reactor-navigation

name	reactor-navigation
description	Reactor navigation — `UseNavigation` hook, `NavigationHost` renderer, `NavigationView` sidebar, `TabView` tabs, route params, stack operations, page lifecycle, deep linking, transitions, caching. Use when building multi-page apps or wiring sidebar/tab navigation.

Navigation in Reactor

Reactor uses a stack-based navigation model with type-safe routes. You define routes as an enum, create a navigation handle with UseNavigation, and render the current page with NavigationHost. The system manages back/forward stacks, transitions, caching, and deep linking.

Quick reference

API	Purpose
UseNavigation(Route.Home)	Create a NavigationHandle<Route> (call once at root)
UseNavigation<Route>()	Retrieve the nearest ancestor's handle (child components)
NavigationHost(nav, route => ...)	Render the current page
NavigationView([items], content)	Sidebar navigation with icons
TabView(Tab(...), Tab(...))	Tab-based parallel navigation
UseNavigationLifecycle(...)	Page appear/disappear callbacks
UseSystemBackButton(nav, window)	Wire system back button to nav stack
DeepLinkMap<Route>	Map URI patterns to routes

1. Defining routes

Use an enum. Each value is a distinct page:

enum Route { Home, Settings, Profile, Details }

For routes that carry data, use a discriminated-union pattern with records:

abstract record Route
{
    public record Home : Route;
    public record Settings : Route;
    public record Details(int ItemId) : Route;
}

2. Basic navigation

class App : Component
{
    public override Element Render()
    {
        var nav = UseNavigation(Route.Home);

        return VStack(12,
            HStack(8,
                Button("Home", () => nav.Navigate(Route.Home)),
                Button("Settings", () => nav.Navigate(Route.Settings)),
                Button("Back", () => nav.GoBack()).IsEnabled(nav.CanGoBack)
            ),
            NavigationHost(nav, route => route switch
            {
                Route.Home     => Component<HomePage>(),
                Route.Settings => Component<SettingsPage>(),
                _ => TextBlock("Not found")
            })
        );
    }
}

Key points:

• UseNavigation(Route.Home) — call once at the root with the initial route.
• nav.Navigate(route) — pushes onto the back stack.
• nav.GoBack() / nav.GoForward() — stack navigation.
• NavigationHost(nav, route => ...) — renders the matched element.

3. Stack operations

Method	Effect
Navigate(route)	Push route onto back stack
GoBack()	Pop current, return to previous
GoForward()	Move forward (after going back)
Replace(route)	Swap current route without touching the stack
Reset(route)	Clear all stacks, start fresh
PopTo(predicate)	Pop until a matching route is found

Properties: CurrentRoute, CanGoBack, CanGoForward, BackStack, ForwardStack, Depth.

Use Reset for sign-out flows to prevent navigating back to authenticated pages.

4. NavigationView (sidebar)

var nav = UseNavigation(Route.Home);

return NavigationView(
    [
        NavItem("Home", icon: "Home", tag: "Home"),
        NavItem("Settings", icon: "Setting", tag: "Settings"),
        NavItem("Profile", icon: "Contact", tag: "Profile")
    ],
    content: NavigationHost(nav, route => route switch
    {
        Route.Home     => VStack(Heading("Home"), TextBlock("Welcome.")).Padding(24),
        Route.Settings => VStack(Heading("Settings"), TextBlock("Configure.")).Padding(24),
        Route.Profile  => VStack(Heading("Profile"), TextBlock("Your info.")).Padding(24),
        _ => TextBlock("Not found").Padding(24)
    })
);

NavItem(label, icon?, tag?) creates sidebar items. Icons are Segoe Fluent Icons names. The NavigationView handles selection state.

Manual wiring (without UseNavigation): SelectedTag and OnSelectionChanged are record properties — use with { }. For the settings item: set IsSettingsVisible = true and check args.IsSettingsSelected (not via tag). Use .Set(nv => nv.PaneDisplayMode = ...) for non-record properties.

5. TabView (parallel tabs)

Unlike stack navigation, tabs keep all content alive simultaneously:

return TabView(
    Tab("Documents", VStack(12,
        TextBlock("Your documents."),
        Button("New", () => { })).Padding(24)),
    Tab("Recent", TextBlock("Recently opened.").Padding(24)),
    Tab("Shared", TextBlock("Shared files.").Padding(24))
);

Use tabs when users switch freely between parallel workspaces.

6. Page lifecycle

UseNavigationLifecycle fires callbacks when a page appears or disappears:

UseNavigationLifecycle(
    onNavigatedTo: ctx => LoadData(ctx.PreviousRoute),
    onNavigatingFrom: ctx =>
    {
        if (hasUnsavedChanges) ctx.Cancel(); // prevent navigation
    },
    onNavigatedFrom: ctx => SaveDraft()
);

Callback	When
onNavigatedTo	After this page becomes active — fetch data, start timers
onNavigatingFrom	Before leaving — call ctx.Cancel() to block navigation
onNavigatedFrom	After leaving — save drafts, stop timers

7. Page transitions

Set Transition on NavigationHost:

NavigationHost(nav, route => ...) with
{
    Transition = NavigationTransition.DrillIn()
}

Transition	Effect
NavigationTransition.Entrance()	Slide up + fade in — the default, and what WinUI's Frame plays with no transition info
NavigationTransition.Slide()	Slide + fade — vertical unless you pass a direction
NavigationTransition.Fade()	Crossfade
NavigationTransition.DrillIn()	Scale + fade — use for list→detail
NavigationTransition.Spring()	Spring-physics slide
NavigationTransition.None	Instant swap

NavigationTransition.Default is an alias for Entrance(). Use Entrance() when you mean the motion; use Default only when you mean "whatever the framework default is".

GoBack automatically reverses direction. Transitions run on the compositor thread.

8. Deep linking

DeepLinkMap maps URI patterns to route constructors:

var map = UseMemo(() => new DeepLinkMap<Route>()
    .Map("/", _ => Route.Home)
    .Map("/settings", _ => Route.Settings)
    .Map("/users/{id:int}/posts/{postId:int}", args =>
    {
        var userId = args.Get<int>("id");
        var postId = args.Get<int>("postId");
        return Route.Details;
    }, backStackFactory: () => new[] { Route.Home }));

// Resolve from activation URI:
map.Resolve(uri);

Pattern segments:

Segment	Matches
/literal	Exact match
/{param}	String capture
/{param:int}	Typed capture (int, long, bool, Guid)
/{param?}	Optional parameter
/{**}	Wildcard — remaining path
?key=value	Query string parameters

backStackFactory builds a synthetic back stack so GoBack works after deep-linked entry.

9. Page caching

NavigationHost(nav, route => ...) with
{
    CacheMode = NavigationCacheMode.Enabled,
    CacheSize = 5
}

Cache mode	Behavior
Disabled	Always unmount/remount (default)
Enabled	LRU cache up to CacheSize entries
Required	Always cached, never evicted

Caching preserves scroll position, text input, and component state.

10. State serialization

var state = nav.GetState();         // NavigationState<TRoute> snapshot
nav.SetState(state);                // restore stacks + fire Navigated(Reset)

Reactor returns a plain NavigationState<TRoute> POCO and lets you pick the storage format. For JSON persistence pair the snapshot with a JsonSerializerContext (AOT-safe):

[JsonSerializable(typeof(NavigationState<AppRoute>))]
partial class AppJsonContext : JsonSerializerContext { }

var json = JsonSerializer.Serialize(nav.GetState(), AppJsonContext.Default.NavigationStateAppRoute);
// later…
nav.SetState(JsonSerializer.Deserialize(json, AppJsonContext.Default.NavigationStateAppRoute)!);

Use for persisting navigation across app restarts.

11. System back button

UseSystemBackButton(nav, window);

Wires the Windows title-bar back button and hardware back button to your navigation stack automatically.

Critical gotchas

1. Call UseNavigation(initial) once at the root. Children retrieve the same handle via UseNavigation<Route>() (no initial value) through context.
2. Use enums for routes. Compile-time safety — can't navigate to a non-existent route.
3. Use Reset for sign-out. Clears the stack so users can't go back.
4. DrillIn for list→detail. Signals hierarchy; pairs with connected animation.
5. ctx.Cancel() in onNavigatingFrom — the only way to guard against unsaved-changes navigation.
6. Don't forget backStackFactory in deep links. Without it, GoBack does nothing after a deep-linked entry.

Threading

UseNavigation mutators are thread-safe by default (issue #234). The handle captures the UI thread when it is created, so calling Navigate, GoBack, GoForward, Replace, Reset, PopTo, or SetState from a Task.Run, a timer, or after await … ConfigureAwait(false) auto-marshals the operation back onto the captured dispatcher — no threadSafe: flag and no manual DispatcherQueue.TryEnqueue needed:

await Task.Run(async () => {
    var itemId = await LoadItemIdAsync();
    nav.Navigate(new Route.Details(itemId)); // marshals onto the UI thread automatically
});

This mirrors the UseState / UseReducer contract. Two caveats:

• No live dispatcher → loud throw. Off-thread calls in a headless or unit-test context (no ReactorApp.UIDispatcher), or after the dispatcher has shut down, throw InvalidOperationException instead of silently corrupting the back/forward stacks. On the UI thread the call runs inline.
• Off-thread bool means "scheduled", not "navigated". When a mutator marshals, its return value reports that the operation was enqueued, not that the navigation ultimately succeeded. Don't branch on it from a background thread.