Deep programmatic SwiftUI NavigationView navigation

Question

I'm trying to get a deep nested programmatic navigation stack in order. The following code works as expected when navigation is done by hand (ie: pressing the links). When you press the Set Nav button the navigation stack does change - but not as expected - and you end up with a broken stack [start -> b -> bbb] with much flipping between views

class NavState: ObservableObject {
    @Published var firstLevel: String? = nil
    @Published var secondLevel: String? = nil
    @Published var thirdLevel: String? = nil
}

struct LandingPageView: View {

    @ObservedObject var navigationState: NavState

    func resetNav() {
        self.navigationState.firstLevel = "b"
        self.navigationState.secondLevel = "ba"
        self.navigationState.thirdLevel = "bbb"
    }

    var body: some View {

        return NavigationView {
            List {
                NavigationLink(
                    destination: Place(
                        text: "a",
                        childValues: [ ("aa", [ "aaa"]) ],
                        navigationState: self.navigationState
                    ).navigationBarTitle("a"),
                    tag: "a",
                    selection: self.$navigationState.firstLevel
                ) {
                    Text("a")
                }
                NavigationLink(
                    destination: Place(
                        text: "b",
                        childValues: [ ("bb", [ "bbb"]), ("ba", [ "baa", "bbb" ]) ],
                        navigationState: self.navigationState
                    ).navigationBarTitle("b"),
                    tag: "b",
                    selection: self.$navigationState.firstLevel
                ) {
                    Text("b")
                }

                Button(action: self.resetNav) {
                    Text("Set Nav")
                }
            }
            .navigationBarTitle("Start")
        }
        .navigationViewStyle(StackNavigationViewStyle())
    }
}


struct Place: View {
    var text: String
    var childValues: [ (String, [String]) ]

    @ObservedObject var navigationState: NavState

    var body: some View {
        List(childValues, id: \.self.0) { childValue in
            NavigationLink(
                destination: NextPlace(
                    text: childValue.0,
                    childValues: childValue.1,
                    navigationState: self.navigationState
                ).navigationBarTitle(childValue.0),
                tag: childValue.0,
                selection: self.$navigationState.secondLevel
            ) {
                Text(childValue.0)
            }
        }
    }
}

struct NextPlace: View {
    var text: String
    var childValues: [String]

    @ObservedObject var navigationState: NavState

    var body: some View {
        List(childValues, id: \.self) { childValue in
            NavigationLink(
                destination: FinalPlace(
                    text: childValue,
                    navigationState: self.navigationState
                ).navigationBarTitle(childValue),
                tag: childValue,
                selection: self.$navigationState.thirdLevel
            ) {
                Text(childValue)
            }
        }
    }
}

struct FinalPlace: View {
    var text: String
    @ObservedObject var navigationState: NavState

    var body: some View {
        let concat: String = "\(navigationState.firstLevel)/\(navigationState.secondLevel))/\(navigationState.thirdLevel)/"

        return VStack {
            Text(text)
            Text(concat)
        }
    }
}

I originally attempted to tackle navigation transition animations as a problem source - but How to disable NavigationView push and pop animations is suggesting that this is not configurable

Are there any sane examples of >1 level programmatic navigation working out there?

Edit: Part of what I am looking to get here is also initial state for navigation working correctly - if I come in from an external context with a navigation state I wish to reflect (ie: from a notification with some in-app context to start from, or from a saved-to-disk-encoded-state) then I would expect to be able to load up the top View with navigation correctly pointing to the right child view. Essentially - replace the nils in the NavState with real values. Qt's QML and ReactRouter can both do this declaratively - SwiftUI should be able to as well.

Answer 1

Update: Xcode 14 / SwiftUI4

Now we have NavigationStack with dynamic heterogenous path support. So updated approach could be as follows.

Note: although original could be simplified now a lot: a) I wanted preserve view hierarchy b) I wanted to show handling of different model types

Tested with Xcode 14 / iOS 16

Test on GitHub

struct LandingPageView2: View {
    class NavState: ObservableObject {
        @Published var path = NavigationPath()
        let level1 = [
            "a" : ["bb", "ba"],
            "b" : ["bb", "ba"]
        ]
        let level2 = [
            "bb" : ["baa", "bbb"],
            "ba" : ["baa", "bbb"]
        ]
    }
    struct Lev1: Hashable {
        var text: String
    }
    struct Lev2: Hashable {
        var text: String
    }
    struct Lev3: Hashable {
        var text: String
    }

    func resetNav() {
        self.navigationState.path.append(Lev1(text: "b"))
        self.navigationState.path.append(Lev2(text: "ba"))
        self.navigationState.path.append(Lev3(text: "bbb"))
    }

    @ObservedObject var navigationState: NavState

    var body: some View {
        NavigationStack(path: $navigationState.path) {
            List {
                NavigationLink("a", value: Lev1(text: "a"))
                NavigationLink("b", value: Lev1(text: "b"))
                Button(action: self.resetNav) {
                    Text("Set Nav")
                }
            }
            .navigationDestination(for: Lev1.self) {
                Place(text: $0.text, childValues: navigationState.level1[$0.text] ?? [])
            }
            .navigationDestination(for: Lev2.self) {
                NextPlace(text: $0.text, childValues: navigationState.level2[$0.text] ?? [])
            }
            .navigationDestination(for: Lev3.self) {
                FinalPlace(text: $0.text)
            }
            .navigationBarTitle("Start")
        }
        .navigationViewStyle(StackNavigationViewStyle())
        .environmentObject(navigationState)
    }
    
    // MARK: -
    struct Place: View {
        var text: String
        var childValues: [String]

        var body: some View {
            List(childValues, id: \.self) {
                NavigationLink($0, value: Lev2(text: $0))
            }
            .navigationTitle(text)
        }
    }
    struct NextPlace: View {
        var text: String
        var childValues: [String]

        var body: some View {
            List(childValues, id: \.self) {
                NavigationLink($0, value: Lev3(text: $0))
            }
            .navigationTitle(text)
        }
    }
    struct FinalPlace: View {
        var text: String
        @EnvironmentObject var navigationState: NavState

        var body: some View {
            VStack {
                Text(text)
            }
        }
    }
}

Original

This is because new stack level is formed when animation is completed, and that's why it works in the case of manual tap.

With the following modification it works:

func resetNav() {
    self.navigationState.firstLevel = "b"
    DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
        self.navigationState.secondLevel = "ba"
        DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
            self.navigationState.thirdLevel = "bbb"
        }
    }
}

Answer 2

The simplest way is to remove the @Published for the succeeding levels.

 class NavState: ObservableObject {
  @Published var firstLevel: String? = nil
    var secondLevel: String? = nil
    var thirdLevel: String? = nil
 }

This is also telling you how to conditionally change the variables may affect the navigation behaviors.

Answer 3

Putting my own solution up here as a option in the case that someone is hitting the same requirements for navigation that NavigationView does not seem to be able fulfill. In my book - functionality is a lot harder to fix than graphical elements and animation. Inspired by https://medium.com/swlh/swiftui-custom-navigation-view-for-your-applications-7f6effa7dbcf

It works off the idea of a single declarative variable at the root level determines the navigation stack - binding to individual variables seems odd when an operation like jumping from the a chain to the b chain in my above demo or starting at a particular position is required

I've used the concept of a stringified path like a URI as the variable concept - this could probably be replaced with a more expressive model (like a vector of enums)

Big ol caveats - its very rough, has no animations, doesn't look native at all, uses AnyView, you can't have the same node name more than once, only reflects a StackNavigationViewStyle, etc - if I make this into something more pretty, sane and generic I'll put that up in Gist.

struct NavigationElement {
    var tag: String
    var title: String
    var viewBuilder: () -> AnyView
}

class NavigationState: ObservableObject {
    let objectWillChange = ObservableObjectPublisher()

    var stackPath: [String] {
        willSet {
            if rectifyRootElement(path: newValue) {
                _stackPath = newValue
                rectifyStack(path: newValue, elements: _stackElements)
            }
        }
    }

    /// Temporary storage for the most current stack path during transition periods
    private var _stackPath: [String] = []

    @Published var stack: [NavigationElement] = []

    var stackElements: [String : NavigationElement] = [:] {
        willSet {
            _stackElements = newValue
            rectifyStack(path: _stackPath, elements: newValue)
        }
    }

    /// Temporary storage for the most current stack elements during transition periods
    private var _stackElements: [String : NavigationElement] = [:]

    init(initialPath: [String] = []) {
        self.stackPath = initialPath
        rectifyRootElement(path: initialPath)
        _stackPath = self.stackPath
    }

    @discardableResult func rectifyRootElement(path: [String]) -> Bool {
        // Rectify root state if set from outside
        if path.first != "" {
            stackPath = [ "" ] + path
            return false
        }
        return true
    }

    private func rectifyStack(path: [String], elements: [String : NavigationElement]) {
        var newStack: [NavigationElement] = []
        for tag in path {
            if let elem = elements[tag] {
                newStack.append(elem)
            }
            else {
                print("Path has a tag '\(tag)' which cannot be represented - truncating at last usable element")
                break
            }
        }
        stack = newStack
    }
}

struct NavigationStack<Content: View>: View {
    @ObservedObject var navState: NavigationState
    @State private var trigger: String = "humperdoo"    //HUMPERDOO! Chose something that would not conflict with empty root state - could probably do better with an enum

    init(_ navState: NavigationState, title: String, builder: @escaping () -> Content) {
        self.navState = navState
        self.navState.stackElements[""] = NavigationElement(tag: "", title: title, viewBuilder: { AnyView(builder()) })
    }

    var backButton: some View {
        Button(action: { self.navState.stackPath.removeLast() }) {
            Text("Back")
        }
    }

    var navigationHeader: some View {
        HStack {
            ViewBuilder.buildIf( navState.stack.count > 1 ? backButton : nil )
            Spacer()
            ViewBuilder.buildIf( navState.stack.last?.title != nil ? Text(navState.stack.last!.title) : nil )
            Spacer()
        }
        .frame(height: 40)
        .background(Color(.systemGray))
    }

    var currentNavElement: some View {
        return navState.stack.last!.viewBuilder()
    }

    var body: some View {
        VStack {
            // This is an effectively invisible element which primarily serves to force refreshes of the tree
            Text(trigger)
            .frame(width: 0, height: 0)
            .onReceive(navState.$stack, perform: { stack in
                self.trigger = stack.reduce("") { tag, elem in
                    return tag + "/" + elem.tag
                }
            })
            navigationHeader
            ViewBuilder.buildBlock(
                navState.stack.last != nil
                ? ViewBuilder.buildEither(first: currentNavElement)
                : ViewBuilder.buildEither(second: Text("The navigation stack is empty - this is odd"))
            )
        }
    }
}

struct NavigationDestination<Label: View, Destination: View>: View {

    @ObservedObject var navState: NavigationState
    var tag: String
    var label: () -> Label

    init(_ navState: NavigationState, tag: String, title: String, destination: @escaping () -> Destination, label: @escaping () -> Label) {
        self.navState = navState
        self.tag = tag
        self.label = label
        self.navState.stackElements[tag] = NavigationElement(tag: tag, title: title, viewBuilder: { AnyView(destination()) })
    }

    var body: some View {
        label()
        .onTapGesture {
            self.navState.stackPath.append(self.tag)
        }
    }
}

And some basic usage code

struct LandingPageView: View {

    @ObservedObject var navState: NavigationState

    var destinationA: some View {
        List {
            NavigationDestination(self.navState, tag: "aa", title: "AA", destination: { Text("AA") }) {
                Text("Go to AA")
            }
            NavigationDestination(self.navState, tag: "ab", title: "AB", destination: { Text("AB") }) {
                Text("Go to AB")
            }
        }
    }

    var destinationB: some View {
        List {
            NavigationDestination(self.navState, tag: "ba", title: "BA", destination: { Text("BA") }) {
                Text("Go to BA")
            }
            Button(action: { self.navState.stackPath = [ "a", "ab" ] }) {
                Text("Jump to AB")
            }
        }
    }

    var body: some View {
        NavigationStack(navState, title: "Start") {
            List {
                NavigationDestination(self.navState, tag: "a", title: "A", destination: { self.destinationA }) {
                    Text("Go to A")
                }
                NavigationDestination(self.navState, tag: "b", title: "B", destination: { self.destinationB }) {
                    Text("Go to B")
                }
            }
        }
    }
}