Meditor SourceGen doesn't work for our needs right now, so let's build something on top of their library that allows us to do manual registration for now.

Controls/Avalonia/IconElement/ContentIcon.cs

@@ -2,6 +2,7 @@
 using Avalonia.Controls;
 using Avalonia.Controls.Templates;
 using Avalonia.LogicalTree;
+using Avalonia.Metadata;
 
 namespace Toolkit.Controls.Avalonia;
 
@@ -10,13 +11,14 @@ public class ContentIcon : FluentAvalonia.UI.Controls.FAIconElement
     public static readonly StyledProperty<IDataTemplate> IconTemplateProperty =
         AvaloniaProperty.Register<ContentIcon, IDataTemplate>("IconTemplate");
 
-    public static readonly StyledProperty<object> IconProperty = 
-        AvaloniaProperty.Register<ContentIcon, object>("Icon");
+    public static readonly StyledProperty<object> ContentProperty = 
+        AvaloniaProperty.Register<ContentIcon, object>("Content");
 
-    public object Icon
+    [Content]
+    public object Content
     {
-        get => GetValue(IconProperty);
-        set => SetValue(IconProperty, value);
+        get => GetValue(ContentProperty);
+        set => SetValue(ContentProperty, value);
     }
 
     private ContentControl? content;
@@ -64,7 +66,7 @@ public class ContentIcon : FluentAvalonia.UI.Controls.FAIconElement
     {
         content = new ContentControl();
 
-        content.Bind(ContentControl.ContentProperty, this.GetBindingObservable(IconProperty));
+        content.Bind(ContentControl.ContentProperty, this.GetBindingObservable(ContentProperty));
         content.Bind(ContentControl.ContentTemplateProperty, this.GetBindingObservable(IconTemplateProperty));
 
         LogicalChildren.Add(content);

Controls/Avalonia/NavigationView/NavigationViewItem.cs

@@ -1,8 +1,34 @@
-using Avalonia.Styling;
+using Avalonia.Controls.Primitives;
+using Avalonia.Styling;
+using Avalonia.VisualTree;
+using FluentAvalonia.UI.Controls;
 
 namespace Toolkit.Controls.Avalonia;
 
 public class NavigationViewItem : FluentAvalonia.UI.Controls.NavigationViewItem, IStyleable
 {
+    private NavigationView? navigationView;
+
+    public event EventHandler<NavigationViewItemInvokedEventArgs> Invoked;
+
     Type IStyleable.StyleKey => typeof(FluentAvalonia.UI.Controls.NavigationViewItem);
+
+    protected override void OnApplyTemplate(TemplateAppliedEventArgs args)
+    {
+        navigationView = this.FindAncestorOfType<NavigationView>();
+        if (navigationView is not null)
+        {
+            navigationView.ItemInvoked += OnItemInvoked;
+        }
+
+        base.OnApplyTemplate(args);
+    }
+
+    private void OnItemInvoked(object? sender, NavigationViewItemInvokedEventArgs args)
+    {
+        if (args.InvokedItemContainer == this)
+        {
+            Invoked?.Invoke(this, args);
+        }
+    }
 }