chore: add avalonia TabControl demo.

src/Shared/HandyControl_Shared/Tools/StyleSelector/TabItemCapsuleStyleSelector.cs

@@ -8,27 +8,28 @@ public class TabItemCapsuleStyleSelector : StyleSelector
 {
     public override Style SelectStyle(object item, DependencyObject container)
     {
-        if (container is TabItem tabItem && VisualHelper.GetParent<TabControl>(tabItem) is { } tabControl)
+        if (container is not TabItem tabItem || VisualHelper.GetParent<TabControl>(tabItem) is not { } tabControl)
         {
-            var count = tabControl.Items.Count;
-            if (count == 1)
-            {
-                return ResourceHelper.GetResourceInternal<Style>(ResourceToken.TabItemCapsuleSingle);
-            }
-
-            var index = tabControl.ItemContainerGenerator.IndexFromContainer(tabItem);
-            return index == 0
-                ? ResourceHelper.GetResourceInternal<Style>(
-                    tabControl.TabStripPlacement == Dock.Top || tabControl.TabStripPlacement == Dock.Bottom
-                        ? ResourceToken.TabItemCapsuleHorizontalFirst
-                        : ResourceToken.TabItemCapsuleVerticalFirst)
-                : ResourceHelper.GetResourceInternal<Style>(index == count - 1
-                    ? tabControl.TabStripPlacement == Dock.Top || tabControl.TabStripPlacement == Dock.Bottom
-                        ? ResourceToken.TabItemCapsuleHorizontalLast
-                        : ResourceToken.TabItemCapsuleVerticalLast
-                    : ResourceToken.TabItemCapsuleDefault);
+            return null;
         }
 
-        return null;
+        var count = tabControl.Items.Count;
+        if (count == 1)
+        {
+            return ResourceHelper.GetResourceInternal<Style>(ResourceToken.TabItemCapsuleSingle);
+        }
+
+        var index = tabControl.ItemContainerGenerator.IndexFromContainer(tabItem);
+        return index == 0
+            ? ResourceHelper.GetResourceInternal<Style>(
+                tabControl.TabStripPlacement is Dock.Top or Dock.Bottom
+                    ? ResourceToken.TabItemCapsuleHorizontalFirst
+                    : ResourceToken.TabItemCapsuleVerticalFirst)
+            : ResourceHelper.GetResourceInternal<Style>(index == count - 1
+                ? tabControl.TabStripPlacement is Dock.Top or Dock.Bottom
+                    ? ResourceToken.TabItemCapsuleHorizontalLast
+                    : ResourceToken.TabItemCapsuleVerticalLast
+                : ResourceToken.TabItemCapsuleDefault);
+
     }
 }