Fix HeaderContent not respecting bindings.

src/Wpf.Ui/Controls/NavigationView/NavigationView.AttachedProperties.cs

@@ -20,9 +20,19 @@ public partial class NavigationView
         "HeaderContent",
         typeof(object),
         typeof(NavigationView),
-        new FrameworkPropertyMetadata(null)
+        new FrameworkPropertyMetadata(null, OnHeaderContentChanged)
     );
 
+    private static void OnHeaderContentChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
+    {
+        if (d is not FrameworkElement frameworkElement)
+        {
+            return;
+        }
+
+        GetNavigationParent(frameworkElement)?.NotifyHeaderContentChanged(frameworkElement, e.NewValue);
+    }
+
     /// <summary>Helper for getting <see cref="HeaderContentProperty"/> from <paramref name="target"/>.</summary>
     /// <param name="target"><see cref="FrameworkElement"/> to read <see cref="HeaderContentProperty"/> from.</param>
     /// <returns>HeaderContent property value.</returns>

src/Wpf.Ui/Controls/NavigationView/NavigationView.Base.cs

@@ -63,6 +63,8 @@ public NavigationView()
 
     protected Dictionary<Type, INavigationViewItem> PageTypeNavigationViewsDictionary { get; } = [];
 
+    protected Dictionary<FrameworkElement, INavigationViewItem> PageToNavigationItemDictionary { get; } = [];
+
     private readonly ObservableCollection<string> _autoSuggestBoxItems = [];
     private readonly ObservableCollection<NavigationViewBreadcrumbItem> _breadcrumbBarItems = [];
 
@@ -126,6 +128,7 @@ protected virtual void OnUnloaded(object sender, RoutedEventArgs e)
 
         PageIdOrTargetTagNavigationViewsDictionary.Clear();
         PageTypeNavigationViewsDictionary.Clear();
+        PageToNavigationItemDictionary.Clear();
 
         ClearJournal();
 
@@ -508,5 +511,15 @@ private void NavigationStackOnCollectionChanged(object? sender, NotifyCollection
             default:
                 throw new ArgumentOutOfRangeException(nameof(e), e.Action, $"Unsupported action: {e.Action}");
         }
+
+        UpdateBreadcrumbContents();
+    }
+
+    private void UpdateBreadcrumbContents()
+    {
+        foreach (var breadcrumbItem in _breadcrumbBarItems)
+        {
+            breadcrumbItem.UpdateFromSource();
+        }
     }
 }

src/Wpf.Ui/Controls/NavigationView/NavigationView.Navigation.cs

@@ -215,9 +215,19 @@ private bool NavigateInternal(
 
         OnNavigated(pageInstance);
 
-        ApplyAttachedProperties(viewItem, pageInstance);
+        // Set up the association before setting DataContext
+        if (pageInstance is FrameworkElement frameworkElement)
+        {
+            // Set NavigationParent to allow HeaderContent property changes to find this NavigationView
+            frameworkElement.SetValue(NavigationParentProperty, this);
+        }
+
+        // Set DataContext first so bindings can resolve
         UpdateContent(pageInstance, dataContext);
 
+        // Apply properties after DataContext is set
+        ApplyAttachedProperties(viewItem, pageInstance);
+
         AddToNavigationStack(viewItem, addToNavigationStack, isBackwardsNavigated);
         AddToJournal(viewItem, isBackwardsNavigated);
 
@@ -325,14 +335,28 @@ private object GetNavigationItemInstance(INavigationViewItem viewItem)
             ?? throw new InvalidOperationException("Failed to create instance of the page");
     }
 
-    private static void ApplyAttachedProperties(INavigationViewItem viewItem, object pageInstance)
+    private void ApplyAttachedProperties(INavigationViewItem viewItem, object pageInstance)
     {
-        if (
-            pageInstance is FrameworkElement frameworkElement
-            && GetHeaderContent(frameworkElement) is { } headerContent
-        )
+        if (pageInstance is FrameworkElement frameworkElement)
+        {
+            // Store the association between page and navigation item
+            PageToNavigationItemDictionary[frameworkElement] = viewItem;
+
+            // Apply HeaderContent if already available
+            if (GetHeaderContent(frameworkElement) is { } headerContent)
+            {
+                viewItem.Content = headerContent;
+                UpdateBreadcrumbContents();
+            }
+        }
+    }
+
+    internal void NotifyHeaderContentChanged(FrameworkElement page, object? headerContent)
+    {
+        if (PageToNavigationItemDictionary.TryGetValue(page, out INavigationViewItem? navItem))
         {
-            viewItem.Content = headerContent;
+            navItem.Content = headerContent;
+            UpdateBreadcrumbContents();
         }
     }
 

src/Wpf.Ui/Controls/NavigationView/NavigationViewBreadcrumbItem.cs

@@ -9,15 +9,33 @@
 // ReSharper disable once CheckNamespace
 namespace Wpf.Ui.Controls;
 
-internal class NavigationViewBreadcrumbItem
+internal class NavigationViewBreadcrumbItem : DependencyObject
 {
+    public static readonly DependencyProperty ContentProperty = DependencyProperty.Register(
+        nameof(Content),
+        typeof(object),
+        typeof(NavigationViewBreadcrumbItem),
+        new PropertyMetadata(null));
+
     public NavigationViewBreadcrumbItem(INavigationViewItem item)
     {
-        Content = item.Content;
         PageId = item.Id;
+        SourceItem = item;
+        Content = item.Content;
     }
 
-    public object Content { get; }
+    public object Content
+    {
+        get => GetValue(ContentProperty);
+        set => SetValue(ContentProperty, value);
+    }
 
     public string PageId { get; }
+
+    public INavigationViewItem SourceItem { get; }
+
+    public void UpdateFromSource()
+    {
+        SetCurrentValue(ContentProperty, SourceItem.Content);
+    }
 }