add partial codes

src/Shared/HandyControl_Shared/Controls/PropertyGrid/PropertyItemsControl.cs

@@ -0,0 +1,9 @@
+using System.Windows.Controls;
+
+namespace HandyControl.Controls
+{
+    public class PropertyItemsControl : ItemsControl
+    {
+        protected override bool IsItemItsOwnContainerOverride(object item) => item is PropertyItem;
+    }
+}