for child in viewController.children {
                if let nvc = viewController as? UINavigationController {
                    return nvc
                } else if let nvc = navigationController(for: child) {
                    return nvc
                }
            }
            return nil
        }

        public func firstScrollView(in view: UIView) -> UIScrollView? {
            for subview in view.subviews {
                if let scrollView = view as? UIScrollView {
                    return scrollView
                } else if let scrollView = firstScrollView(in: subview) {
                    return scrollView
                }
            }

            return nil
        }
    }
}

## zExample.swift
struct ExampleView: View {
    @State var text: String = ""

    var body: some View {
        UIKitTabView {
            NavView().tab(title: "First", badgeValue: "3")
            Text("Second View").tab(title: "Second")
        }
    }
}

struct NavView: View {
    var body: some View {
        NavigationView {
            VStack {
                NavigationLink(destination: Text("This page stays when you switch back and forth between tabs (as expected on iOS)")) {
                    Text("Go to detail")
                }
            }
        }
    }
}
	/// An iOS style TabView that doesn't reset it's childrens navigation stacks when tabs are switched.
	public struct UIKitTabView: View {
	private var viewControllers: [UIHostingController<AnyView>]
	private var selectedIndex: Binding<Int>?
	@State private var fallbackSelectedIndex: Int = 0

	public init(selectedIndex: Binding<Int>? = nil, @TabBuilder _ views: () -> [Tab]) {
	self.viewControllers = views().map {
	let host = UIHostingController(rootView: $0.view)
	host.tabBarItem = $0.barItem
	return host
	}
	self.selectedIndex = selectedIndex
	}

	public var body: some View {
	TabBarController(controllers: viewControllers, selectedIndex: selectedIndex ?? $fallbackSelectedIndex)
	.edgesIgnoringSafeArea(.all)
	}

	public struct Tab {
	var view: AnyView
	var barItem: UITabBarItem
	}
	}

	@_functionBuilder
	public struct TabBuilder {
	public static func buildBlock(_ items: UIKitTabView.Tab...) -> [UIKitTabView.Tab] {
	items
	}
	}

	extension View {
	public func tab(title: String, image: String? = nil, selectedImage: String? = nil, badgeValue: String? = nil) -> UIKitTabView.Tab {
	func imageOrSystemImage(named: String?) -> UIImage? {
	guard let name = named else { return nil }
	return UIImage(named: name) ?? UIImage(systemName: name)
	}

	let image = imageOrSystemImage(named: image)
	let selectedImage = imageOrSystemImage(named: selectedImage)
	let barItem = UITabBarItem(title: title, image: image, selectedImage: selectedImage)

	barItem.badgeValue = badgeValue

	return UIKitTabView.Tab(view: AnyView(self), barItem: barItem)
	}
	}

	fileprivate struct TabBarController: UIViewControllerRepresentable {
	var controllers: [UIViewController]
	@Binding var selectedIndex: Int

	func makeUIViewController(context: Context) -> UITabBarController {
	let tabBarController = UITabBarController()
	tabBarController.viewControllers = controllers
	tabBarController.delegate = context.coordinator
	tabBarController.selectedIndex = 0
	return tabBarController
	}

	func updateUIViewController(_ tabBarController: UITabBarController, context: Context) {
	tabBarController.selectedIndex = selectedIndex
	}

	func makeCoordinator() -> Coordinator {
	Coordinator(self)
	}

	class Coordinator: NSObject, UITabBarControllerDelegate {
	var parent: TabBarController

	init(_ tabBarController: TabBarController) {
	self.parent = tabBarController
	}

	func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
	if parent.selectedIndex == tabBarController.selectedIndex {
	popToRootOrScrollUp(on: viewController)
	}

	parent.selectedIndex = tabBarController.selectedIndex
	}

	private func popToRootOrScrollUp(on viewController: UIViewController) {
	let nvc = navigationController(for: viewController)
	let popped = nvc?.popToRootViewController(animated: true)

	if (popped ?? []).isEmpty {
	let rootViewController = nvc?.viewControllers.first ?? viewController
	if let scrollView = firstScrollView(in: rootViewController.view ?? UIView()) {
	let preservedX = scrollView.contentOffset.x
	let y = -scrollView.adjustedContentInset.top
	scrollView.setContentOffset(CGPoint(x: preservedX, y: y), animated: true)
	}
	}
	}

	private func navigationController(for viewController: UIViewController) -> UINavigationController? {
	for child in viewController.children {
	if let nvc = viewController as? UINavigationController {
	return nvc
	} else if let nvc = navigationController(for: child) {
	return nvc
	}
	}
	return nil
	}

	public func firstScrollView(in view: UIView) -> UIScrollView? {
	for subview in view.subviews {
	if let scrollView = view as? UIScrollView {
	return scrollView
	} else if let scrollView = firstScrollView(in: subview) {
	return scrollView
	}
	}

	return nil
	}
	}
	}
	struct ExampleView: View {
	@State var text: String = ""

	var body: some View {
	UIKitTabView {
	NavView().tab(title: "First", badgeValue: "3")
	Text("Second View").tab(title: "Second")
	}
	}
	}

	struct NavView: View {
	var body: some View {
	NavigationView {
	VStack {
	NavigationLink(destination: Text("This page stays when you switch back and forth between tabs (as expected on iOS)")) {
	Text("Go to detail")
	}
	}
	}
	}
	}