Make selecting ranges work.

samples/XamlTestApplicationPcl/Views/MainWindow.paml

@@ -49,7 +49,7 @@
             </TabItem>
             <TabItem Header="Lists">
                 <StackPanel Orientation="Horizontal" VerticalAlignment="Center" HorizontalAlignment="Center">
-                  <ListBox Items="{Binding Items}" SelectionMode="Toggle">
+                  <ListBox Items="{Binding Items}" SelectionMode="Multiple">
                     <ListBox.DataTemplates>
                       <DataTemplate DataType="vm:TestItem">
                         <StackPanel>

src/Perspex.Base/Collections/IPerspexList.cs

@@ -16,6 +16,14 @@ namespace Perspex.Collections
         /// </summary>
         new int Count { get; }
 
+
+        /// <summary>
+        /// Gets or sets the element at the specified index.
+        /// </summary>
+        /// <param name="index">The index.</param>
+        /// <returns>The element at the requested index.</returns>
+        new T this[int index] { get; set; }
+
         /// <summary>
         /// Adds multiple items to the collection.
         /// </summary>

src/Perspex.Base/Collections/PerspexList.cs

@@ -187,17 +187,22 @@ namespace Perspex.Collections
         {
             Contract.Requires<ArgumentNullException>(items != null);
 
-            if (Validate != null)
+            var list = (items as IList) ?? items.ToList();
+
+            if (list.Count > 0)
             {
-                foreach (var item in items)
+                if (Validate != null)
                 {
-                    Validate(item);
+                    foreach (var item in list)
+                    {
+                        Validate((T)item);
+                    }
                 }
-            }
 
-            int index = _inner.Count;
-            _inner.AddRange(items);
-            NotifyAdd((items as IList) ?? items.ToList(), index);
+                int index = _inner.Count;
+                _inner.AddRange(items);
+                NotifyAdd(list, index);
+            }
         }
 
         /// <summary>
@@ -205,9 +210,12 @@ namespace Perspex.Collections
         /// </summary>
         public void Clear()
         {
-            var old = _inner;
-            _inner = new List<T>();
-            NotifyReset(old);
+            if (this.Count > 0)
+            {
+                var old = _inner;
+                _inner = new List<T>();
+                NotifyReset(old);
+            }
         }
 
         /// <summary>
@@ -272,16 +280,21 @@ namespace Perspex.Collections
         {
             Contract.Requires<ArgumentNullException>(items != null);
 
-            if (Validate != null)
+            var list = (items as IList) ?? items.ToList();
+
+            if (list.Count > 0)
             {
-                foreach (var item in items)
+                if (Validate != null)
                 {
-                    Validate(item);
+                    foreach (var item in list)
+                    {
+                        Validate((T)item);
+                    }
                 }
-            }
 
-            _inner.InsertRange(index, items);
-            NotifyAdd((items as IList) ?? items.ToList(), index);
+                _inner.InsertRange(index, items);
+                NotifyAdd((items as IList) ?? items.ToList(), index);
+            }
         }
 
         /// <summary>
@@ -311,7 +324,7 @@ namespace Perspex.Collections
         {
             Contract.Requires<ArgumentNullException>(items != null);
 
-            List<T> removed = new List<T>();
+            var list = (items as IList) ?? items.ToList();
 
             foreach (var i in items)
             {

src/Perspex.Base/Collections/PerspexListExtensions.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Collections.Specialized;
 using System.ComponentModel;
+using System.Linq;
 using System.Reactive.Disposables;
 
 namespace Perspex.Collections
@@ -133,6 +134,66 @@ namespace Perspex.Collections
             return Disposable.Create(() => collection.CollectionChanged -= handler);
         }
 
+        /// <summary>
+        /// Invokes an action for each item in a collection and subsequently each item added or
+        /// removed from the collection.
+        /// </summary>
+        /// <typeparam name="T">The type of the collection items.</typeparam>
+        /// <param name="collection">The collection.</param>
+        /// <param name="added">
+        /// An action called initially with all items in the collection and subsequently with a
+        /// list of items added to the collection. The parameters passed are the index of the
+        /// first item added to the collection and the items added.
+        /// </param>
+        /// <param name="removed">
+        /// An action called with all items removed from the collection. The parameters passed 
+        /// are the index of the first item removed from the collection and the items removed.
+        /// </param>
+        /// <param name="reset">
+        /// An action called when the collection is reset.
+        /// </param>
+        /// <returns>A disposable used to terminate the subscription.</returns>
+        public static IDisposable ForEachItem<T>(
+            this IPerspexReadOnlyList<T> collection,
+            Action<int, IEnumerable<T>> added,
+            Action<int, IEnumerable<T>> removed,
+            Action reset)
+        {
+            NotifyCollectionChangedEventHandler handler = (_, e) =>
+            {
+                switch (e.Action)
+                {
+                    case NotifyCollectionChangedAction.Add:
+                        added(e.NewStartingIndex, e.NewItems.Cast<T>());
+                        break;
+
+                    case NotifyCollectionChangedAction.Replace:
+                        removed(e.OldStartingIndex, e.OldItems.Cast<T>());
+                        added(e.NewStartingIndex, e.NewItems.Cast<T>());
+                        break;
+
+                    case NotifyCollectionChangedAction.Remove:
+                        removed(e.OldStartingIndex, e.OldItems.Cast<T>());
+                        break;
+
+                    case NotifyCollectionChangedAction.Reset:
+                        if (reset == null)
+                        {
+                            throw new InvalidOperationException(
+                                "Reset called on collection without reset handler.");
+                        }
+
+                        reset();
+                        break;
+                }
+            };
+
+            added(0, collection);
+            collection.CollectionChanged += handler;
+
+            return Disposable.Create(() => collection.CollectionChanged -= handler);
+        }
+
         /// <summary>
         /// Listens for property changed events from all items in a collection.
         /// </summary>

src/Perspex.Controls/ListBox.cs

@@ -38,7 +38,7 @@ namespace Perspex.Controls
 
             if (e.NavigationMethod == NavigationMethod.Directional)
             {
-                UpdateSelectionFromEventSource(e.Source, true);
+                UpdateSelectionFromEventSource(e.Source);
             }
         }
 
@@ -49,7 +49,11 @@ namespace Perspex.Controls
 
             if (e.MouseButton == MouseButton.Left || e.MouseButton == MouseButton.Right)
             {
-                UpdateSelectionFromEventSource(e.Source, true);
+                UpdateSelectionFromEventSource(
+                    e.Source,
+                    true,
+                    (e.InputModifiers & InputModifiers.Shift) != 0,
+                    (e.InputModifiers & InputModifiers.Control) != 0);
             }
         }
     }

src/Perspex.Controls/Primitives/SelectingItemsControl.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections;
+using System.Collections.Generic;
 using System.Collections.Specialized;
 using System.Linq;
 using Perspex.Collections;
@@ -103,8 +104,8 @@ namespace Perspex.Controls.Primitives
         {
             ItemContainerGenerator.ContainersInitialized.Subscribe(ContainersInitialized);
             _selectedIndexes.Validate = ValidateIndex;
-            _selectedIndexes.ForEachItem(SelectedIndexAdded, SelectedIndexRemoved, SelectionReset);
-            _selectedItems.ForEachItem(SelectedItemAdded, SelectedItemRemoved, SelectionReset);
+            _selectedIndexes.ForEachItem(SelectedIndexesAdded, SelectedIndexesRemoved, SelectionReset);
+            _selectedItems.ForEachItem(SelectedItemsAdded, SelectedItemsRemoved, SelectionReset);
         }
 
         /// <summary>
@@ -269,20 +270,35 @@ namespace Perspex.Controls.Primitives
         /// </summary>
         /// <param name="index">The index of the item.</param>
         /// <param name="select">Whether the item should be selected or unselected.</param>
-        protected void UpdateSelection(int index, bool select)
+        /// <param name="rangeModifier">Whether the range modifier is enabled (i.e. shift key).</param>
+        /// <param name="toggleModifier">Whether the toggle modifier is enabled (i.e. ctrl key).</param>
+        protected void UpdateSelection(
+            int index,
+            bool select = true,
+            bool rangeModifier = false,
+            bool toggleModifier = false)
         {
             if (index != -1)
             {
                 if (select)
                 {
                     var mode = SelectionMode;
-                    var toggle = (mode & SelectionMode.Toggle) != 0;
+                    var toggle = toggleModifier || (mode & SelectionMode.Toggle) != 0;
                     var multi = (mode & SelectionMode.Multiple) != 0;
+                    var range = multi && SelectedIndexes.Count > 0 ? rangeModifier : false;
 
-                    if (!toggle)
+                    if (!toggle && !range)
                     {
                         SelectedIndex = index;
                     }
+                    else if (multi && range)
+                    {
+                        var first = SelectedIndexes[0];
+
+                        // TODO: Don't deselect items in new selection.
+                        SelectedIndexes.Clear();
+                        SelectedIndexes.AddRange(Range(first, index));
+                    }
                     else
                     {
                         var i = SelectedIndexes.IndexOf(index);
@@ -311,18 +327,36 @@ namespace Perspex.Controls.Primitives
             }
         }
 
+        private IEnumerable<int> Range(int first, int last)
+        {
+            int step = first > last ? -1 : 1;
+
+            for (int i = first; i != last; i += step)
+            {
+                yield return i;
+            }
+
+            yield return last;
+        }
+
         /// <summary>
         /// Updates the selection for a container based on user interaction.
         /// </summary>
         /// <param name="container">The container.</param>
         /// <param name="select">Whether the container should be selected or unselected.</param>
-        protected void UpdateSelection(IControl container, bool select)
+        /// <param name="rangeModifier">Whether the range modifier is enabled (i.e. shift key).</param>
+        /// <param name="toggleModifier">Whether the toggle modifier is enabled (i.e. ctrl key).</param>
+        protected void UpdateSelection(
+            IControl container,
+            bool select = true,
+            bool rangeModifier = false,
+            bool toggleModifier = false)
         {
             var index = ItemContainerGenerator.IndexFromContainer(container);
 
             if (index != -1)
             {
-                UpdateSelection(index, select);
+                UpdateSelection(index, select, rangeModifier, toggleModifier);
             }
         }
 
@@ -332,17 +366,23 @@ namespace Perspex.Controls.Primitives
         /// </summary>
         /// <param name="eventSource">The control that raised the event.</param>
         /// <param name="select">Whether the container should be selected or unselected.</param>
+        /// <param name="rangeModifier">Whether the range modifier is enabled (i.e. shift key).</param>
+        /// <param name="toggleModifier">Whether the toggle modifier is enabled (i.e. ctrl key).</param>
         /// <returns>
         /// True if the event originated from a container that belongs to the control; otherwise
         /// false.
         /// </returns>
-        protected bool UpdateSelectionFromEventSource(IInteractive eventSource, bool select)
+        protected bool UpdateSelectionFromEventSource(
+            IInteractive eventSource, 
+            bool select = true,
+            bool rangeModifier = false,
+            bool toggleModifier = false)
         {
             var item = GetContainerFromEventSource(eventSource);
 
             if (item != null)
             {
-                UpdateSelection(item, select);
+                UpdateSelection(item, select, rangeModifier, toggleModifier);
                 return true;
             }
 
@@ -480,21 +520,27 @@ namespace Perspex.Controls.Primitives
         /// Called when an index is added to the <see cref="SelectedIndexes"/> collection.
         /// </summary>
         /// <param name="listIndex">The index in the SelectedIndexes collection.</param>
-        /// <param name="itemIndex">The item index.</param>
-        private void SelectedIndexAdded(int listIndex, int itemIndex)
+        /// <param name="itemIndexes">The item indexes.</param>
+        private void SelectedIndexesAdded(int listIndex, IEnumerable<int> itemIndexes)
         {
-            if (SelectedIndexes.Count == 1)
+            var indexes = (itemIndexes as IList<int>) ?? itemIndexes.ToList();
+            IControl container = null;
+
+            if (SelectedItems.Count != SelectedIndexes.Count)
             {
-                RaisePropertyChanged(SelectedIndexProperty, -1, itemIndex, BindingPriority.LocalValue);
+                var items = indexes.Select(x => Items.Cast<object>().ElementAt(x));
+                SelectedItems.AddRange(items);
             }
 
-            if (SelectedItems.Count != SelectedIndexes.Count)
+            foreach (var itemIndex in indexes)
             {
-                var item = Items.Cast<object>().ElementAt(itemIndex);
-                SelectedItems.Insert(listIndex, item);
+                container = MarkIndexSelected(itemIndex, true);
             }
 
-            var container = MarkIndexSelected(itemIndex, true);
+            if (SelectedIndexes.Count == 1)
+            {
+                RaisePropertyChanged(SelectedIndexProperty, -1, SelectedIndexes[0], BindingPriority.LocalValue);
+            }
 
             if (container != null && Presenter?.Panel != null)
             {
@@ -506,20 +552,29 @@ namespace Perspex.Controls.Primitives
         /// Called when an index is removed from the <see cref="SelectedIndexes"/> collection.
         /// </summary>
         /// <param name="listIndex">The index in the SelectedIndexes collection.</param>
-        /// <param name="itemIndex">The item index.</param>
-        private void SelectedIndexRemoved(int listIndex, int itemIndex)
+        /// <param name="itemIndexes">The item indexes.</param>
+        private void SelectedIndexesRemoved(int listIndex, IEnumerable<int> itemIndexes)
         {
-            if (SelectedIndexes.Count == 0)
+            var sync = SelectedIndexes.Count != SelectedItems.Count;
+
+            foreach (var itemIndex in itemIndexes)
             {
-                RaisePropertyChanged(SelectedIndexProperty, itemIndex, -1, BindingPriority.LocalValue);
+                if (sync)
+                {
+                    SelectedItems.RemoveAt(listIndex++);
+                }
+
+                MarkIndexSelected(itemIndex, false);
             }
 
-            if (SelectedIndexes.Count != SelectedItems.Count)
+            if (SelectedIndexes.Count == 0)
             {
-                SelectedItems.RemoveAt(listIndex);
+                RaisePropertyChanged(
+                    SelectedIndexProperty, 
+                    itemIndexes.First(), 
+                    -1, 
+                    BindingPriority.LocalValue);
             }
-
-            MarkIndexSelected(itemIndex, false);
         }
 
         /// <summary>
@@ -527,16 +582,16 @@ namespace Perspex.Controls.Primitives
         /// </summary>
         /// <param name="index">The index in the SelectedItems collection.</param>
         /// <param name="item">The item.</param>
-        private void SelectedItemAdded(int index, object item)
+        private void SelectedItemsAdded(int index, object item)
         {
-            if (SelectedItems.Count == 1)
+            if (SelectedIndexes.Count != SelectedItems.Count)
             {
-                RaisePropertyChanged(SelectedItemProperty, null, item, BindingPriority.LocalValue);
+                SelectedIndexes.Insert(index, IndexOf(Items, item));
             }
 
-            if (SelectedIndexes.Count != SelectedItems.Count)
+            if (SelectedItems.Count == 1)
             {
-                SelectedIndexes.Insert(index, IndexOf(Items, item));
+                RaisePropertyChanged(SelectedItemProperty, null, item, BindingPriority.LocalValue);
             }
         }
 
@@ -545,7 +600,7 @@ namespace Perspex.Controls.Primitives
         /// </summary>
         /// <param name="index">The index in the SelectedItems collection.</param>
         /// <param name="item">The item.</param>
-        private void SelectedItemRemoved(int index, object item)
+        private void SelectedItemsRemoved(int index, object item)
         {
             if (SelectedIndexes.Count != SelectedItems.Count)
             {

src/Perspex.Controls/Primitives/TabStrip.cs

@@ -56,7 +56,7 @@ namespace Perspex.Controls.Primitives
 
             if (e.NavigationMethod == NavigationMethod.Directional)
             {
-                UpdateSelectionFromEventSource(e.Source, true);
+                UpdateSelectionFromEventSource(e.Source);
             }
         }
 
@@ -67,7 +67,7 @@ namespace Perspex.Controls.Primitives
 
             if (e.MouseButton == MouseButton.Left)
             {
-                UpdateSelectionFromEventSource(e.Source, true);
+                UpdateSelectionFromEventSource(e.Source);
             }
         }
     }

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

@@ -219,6 +219,58 @@ namespace Perspex.Controls.UnitTests.Primitives
             Assert.False(((ListBoxItem)target.Presenter.Panel.Children[1]).IsSelected);
         }
 
+        [Fact]
+        public void Range_Select_Should_Select_Range()
+        {
+            var target = new TestSelector
+            {
+                Items = new[]
+                {
+                    "foo",
+                    "bar",
+                    "baz",
+                    "qux",
+                    "qiz",
+                    "lol",
+                },
+                SelectionMode = SelectionMode.Multiple,
+                Template = Template(),
+            };
+
+            target.ApplyTemplate();
+            target.SelectedIndex = 1;
+            target.SelectRange(3);
+
+            Assert.Equal(new[] { 1, 2, 3 }, target.SelectedIndexes);
+            Assert.Equal(new[] { "bar", "baz", "qux" }, target.SelectedItems);
+        }
+
+        [Fact]
+        public void Range_Select_Backwards_Should_Select_Range()
+        {
+            var target = new TestSelector
+            {
+                Items = new[]
+                {
+                    "foo",
+                    "bar",
+                    "baz",
+                    "qux",
+                    "qiz",
+                    "lol",
+                },
+                SelectionMode = SelectionMode.Multiple,
+                Template = Template(),
+            };
+
+            target.ApplyTemplate();
+            target.SelectedIndex = 3;
+            target.SelectRange(1);
+
+            Assert.Equal(new[] { 3, 2, 1 }, target.SelectedIndexes);
+            Assert.Equal(new[] { "qux", "baz", "bar" }, target.SelectedItems);
+        }
+
         private class TestSelector : SelectingItemsControl
         {
             public new IPerspexList<int> SelectedIndexes
@@ -230,6 +282,17 @@ namespace Perspex.Controls.UnitTests.Primitives
             {
                 get { return base.SelectedItems; }
             }
+
+            public new SelectionMode SelectionMode
+            {
+                get { return base.SelectionMode; }
+                set { base.SelectionMode = value; }
+            }
+
+            public void SelectRange(int index)
+            {
+                UpdateSelection(index, true, true);
+            }
         }
 
         private ControlTemplate Template()