SettingsExpander fixes

Toolkit.UI.Controls.Avalonia/SettingsExpander/SettingsExpanderItem.cs

@@ -1,4 +1,5 @@
 using Avalonia;
+using Avalonia.Controls;
 using Avalonia.Controls.Templates;
 
 namespace Toolkit.UI.Controls.Avalonia;
@@ -12,6 +13,27 @@ public class SettingsExpanderItem :
     public static readonly StyledProperty<IDataTemplate> ActionTemplateProperty =
         AvaloniaProperty.Register<SettingsExpanderItem, IDataTemplate>(nameof(ActionTemplate));
 
+    public static readonly StyledProperty<object> IconProperty =
+        AvaloniaProperty.Register<SettingsExpanderItem, object>(nameof(Icon));
+
+    public static readonly StyledProperty<IDataTemplate> IconTemplateProperty =
+        AvaloniaProperty.Register<SettingsExpanderItem, IDataTemplate>(nameof(IconTemplate));
+
+    protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
+    {
+        base.OnPropertyChanged(change);
+
+        if (change.Property == IconProperty || change.Property == IconTemplateProperty)
+        {
+            UpdateIcon();
+        }
+    }
+
+    private void UpdateIcon()
+    {
+        PseudoClasses.Set(":icon", Icon is not null || IconTemplate is not null);
+    }
+
     public object Action
     {
         get => GetValue(ActionProperty);
@@ -24,6 +46,18 @@ public class SettingsExpanderItem :
         set => SetValue(ActionTemplateProperty, value);
     }
 
+    public object Icon
+    {
+        get => GetValue(IconProperty);
+        set => SetValue(IconProperty, value);
+    }
+
+    public IDataTemplate IconTemplate
+    {
+        get => GetValue(IconTemplateProperty);
+        set => SetValue(IconTemplateProperty, value);
+    }
+
     protected override Type StyleKeyOverride =>
         typeof(SettingsExpanderItem);
 }