Switch from using PrepareContainerForItemOverride to IsItemItsOwnCont…

…ainerOverride.

dev/NavigationView/NavigationViewList.cpp

@@ -26,6 +26,15 @@ bool NavigationViewList::IsItemItsOwnContainerOverride(winrt::IInspectable const
     bool isItemItsOwnContainerOverride = false;
     if (args)
     {
+        // This validation is only relevant outside of the Windows build where WUXC and MUXC have distinct types.
+#if !BUILD_WINDOWS
+        // Certain items are disallowed in a NavigationView's items list. Check for them.
+        if (args.try_as<winrt::Windows::UI::Xaml::Controls::NavigationViewItemBase>())
+        {
+            throw winrt::hresult_invalid_argument(L"MenuItems contains a Windows.UI.Xaml.Controls.NavigationViewItem. This control requires that the NavigationViewItems be of type Microsoft.UI.Xaml.Controls.NavigationViewItem.");
+        }
+#endif
+
         auto nvib = args.try_as<winrt::NavigationViewItemBase>();
         if (nvib && nvib != m_lastItemCalledInIsItemItsOwnContainerOverride.get())
         {
@@ -57,15 +66,6 @@ void NavigationViewList::PrepareContainerForItemOverride(winrt::DependencyObject
         winrt::get_self<NavigationViewItem>(itemContainer)->ClearIsContentChangeHandlingDelayedForTopNavFlag();
     }
 
-    // The following validation is only relevant outside of the Windows build where WUXC and MUXC have distinct types.
-#if !BUILD_WINDOWS
-    // Certain items are disallowed in a NavigationView's items list. Check for them.
-    if (element.try_as<winrt::Windows::UI::Xaml::Controls::NavigationViewItemBase>())
-    {
-        throw winrt::hresult_invalid_argument(L"MenuItems contains a Windows.UI.Xaml.Controls.NavigationViewItem. This control requires that the NavigationViewItems be of type Microsoft.UI.Xaml.Controls.NavigationViewItem.");
-    }
-#endif
-
     __super::PrepareContainerForItemOverride(element, item);
 }