UI

Toolkit.Foundation/IProvider.cs

@@ -9,3 +9,8 @@ public interface IProvider<TService>
 {
     TService? Get();
 }
+
+public interface ISelectable
+{
+    bool Selected { get; set; }
+}

Toolkit.Foundation/ObservableCollectionViewModel.cs

@@ -97,7 +97,7 @@ public partial class ObservableCollectionViewModel<TViewModel> :
 
     public TViewModel this[int index]
     {
-        get => collection[index];
+        get => Count > 0 ? collection[index] : default;
         set => SetItem(index, value);
     }
 

Toolkit.UI.Avalonia/AttachedBehaviour.cs

@@ -2,7 +2,7 @@
 
 namespace Toolkit.UI.Avalonia;
 
-public class AttachedBehavior : Trigger
+public class AttachedBehaviour : Trigger
 {
     protected override void OnAttachedToVisualTree()
     {

Toolkit.UI.Avalonia/KeyBindingTriggerBehaviour.cs

@@ -5,12 +5,12 @@ using System.Windows.Input;
 
 namespace Toolkit.UI.Avalonia;
 
-public class KeyBindingTriggerBehavior :
+public class KeyBindingTriggerBehaviour :
     Trigger<InputElement>,
     ICommand
 {
     public static readonly StyledProperty<KeyGesture> GestureProperty =
-        AvaloniaProperty.Register<KeyBindingTriggerBehavior, KeyGesture>(nameof(Gesture));
+        AvaloniaProperty.Register<KeyBindingTriggerBehaviour, KeyGesture>(nameof(Gesture));
 
     public KeyGesture Gesture
     {
@@ -24,7 +24,7 @@ public class KeyBindingTriggerBehavior :
     {
         if (Gesture is not null)
         {
-            KeyBinding keyBinding = new KeyBinding
+            KeyBinding keyBinding = new()
             {
                 Gesture = Gesture,
                 Command = this

Toolkit.UI.Avalonia/NavigationViewItemInvokedBehaviour.cs

@@ -0,0 +1,86 @@
+using Avalonia;
+using Avalonia.VisualTree;
+using Avalonia.Xaml.Interactivity;
+using FluentAvalonia.Core;
+using System.Collections;
+using Toolkit.UI.Controls.Avalonia;
+using ISelectable = Toolkit.Foundation.ISelectable;
+
+namespace Toolkit.UI.Avalonia;
+
+public class NavigationViewItemInvokedBehaviour : Trigger
+{
+    public static readonly StyledProperty<bool> SelectsChildOnInvokedProperty =
+        AvaloniaProperty.Register<NavigationViewItemInvokedBehaviour, bool>(nameof(SelectsChildOnInvoked));
+
+    private NavigationView? navigationView;
+
+    public event TypedEventHandler<NavigationViewItem, EventArgs>? Invoked;
+
+    public bool SelectsChildOnInvoked
+    {
+        get => GetValue(SelectsChildOnInvokedProperty);
+        set => SetValue(SelectsChildOnInvokedProperty, value);
+    }
+
+    protected override void OnAttached()
+    {
+        if (AssociatedObject is NavigationViewItem navigationViewItem)
+        {
+            navigationViewItem.AttachedToVisualTree += OnAttachedToVisualTree;
+        }
+
+        base.OnAttached();
+    }
+
+    protected override void OnDetachedFromVisualTree()
+    {
+        if (navigationView is not null)
+        {
+            navigationView.ItemInvoked -= OnItemInvoked;
+        }
+
+        base.OnDetachedFromVisualTree();
+    }
+
+    private void OnAttachedToVisualTree(object? sender,
+        VisualTreeAttachmentEventArgs args)
+    {
+        if (AssociatedObject is NavigationViewItem navigationViewItem)
+        {
+            navigationViewItem.AttachedToVisualTree -= OnAttachedToVisualTree;
+            SetupNavigationView();
+        }
+    }
+
+    private void OnItemInvoked(object? sender,
+        FluentAvalonia.UI.Controls.NavigationViewItemInvokedEventArgs args)
+    {
+        if (AssociatedObject is NavigationViewItem navigationViewItem)
+        {
+            if (args.InvokedItemContainer == AssociatedObject)
+            {
+                Interaction.ExecuteActions(AssociatedObject, Actions, null);
+                if (!navigationViewItem.IsChildSelected && navigationViewItem.MenuItemsSource is IList collection)
+                {
+                    if (collection is { Count: > 0 } && collection[0] is ISelectable selectable)
+                    {
+                        selectable.Selected = true;
+                    }
+                }
+            }
+        }
+    }
+
+    private void SetupNavigationView()
+    {
+        if (AssociatedObject is NavigationViewItem navigationViewItem)
+        {
+            if (navigationViewItem.GetVisualAncestors().OfType<NavigationView>().FirstOrDefault() is NavigationView navigationView)
+            {
+                this.navigationView = navigationView;
+                navigationView.ItemInvoked += OnItemInvoked;
+            }
+        }
+    }
+}

Toolkit.UI.Avalonia/SelectNavigationViewItemAction.cs

@@ -0,0 +1,48 @@
+using Avalonia;
+using Avalonia.Threading;
+using Avalonia.Xaml.Interactivity;
+using System.Collections;
+using System.Collections.ObjectModel;
+using System.Collections.Specialized;
+using Toolkit.Foundation;
+using Toolkit.UI.Controls.Avalonia;
+
+namespace Toolkit.UI.Avalonia;
+
+public class SelectNavigationViewItemAction :
+    AvaloniaObject,
+    IAction
+{
+    public object? Execute(object? sender, object? parameter)
+    {
+        if (sender is NavigationViewItem navigationViewItem)
+        {
+            Dispatcher.UIThread.Post(() =>
+            {
+                if (navigationViewItem.MenuItemsSource is IList collection)
+                {
+                    if (collection is { Count: > 0 } && collection[0] is ISelectable selectable)
+                    {
+                        selectable.Selected = true;
+                    }
+                }
+            }, DispatcherPriority.ContextIdle);
+        }
+
+        if (sender is NavigationView navigationView)
+        {
+            Dispatcher.UIThread.Post(() =>
+            {
+                if (navigationView.MenuItemsSource is IList collection)
+                {
+                    if (collection is { Count: > 0 } && collection[0] is ISelectable selectable)
+                    {
+                        selectable.Selected = true;
+                    }
+                }
+            }, DispatcherPriority.ContextIdle);
+        }
+
+        return true;
+    }
+}

Toolkit.UI.Avalonia/Toolkit.UI.Avalonia.csproj

@@ -10,5 +10,6 @@
 	</ItemGroup>
 	<ItemGroup>
 	  <ProjectReference Include="..\Toolkit.Foundation\Toolkit.Foundation.csproj" />
+	  <ProjectReference Include="..\Toolkit.UI.Controls.Avalonia\Toolkit.UI.Controls.Avalonia.csproj" />
 	</ItemGroup>
 </Project>