Prevent nested selection changing parent selection.

Added previously failing
Nested_ListBox_Does_Not_Change_Parent_SelectedIndex test to check it.

src/Perspex.Controls/Presenters/CarouselPresenter.cs

@@ -1,16 +1,12 @@
 // 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;
-using System.Collections;
 using System.Collections.Specialized;
 using System.Linq;
 using System.Reactive.Linq;
 using System.Threading.Tasks;
 using Perspex.Animation;
-using Perspex.Controls.Generators;
 using Perspex.Controls.Primitives;
-using Perspex.Controls.Templates;
 using Perspex.Controls.Utils;
 using Perspex.Data;
 

src/Perspex.Controls/Primitives/SelectingItemsControl.cs

@@ -574,13 +574,22 @@ namespace Perspex.Controls.Primitives
         {
             if (!_ignoreContainerSelectionChanged)
             {
-                var selectable = (ISelectable)e.Source;
+                var control = e.Source as IControl;
+                var selectable = e.Source as ISelectable;
 
-                if (selectable != null)
+                if (control != null &&
+                    selectable != null &&
+                    control.LogicalParent == this &&
+                    ItemContainerGenerator?.IndexFromContainer(control) != -1)
                 {
-                    UpdateSelectionFromEventSource(e.Source, selectable.IsSelected);
+                    UpdateSelection(control, selectable.IsSelected);
                 }
             }
+
+            if (e.Source != this)
+            {
+                e.Handled = true;
+            }
         }
 
         /// <summary>

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

@@ -570,6 +570,41 @@ namespace Perspex.Controls.UnitTests.Primitives
             Assert.Same(vm.Child.SelectedItem, target.SelectedItem);
         }
 
+        [Fact]
+        public void Nested_ListBox_Does_Not_Change_Parent_SelectedIndex()
+        {
+            SelectingItemsControl nested;
+
+            var root = new SelectingItemsControl
+            {
+                Template = Template(),
+                Items = new IControl[]
+                {
+                    new Border(),
+                    nested = new ListBox
+                    {
+                        Template = Template(),
+                        Items = new[] { "foo", "bar" },
+                        SelectedIndex = 1,
+                    }
+                },
+                SelectedIndex = 0,
+            };
+
+            root.ApplyTemplate();
+            root.Presenter.ApplyTemplate();
+            nested.ApplyTemplate();
+            nested.Presenter.ApplyTemplate();
+
+            Assert.Equal(0, root.SelectedIndex);
+            Assert.Equal(1, nested.SelectedIndex);
+
+            nested.SelectedIndex = 0;
+
+            Assert.Equal(0, root.SelectedIndex);
+        }
+
+
         private FuncControlTemplate Template()
         {
             return new FuncControlTemplate<SelectingItemsControl>(control =>