Handle deselecting removed items...

in SelectingItemsControl.

Perspex.Controls/ItemsControl.cs

@@ -126,7 +126,7 @@ namespace Perspex.Controls
 
             if (incc != null)
             {
-                incc.CollectionChanged -= this.ItemsCollectionChanged;
+                incc.CollectionChanged += this.ItemsCollectionChanged;
             }
         }
 

Perspex.Controls/Primitives/SelectingItemsControl.cs

@@ -11,6 +11,8 @@ namespace Perspex.Controls.Primitives
     using Perspex.VisualTree;
     using System;
     using System.Linq;
+    using System.Collections;
+    using System.Collections.Specialized;
 
     public abstract class SelectingItemsControl : ItemsControl
     {
@@ -66,6 +68,42 @@ namespace Perspex.Controls.Primitives
             set { this.SetValue(SelectedItemProperty, value); }
         }
 
+        protected override void ItemsChanged(IEnumerable oldValue, IEnumerable newValue)
+        {
+            base.ItemsChanged(oldValue, newValue);
+
+            var selected = this.SelectedItem;
+
+            if (selected != null)
+            {
+                if (newValue == null || !newValue.Contains(selected))
+                {
+                    this.SelectedItem = null;
+                }
+            }
+        }
+
+        protected override void ItemsCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
+        {
+            base.ItemsCollectionChanged(sender, e);
+
+            var selected = this.SelectedItem;
+
+            switch (e.Action)
+            {
+                case NotifyCollectionChangedAction.Remove:
+                case NotifyCollectionChangedAction.Reset:
+                    if (e.OldItems.Contains(selected))
+                    {
+                        this.SelectedItem = null;
+                    }
+                    break;
+                case NotifyCollectionChangedAction.Move:
+                    this.SelectedItem = this.Items.IndexOf(selected);
+                    break;
+            }
+        }
+
         protected virtual void MoveSelection(FocusNavigationDirection direction)
         {
             var panel = this.Presenter?.Panel as INavigablePanel;

Perspex.Controls/Utils/IEnumerableUtils.cs

@@ -13,6 +13,11 @@ namespace Perspex.Controls.Utils
 
     internal static class IEnumerableUtils
     {
+        public static bool Contains(this IEnumerable items, object item)
+        {
+            return items.IndexOf(item) != -1;
+        }
+
         public static int Count(this IEnumerable items)
         {
             Contract.Requires<ArgumentNullException>(items != null);

Tests/Perspex.Controls.UnitTests/Primitives/SelectingItemsControlTests.cs

@@ -6,6 +6,7 @@
 
 namespace Perspex.Controls.Primitives.UnitTests
 {
+    using Perspex.Collections;
     using Perspex.Controls.Presenters;
     using Perspex.Controls.Primitives;
     using Perspex.Input;
@@ -173,6 +174,60 @@ namespace Perspex.Controls.Primitives.UnitTests
             target.SelectedItem = new Item();
         }
 
+        [Fact]
+        public void Clearing_Items_Should_Clear_Selection()
+        {
+            var items = new PerspexList<Item>
+            {
+                new Item(),
+                new Item(),
+            };
+
+            var target = new Target
+            {
+                Items = items,
+                Template = this.Template(),
+            };
+
+            target.ApplyTemplate();
+            target.SelectedIndex = 1;
+
+            Assert.Equal(items[1], target.SelectedItem);
+            Assert.Equal(1, target.SelectedIndex);
+
+            target.Items = null;
+
+            Assert.Equal(null, target.SelectedItem);
+            Assert.Equal(-1, target.SelectedIndex);
+        }
+
+        [Fact]
+        public void Removing_Selected_Item_Should_Clear_Selection()
+        {
+            var items = new PerspexList<Item>
+            {
+                new Item(),
+                new Item(),
+            };
+
+            var target = new Target
+            {
+                Items = items,
+                Template = this.Template(),
+            };
+
+            target.ApplyTemplate();
+            target.SelectedIndex = 1;
+
+            Assert.Equal(items[1], target.SelectedItem);
+            Assert.Equal(1, target.SelectedIndex);
+
+            items.RemoveAt(1);
+
+            Assert.Equal(null, target.SelectedItem);
+            Assert.Equal(-1, target.SelectedIndex);
+        }
+
         [Fact]
         public void PointerPressed_Event_Should_Be_Handled()
         {