feat: stop changing selection after checking canselect. revert focus change in this case.

src/Ursa/Controls/NavMenu/NavMenu.cs

@@ -191,10 +191,10 @@ public class NavMenu : ItemsControl, ICustomKeyboardNavigation
     }
     
     
-    public static readonly RoutedEvent<SelectionChangedEventArgs> SelectionChangingEvent =
+    public static readonly RoutedEvent<SelectionChangingEventArgs> SelectionChangingEvent =
-        RoutedEvent.Register<NavMenu, SelectionChangedEventArgs>(nameof(SelectionChanging), RoutingStrategies.Bubble);
+        RoutedEvent.Register<NavMenu, SelectionChangingEventArgs>(nameof(SelectionChanging), RoutingStrategies.Bubble);
 
-    public event EventHandler SelectionChanging
+    public event EventHandler<SelectionChangingEventArgs> SelectionChanging
     {
         add => AddHandler(SelectionChangingEvent, value);
         remove => RemoveHandler(SelectionChangingEvent, value);
@@ -512,6 +512,12 @@ public class NavMenu : ItemsControl, ICustomKeyboardNavigation
             Source = this,
         };
         RaiseEvent(args);
-        return args.CanSelect;
+        var result =  args.CanSelect;
+        if (result == false)
+        {
+            var container = GetContainerForItem(SelectedItem);
+            container?.Focus(NavigationMethod.Directional);
+        }
+        return result;
     }
 }

src/Ursa/Controls/NavMenu/NavMenuItem.cs

@@ -381,6 +381,10 @@ public class NavMenuItem : HeaderedItemsControl
 
     internal void SelectItem(NavMenuItem item)
     {
+        if (item == this && RootMenu?.CanChangeSelection(item) != true)
+        {
+            return;
+        }
         SetCurrentValue(IsSelectedProperty, item == this);
         SetCurrentValue(IsHighlightedProperty, true);
 

src/Ursa/Controls/NavMenu/SelectionChangingEventArgs.cs

@@ -6,19 +6,19 @@ namespace Ursa.Controls;
 public class SelectionChangingEventArgs: RoutedEventArgs
 {
     /// <summary>Gets the items that were added to the selection.</summary>
-    public IList AddedItems { get; }
+    public IList NewItems { get; }
 
     /// <summary>Gets the items that were removed from the selection.</summary>
-    public IList RemovedItems { get; }
+    public IList OldItems { get; }
     
     /// <summary>
     /// Gets or sets a value indicating whether the selection can be changed. If set to <c>false</c>, the selection will not change.
     /// </summary>
     public bool CanSelect { get; set; } = true;
     
-    public SelectionChangingEventArgs(RoutedEvent routedEvent, IList removedItems, IList addedItems): base(routedEvent)
+    public SelectionChangingEventArgs(RoutedEvent routedEvent, IList oldItems, IList newItems): base(routedEvent)
     {
-        RemovedItems = removedItems;
+        OldItems = oldItems;
-        AddedItems = addedItems;
+        NewItems = newItems;
     }
 }