Hide NavigationViewItem Chevron if Children is empty

Attach a CollectionChanged to ItemsRepeater ItemsViewSource
whenever the MenuItems or MenuItemsSource changes.
Add check to MenuItemsSource count when checking for children.

Fixes microsoft#2743

Author: MarkIvanDev

dev/NavigationView/NavigationViewItem.cpp

@@ -144,9 +144,16 @@ void NavigationViewItem::UpdateRepeaterItemsSource()
             }
             return MenuItems().as<winrt::IInspectable>();
         }();
+        m_itemsSourceViewChanged.revoke();
         repeater.ItemsSource(itemsSource);
+        m_itemsSourceViewChanged = repeater.ItemsSourceView().CollectionChanged(winrt::auto_revoke, { this, &NavigationViewItem::OnItemsSourceViewChanged });
     }
 }
+
+void NavigationViewItem::OnItemsSourceViewChanged(const winrt::IInspectable& sender, const winrt::NotifyCollectionChangedEventArgs& args)
+{
+    UpdateVisualStateForChevron();
+}
 
 winrt::UIElement NavigationViewItem::GetSelectionIndicator() const
 {
@@ -468,7 +475,7 @@ void NavigationViewItem::UpdateVisualStateForChevron()
 
 bool NavigationViewItem::HasChildren()
 {
-    return MenuItems().Size() > 0 || MenuItemsSource() != nullptr || HasUnrealizedChildren();
+    return MenuItems().Size() > 0 || (MenuItemsSource() != nullptr && m_repeater.get().ItemsSourceView().Count() > 0) || HasUnrealizedChildren();
 }
 
 bool NavigationViewItem::ShouldShowIcon()

dev/NavigationView/NavigationViewItem.h

@@ -100,6 +100,7 @@ class NavigationViewItem :
     bool HasChildren();
 
     void UpdateRepeaterItemsSource();
+    void OnItemsSourceViewChanged(const winrt::IInspectable& sender, const winrt::NotifyCollectionChangedEventArgs& args);
     void ReparentRepeater();
     void OnFlyoutClosing(const winrt::IInspectable& sender, const winrt::FlyoutBaseClosingEventArgs& args);
     void UpdateItemIndentation();
@@ -124,6 +125,7 @@ class NavigationViewItem :
 
     winrt::ItemsRepeater::ElementPrepared_revoker m_repeaterElementPreparedRevoker{};
     winrt::ItemsRepeater::ElementClearing_revoker m_repeaterElementClearingRevoker{};
+    winrt::ItemsSourceView::CollectionChanged_revoker m_itemsSourceViewChanged{};
 
     winrt::FlyoutBase::Closing_revoker m_flyoutClosingRevoker{};
     winrt::Control::IsEnabledChanged_revoker m_isEnabledChangedRevoker{};