Make SelectedItems a plain IList

As IList<T> is not covariant.

samples/BindingTest/ViewModels/MainWindowViewModel.cs

@@ -18,7 +18,7 @@ namespace BindingTest.ViewModels
                     StringValue = "Item " + x
                 }));
 
-            SelectedItems = new ObservableCollection<int> { 4, 6 };
+            SelectedItems = new ObservableCollection<TestItem>();
 
             ShuffleItems = ReactiveCommand.Create();
             ShuffleItems.Subscribe(_ =>
@@ -29,7 +29,7 @@ namespace BindingTest.ViewModels
         }
 
         public ObservableCollection<TestItem> Items { get; }
-        public ObservableCollection<int> SelectedItems { get; }
+        public ObservableCollection<TestItem> SelectedItems { get; }
         public ReactiveCommand<object> ShuffleItems { get; }
 
         public string BooleanString

src/Perspex.Controls/ListBox.cs

@@ -1,6 +1,7 @@
 // Copyright (c) The Perspex Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using System.Collections;
 using System.Collections.Generic;
 using Perspex.Collections;
 using Perspex.Controls.Generators;
@@ -17,7 +18,7 @@ namespace Perspex.Controls
         /// <summary>
         /// Defines the <see cref="SelectedItems"/> property.
         /// </summary>
-        public static readonly new PerspexProperty<IList<object>> SelectedItemsProperty =
+        public static readonly new PerspexProperty<IList> SelectedItemsProperty =
             SelectingItemsControl.SelectedItemsProperty;
 
         /// <summary>
@@ -27,7 +28,7 @@ namespace Perspex.Controls
             SelectingItemsControl.SelectionModeProperty;
 
         /// <inheritdoc/>
-        public new IList<object> SelectedItems
+        public new IList SelectedItems
         {
             get { return base.SelectedItems; }
         }

src/Perspex.Controls/Primitives/SelectingItemsControl.cs

@@ -57,8 +57,8 @@ namespace Perspex.Controls.Primitives
         /// <summary>
         /// Defines the <see cref="SelectedItems"/> property.
         /// </summary>
-        protected static readonly PerspexProperty<IList<object>> SelectedItemsProperty =
-            PerspexProperty.RegisterDirect<SelectingItemsControl, IList<object>>(
+        protected static readonly PerspexProperty<IList> SelectedItemsProperty =
+            PerspexProperty.RegisterDirect<SelectingItemsControl, IList>(
                 nameof(SelectedItems),
                 o => o.SelectedItems,
                 (o, v) => o.SelectedItems = v);
@@ -80,7 +80,7 @@ namespace Perspex.Controls.Primitives
 
         private int _selectedIndex = -1;
         private object _selectedItem;
-        private IList<object> _selectedItems;
+        private IList _selectedItems;
         private bool _ignoreContainerSelectionChanged;
 
         /// <summary>
@@ -153,7 +153,7 @@ namespace Perspex.Controls.Primitives
                             SelectedItems.Add(effective);
                         }
                     }
-                    else
+                    else if (SelectedItems.Count > 0)
                     {
                         SelectedItems.Clear();
                     }
@@ -164,7 +164,7 @@ namespace Perspex.Controls.Primitives
         /// <summary>
         /// Gets the selected items.
         /// </summary>
-        protected IList<object> SelectedItems
+        protected IList SelectedItems
         {
             get
             {
@@ -470,7 +470,7 @@ namespace Perspex.Controls.Primitives
         /// </summary>
         /// <param name="items">The items collection.</param>
         /// <param name="desired">The desired items.</param>
-        private static void SynchronizeItems(IList<object> items, IEnumerable<object> desired)
+        private static void SynchronizeItems(IList items, IEnumerable<object> desired)
         {
             int index = 0;
 
@@ -692,7 +692,7 @@ namespace Perspex.Controls.Primitives
         /// Called when items are added to the <see cref="SelectedItems"/> collection.
         /// </summary>
         /// <param name="items">The added items.</param>
-        private void SelectedItemsAdded(IList<object> items)
+        private void SelectedItemsAdded(IList items)
         {
             if (items.Count > 0)
             {

tests/Perspex.Controls.UnitTests/Primitives/SelectingItemsControlTests_Multiple.cs

@@ -1,6 +1,7 @@
 // Copyright (c) The Perspex Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 using Perspex.Collections;
@@ -25,7 +26,7 @@ namespace Perspex.Controls.UnitTests.Primitives
             target.ApplyTemplate();
             target.SelectedIndex = 1;
 
-            Assert.Equal(new[] { "bar" }, target.SelectedItems.ToList());
+            Assert.Equal(new[] { "bar" }, target.SelectedItems.Cast<object>().ToList());
         }
 
         [Fact]
@@ -299,7 +300,7 @@ namespace Perspex.Controls.UnitTests.Primitives
             target.SelectedIndex = 1;
             target.SelectRange(3);
 
-            Assert.Equal(new[] { "bar", "baz", "qux" }, target.SelectedItems.ToList());
+            Assert.Equal(new[] { "bar", "baz", "qux" }, target.SelectedItems.Cast<object>().ToList());
         }
 
         [Fact]
@@ -324,7 +325,7 @@ namespace Perspex.Controls.UnitTests.Primitives
             target.SelectedIndex = 3;
             target.SelectRange(1);
 
-            Assert.Equal(new[] { "qux", "baz", "bar" }, target.SelectedItems.ToList());
+            Assert.Equal(new[] { "qux", "baz", "bar" }, target.SelectedItems.Cast<object>().ToList());
         }
 
         [Fact]
@@ -350,12 +351,12 @@ namespace Perspex.Controls.UnitTests.Primitives
             target.SelectRange(5);
             target.SelectRange(4);
 
-            Assert.Equal(new[] { "baz", "qux", "qiz" }, target.SelectedItems.ToList());
+            Assert.Equal(new[] { "baz", "qux", "qiz" }, target.SelectedItems.Cast<object>().ToList());
         }
 
         private class TestSelector : SelectingItemsControl
         {
-            public new IList<object> SelectedItems
+            public new IList SelectedItems
             {
                 get { return base.SelectedItems; }
                 set { base.SelectedItems = value; }