Hide NavigationViewItem Chevron if Children is empty (microsoft/micro…

…soft-ui-xaml#2759)
Kinnara · Jul 3, 2020 · 8857b72 · 8857b72
1 parent 0fa6b69
commit 8857b72
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diff --git a/ModernWpf.Controls/NavigationView/NavigationViewItem.cs b/ModernWpf.Controls/NavigationView/NavigationViewItem.cs
@@ -2,6 +2,7 @@
 // Licensed under the MIT License. See LICENSE in the project root for license information.
 
 using System.Collections.ObjectModel;
+using System.Collections.Specialized;
 using System.Diagnostics;
 using System.Windows;
 using System.Windows.Automation.Peers;
@@ -169,10 +170,17 @@ object init()
                     }
                     itemsSource = init();
                 }
+                m_itemsSourceViewCollectionChangedRevoker?.Revoke();
                 repeater.ItemsSource = itemsSource;
+                m_itemsSourceViewCollectionChangedRevoker = new ItemsSourceView.CollectionChanged_revoker(repeater.ItemsSourceView, OnItemsSourceViewChanged);
             }
         }
 
+        private void OnItemsSourceViewChanged(object sender, NotifyCollectionChangedEventArgs args)
+        {
+            UpdateVisualStateForChevron();
+        }
+
         internal UIElement GetSelectionIndicator()
         {
             var selectIndicator = m_helper.GetSelectionIndicator();
@@ -493,7 +501,7 @@ void UpdateVisualStateForChevron()
 
         internal bool HasChildren()
         {
-            return MenuItems.Count > 0 || MenuItemsSource != null || HasUnrealizedChildren;
+            return MenuItems.Count > 0 || (MenuItemsSource != null && m_repeater.ItemsSourceView.Count > 0) || HasUnrealizedChildren;
         }
 
         bool ShouldShowIcon()
@@ -881,6 +889,7 @@ void UnhookEventsAndClearFields()
             m_repeaterElementPreparedRevoker?.Revoke();
             m_repeaterElementClearingRevoker?.Revoke();
             IsEnabledChanged -= OnIsEnabledChanged;
+            m_itemsSourceViewCollectionChangedRevoker?.Revoke();
 
             m_rootGrid = null;
             m_navigationViewItemPresenter = null;
@@ -895,6 +904,7 @@ void UnhookEventsAndClearFields()
 
         ItemsRepeaterElementPreparedRevoker m_repeaterElementPreparedRevoker;
         ItemsRepeaterElementClearingRevoker m_repeaterElementClearingRevoker;
+        ItemsSourceView.CollectionChanged_revoker m_itemsSourceViewCollectionChangedRevoker;
 
         FlyoutBaseClosingRevoker m_flyoutClosingRevoker;
 

diff --git a/ModernWpf.Controls/Repeater/ItemsRepeater/ItemsSource/ItemsSourceView.cs b/ModernWpf.Controls/Repeater/ItemsRepeater/ItemsSource/ItemsSourceView.cs
@@ -88,5 +88,24 @@ internal virtual int IndexOfCore(object value)
         }
 
         private int m_cachedSize = -1;
+
+        internal class CollectionChanged_revoker : EventRevoker<ItemsSourceView, NotifyCollectionChangedEventHandler>
+        {
+            public CollectionChanged_revoker(ItemsSourceView source, NotifyCollectionChangedEventHandler handler) : base(source, handler)
+            {
+            }
+
+            protected override void AddHandler(ItemsSourceView source, NotifyCollectionChangedEventHandler handler)
+            {
+                source.CollectionChanged += handler;
+            }
+
+            protected override void RemoveHandler(ItemsSourceView source, NotifyCollectionChangedEventHandler handler)
+            {
+                source.CollectionChanged -= handler;
+            }
+        }
     }
+
+
 }
diff --git a/ModernWpf/Common/EventRevoker.cs b/ModernWpf/Common/EventRevoker.cs
@@ -12,6 +12,7 @@ internal abstract class EventRevoker<TSource, TDelegate>
         public EventRevoker(TSource source, TDelegate handler)
         {
             _source = new WeakReference<TSource>(source);
+            _handler = new WeakReference<TDelegate>(handler);
             AddHandler(source, handler);
         }
 

diff --git a/test/ModernWpfTestApp/ApiTests/NavigationViewTests.cs b/test/ModernWpfTestApp/ApiTests/NavigationViewTests.cs
@@ -798,5 +798,67 @@ public void VerifyNavigationViewItemInFooterDoesNotCrash()
                 Verify.IsTrue(true);
             });
         }
+
+        [TestMethod]
+        public void VerifyExpandCollapseChevronVisibility()
+        {
+            NavigationView navView = null;
+            NavigationViewItem parentItem = null;
+            ObservableCollection<string> children = null;
+
+            RunOnUIThread.Execute(() =>
+            {
+                navView = new NavigationView();
+                Content = navView;
+
+                children = new ObservableCollection<string>();
+                parentItem = new NavigationViewItem() { Content = "ParentItem", MenuItemsSource = children };
+
+                navView.MenuItems.Add(parentItem);
+
+                navView.Width = 1008; // forces the control into Expanded mode so that the menu renders
+                Content.UpdateLayout(true);
+
+                UIElement chevronUIElement = (UIElement)VisualTreeUtils.FindVisualChildByName(parentItem, "ExpandCollapseChevron");
+                Verify.IsTrue(chevronUIElement.Visibility == Visibility.Collapsed, "chevron should have been collapsed as NavViewItem has no children");
+
+                // Add a child to parentItem through the MenuItemsSource API. This should make the chevron visible.
+                children.Add("Child 1");
+                Content.UpdateLayout(true);
+
+                Verify.IsTrue(chevronUIElement.Visibility == Visibility.Visible, "chevron should have been visible as NavViewItem now has children");
+
+                // Remove all children of parentItem. This should collapse the chevron
+                children.Clear();
+                Content.UpdateLayout(true);
+
+                Verify.IsTrue(chevronUIElement.Visibility == Visibility.Collapsed, "chevron should have been collapsed as NavViewItem no longer has children");
+
+                // Add a child to parentItem and set the MenuItemsSource as null. This should collapse the chevron
+                children.Add("Child 2");
+                Content.UpdateLayout(true);
+
+                // we are doing this so that when we set MenuItemsSource as null, we can check if the chevron's visibility really changes
+                Verify.IsTrue(chevronUIElement.Visibility == Visibility.Visible, "chevron should have been visible as NavViewItem now has children");
+
+                parentItem.MenuItemsSource = null;
+                Content.UpdateLayout(true);
+
+                Verify.IsTrue(chevronUIElement.Visibility == Visibility.Collapsed, "chevron should have been collapsed as NavViewItem no longer has children");
+
+                // Add a child to parentItem through the MenuItems API. This should make the chevron visible.
+                parentItem.MenuItems.Add(new NavigationViewItem() { Content = "Child 3" });
+                Content.UpdateLayout(true);
+
+                Verify.IsTrue(chevronUIElement.Visibility == Visibility.Visible, "chevron should have been visible as NavViewItem now has children");
+
+                // Remove all children of parentItem. This should collapse the chevron
+                parentItem.MenuItems.Clear();
+                Content.UpdateLayout(true);
+
+                Verify.IsTrue(chevronUIElement.Visibility == Visibility.Collapsed, "chevron should have been collapsed as NavViewItem no longer has children");
+            });
+        }
+
     }
 }