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

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Linq;
using System.Reactive.Disposables;
using System.Threading.Tasks;
using Avalonia.Collections;
using Avalonia.Controls.Presenters;
using Avalonia.Controls.Primitives;
using Avalonia.Controls.Selection;
using Avalonia.Controls.Templates;
using Avalonia.Data;
using Avalonia.Input;
using Avalonia.Input.Platform;
using Avalonia.Interactivity;
using Avalonia.Layout;
using Avalonia.Markup.Data;
using Avalonia.Platform;
using Avalonia.Styling;
using Avalonia.Threading;
using Avalonia.UnitTests;
using Avalonia.VisualTree;
using Moq;
using Xunit;

namespace Avalonia.Controls.UnitTests.Primitives
{
    public partial class SelectingItemsControlTests
    {
        private MouseTestHelper _helper = new MouseTestHelper();

        [Fact]
        public void SelectedIndex_Should_Initially_Be_Minus_1()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            Assert.Equal(-1, target.SelectedIndex);
        }

        [Fact]
        public void Item_IsSelected_Should_Initially_Be_False()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            Prepare(target);

            Assert.False(items[0].IsSelected);
            Assert.False(items[1].IsSelected);
        }

        [Fact]
        public void Setting_SelectedItem_Should_Set_Item_IsSelected_True()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            Prepare(target);

            target.SelectedItem = items[1];

            Assert.False(items[0].IsSelected);
            Assert.True(items[1].IsSelected);
        }

        [Fact]
        public void Setting_SelectedItem_Before_ApplyTemplate_Should_Set_Item_IsSelected_True()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            target.SelectedItem = items[1];
            Prepare(target);

            Assert.False(items[0].IsSelected);
            Assert.True(items[1].IsSelected);
        }

        [Fact]
        public void SelectedIndex_Should_Be_Minus_1_After_Initialize()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new ListBox();
            target.BeginInit();
            target.Items = items;
            target.Template = Template();
            target.EndInit();

            Assert.Equal(-1, target.SelectedIndex);
        }

        [Fact]
        public void SelectedIndex_Should_Be_Minus_1_Without_Initialize()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new ListBox();
            target.Items = items;
            target.Template = Template();
            target.DataContext = new object();

            Assert.Equal(-1, target.SelectedIndex);
        }

        [Fact]
        public void SelectedIndex_Should_Be_0_After_Initialize_With_AlwaysSelected()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new ListBox();
            target.BeginInit();
            target.SelectionMode = SelectionMode.Single | SelectionMode.AlwaysSelected;
            target.Items = items;
            target.Template = Template();
            target.EndInit();

            Prepare(target);

            Assert.Equal(0, target.SelectedIndex);
        }

        [Fact]
        public void Setting_SelectedIndex_During_Initialize_Should_Select_Item_When_AlwaysSelected_Is_Used()
        {
            var listBox = new ListBox
            {
                SelectionMode = SelectionMode.Single | SelectionMode.AlwaysSelected
            };

            listBox.BeginInit();

            listBox.SelectedIndex = 1;
            var items = new AvaloniaList<string>();
            listBox.Items = items;
            items.Add("A");
            items.Add("B");
            items.Add("C");

            listBox.EndInit();

            Prepare(listBox);

            Assert.Equal("B", listBox.SelectedItem);
        }

        [Fact]
        public void Setting_SelectedIndex_Before_Initialize_Should_Retain_Selection()
        {
            var listBox = new ListBox
            {
                SelectionMode = SelectionMode.Single,
                Items = new[] { "foo", "bar", "baz" },
                SelectedIndex = 1
            };

            listBox.BeginInit();

            listBox.EndInit();

            Assert.Equal(1, listBox.SelectedIndex);
            Assert.Equal("bar", listBox.SelectedItem);
        }

        [Fact]
        public void Setting_SelectedIndex_During_Initialize_Should_Take_Priority_Over_Previous_Value()
        {
            var listBox = new ListBox
            {
                SelectionMode = SelectionMode.Single,
                Items = new[] { "foo", "bar", "baz" },
                SelectedIndex = 2
            };

            listBox.BeginInit();

            listBox.SelectedIndex = 1;

            listBox.EndInit();

            Assert.Equal(1, listBox.SelectedIndex);
            Assert.Equal("bar", listBox.SelectedItem);
        }

        [Fact]
        public void Setting_SelectedItem_Before_Initialize_Should_Retain_Selection()
        {
            var listBox = new ListBox
            {
                SelectionMode = SelectionMode.Single,
                Items = new[] { "foo", "bar", "baz" },
                SelectedItem = "bar"
            };

            listBox.BeginInit();

            listBox.EndInit();

            Assert.Equal(1, listBox.SelectedIndex);
            Assert.Equal("bar", listBox.SelectedItem);
        }


        [Fact]
        public void Setting_SelectedItems_Before_Initialize_Should_Retain_Selection()
        {
            var listBox = new ListBox
            {
                SelectionMode = SelectionMode.Multiple,
                Items = new[] { "foo", "bar", "baz" },
            };

            var selected = new[] { "foo", "bar" };

            foreach (var v in selected)
            {
                listBox.SelectedItems.Add(v);
            }

            listBox.BeginInit();

            listBox.EndInit();

            Assert.Equal(selected, listBox.SelectedItems);
        }

        [Fact]
        public void Setting_SelectedItems_During_Initialize_Should_Take_Priority_Over_Previous_Value()
        {
            var listBox = new ListBox
            {
                SelectionMode = SelectionMode.Multiple,
                Items = new[] { "foo", "bar", "baz" },
            };

            var selected = new[] { "foo", "bar" };

            foreach (var v in new[] { "bar", "baz" })
            {
                listBox.SelectedItems.Add(v);
            }

            listBox.BeginInit();

            listBox.SelectedItems = new AvaloniaList<object>(selected);

            listBox.EndInit();

            Assert.Equal(selected, listBox.SelectedItems);
        }

        [Fact]
        public void Setting_SelectedIndex_Before_Initialize_With_AlwaysSelected_Should_Retain_Selection()
        {
            var listBox = new ListBox
            {
                SelectionMode = SelectionMode.Single | SelectionMode.AlwaysSelected,

                Items = new[] { "foo", "bar", "baz" },
                SelectedIndex = 1
            };

            listBox.BeginInit();

            listBox.EndInit();

            Assert.Equal(1, listBox.SelectedIndex);
            Assert.Equal("bar", listBox.SelectedItem);
        }

        [Fact]
        public void Setting_SelectedIndex_Before_ApplyTemplate_Should_Set_Item_IsSelected_True()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            target.SelectedIndex = 1;
            Prepare(target);

            Assert.False(items[0].IsSelected);
            Assert.True(items[1].IsSelected);
        }

        [Fact]
        public void Setting_SelectedItem_Should_Set_SelectedIndex()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            target.ApplyTemplate();
            target.SelectedItem = items[1];

            Assert.Equal(items[1], target.SelectedItem);
            Assert.Equal(1, target.SelectedIndex);
        }

        [Fact]
        public void SelectedIndex_Item_Is_Updated_As_Items_Removed_When_Last_Item_Is_Selected()
        {
            var items = new ObservableCollection<string>
            {
               "Foo",
               "Bar",
               "FooBar"
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            target.ApplyTemplate();
            target.SelectedItem = items[2];

            Assert.Equal(items[2], target.SelectedItem);
            Assert.Equal(2, target.SelectedIndex);

            items.RemoveAt(0);

            Assert.Equal(items[1], target.SelectedItem);
            Assert.Equal(1, target.SelectedIndex);
        }

        [Fact]
        public void Setting_SelectedItem_To_Not_Present_Item_Should_Clear_Selection()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            target.ApplyTemplate();
            target.SelectedItem = items[1];

            Assert.Equal(items[1], target.SelectedItem);
            Assert.Equal(1, target.SelectedIndex);

            target.SelectedItem = new Item();

            Assert.Null(target.SelectedItem);
            Assert.Equal(-1, target.SelectedIndex);
        }

        [Fact]
        public void Setting_SelectedIndex_Should_Set_SelectedItem()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            target.ApplyTemplate();
            target.SelectedIndex = 1;

            Assert.Equal(items[1], target.SelectedItem);
        }

        [Fact]
        public void Setting_SelectedIndex_Out_Of_Bounds_Should_Clear_Selection()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            target.ApplyTemplate();
            target.SelectedIndex = 2;

            Assert.Equal(-1, target.SelectedIndex);
        }

        [Fact]
        public void Setting_SelectedItem_To_Non_Existent_Item_Should_Clear_Selection()
        {
            var target = new SelectingItemsControl
            {
                Template = Template(),
            };

            target.ApplyTemplate();
            target.SelectedItem = new Item();

            Assert.Equal(-1, target.SelectedIndex);
            Assert.Null(target.SelectedItem);
        }

        [Fact]
        public void Adding_Selected_Item_Should_Update_Selection()
        {
            var items = new AvaloniaList<Item>(new[]
            {
                new Item(),
                new Item(),
            });

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            Prepare(target);
            items.Add(new Item { IsSelected = true });

            Assert.Equal(2, target.SelectedIndex);
            Assert.Equal(items[2], target.SelectedItem);
        }

        [Fact]
        public void Setting_Items_To_Null_Should_Clear_Selection()
        {
            var items = new AvaloniaList<Item>
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            target.ApplyTemplate();
            target.SelectedIndex = 1;

            Assert.Equal(items[1], target.SelectedItem);
            Assert.Equal(1, target.SelectedIndex);

            target.Items = null;

            Assert.Null(target.SelectedItem);
            Assert.Equal(-1, target.SelectedIndex);
        }

        [Fact]
        public void Removing_Selected_Item_Should_Clear_Selection()
        {
            var items = new AvaloniaList<Item>
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            Prepare(target);
            target.SelectedIndex = 1;

            Assert.Equal(items[1], target.SelectedItem);
            Assert.Equal(1, target.SelectedIndex);

            SelectionChangedEventArgs receivedArgs = null;

            target.SelectionChanged += (_, args) => receivedArgs = args;

            var removed = items[1];

            items.RemoveAt(1);

            Assert.Null(target.SelectedItem);
            Assert.Equal(-1, target.SelectedIndex);
            Assert.NotNull(receivedArgs);
            Assert.Empty(receivedArgs.AddedItems);
            Assert.Equal(new[] { removed }, receivedArgs.RemovedItems);
            Assert.False(items.Single().IsSelected);
        }

        [Fact]
        public void Removing_Selected_Item_Should_Update_Selection_With_AlwaysSelected()
        {
            var item0 = new Item();
            var item1 = new Item();
            var items = new AvaloniaList<Item>
            {
                item0,
                item1,
            };

            var target = new TestSelector
            {
                Items = items,
                Template = Template(),
                SelectionMode = SelectionMode.AlwaysSelected,
            };

            Prepare(target);
            target.SelectedIndex = 1;

            Assert.Equal(items[1], target.SelectedItem);
            Assert.Equal(1, target.SelectedIndex);

            SelectionChangedEventArgs receivedArgs = null;

            target.SelectionChanged += (_, args) => receivedArgs = args;

            items.RemoveAt(1);

            Assert.Same(item0, target.SelectedItem);
            Assert.Equal(0, target.SelectedIndex);
            Assert.NotNull(receivedArgs);
            Assert.Equal(new[] { item0 }, receivedArgs.AddedItems);
            Assert.Equal(new[] { item1 }, receivedArgs.RemovedItems);
            Assert.True(items.Single().IsSelected);
        }

        [Fact]
        public void Removing_Selected_Item_Should_Clear_Selection_With_BeginInit()
        {
            var items = new AvaloniaList<Item>
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl();
            target.BeginInit();
            target.Items = items;
            target.Template = Template();
            target.EndInit();

            Prepare(target);
            target.SelectedIndex = 0;

            Assert.Equal(items[0], target.SelectedItem);
            Assert.Equal(0, target.SelectedIndex);

            SelectionChangedEventArgs receivedArgs = null;

            target.SelectionChanged += (_, args) => receivedArgs = args;

            var removed = items[0];

            items.RemoveAt(0);

            Assert.Null(target.SelectedItem);
            Assert.Equal(-1, target.SelectedIndex);
            Assert.NotNull(receivedArgs);
            Assert.Empty(receivedArgs.AddedItems);
            Assert.Equal(new[] { removed }, receivedArgs.RemovedItems);
            Assert.False(items.Single().IsSelected);
        }

        [Fact]
        public void Replacing_Selected_Item_Should_Clear_Selection()
        {
            var items = new AvaloniaList<Item>
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            Prepare(target);
            target.SelectedIndex = 1;

            Assert.Equal(items[1], target.SelectedItem);
            Assert.Equal(1, target.SelectedIndex);

            SelectionChangedEventArgs receivedArgs = null;

            target.SelectionChanged += (_, args) => receivedArgs = args;

            var removed = items[1];
            items[1] = new Item();

            Assert.Null(target.SelectedItem);
            Assert.Equal(-1, target.SelectedIndex);
            Assert.NotNull(receivedArgs);
            Assert.Empty(receivedArgs.AddedItems);
            Assert.Equal(new[] { removed }, receivedArgs.RemovedItems);
            Assert.All(items, x => Assert.False(x.IsSelected));
        }

        [Fact]
        public void Moving_Selected_Item_Should_Clear_Selection()
        {
            var items = new AvaloniaList<Item>
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            Prepare(target);
            target.SelectedIndex = 1;

            Assert.Equal(items[1], target.SelectedItem);
            Assert.Equal(1, target.SelectedIndex);

            SelectionChangedEventArgs receivedArgs = null;

            target.SelectionChanged += (_, args) => receivedArgs = args;

            var removed = items[1];
            items.Move(1, 0);

            Assert.Null(target.SelectedItem);
            Assert.Equal(-1, target.SelectedIndex);
            Assert.NotNull(receivedArgs);
            Assert.Empty(receivedArgs.AddedItems);
            Assert.Equal(new[] { removed }, receivedArgs.RemovedItems);
            Assert.All(items, x => Assert.False(x.IsSelected));
        }

        [Fact]
        public void Resetting_Items_Collection_Should_Clear_Selection()
        {
            // Need to use ObservableCollection here as AvaloniaList signals a Clear as an
            // add + remove.
            var items = new ObservableCollection<Item>
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            target.ApplyTemplate();
            target.SelectedIndex = 1;

            Assert.Equal(items[1], target.SelectedItem);
            Assert.Equal(1, target.SelectedIndex);

            items.Clear();

            Assert.Null(target.SelectedItem);
            Assert.Equal(-1, target.SelectedIndex);
        }

        [Fact]
        public void Raising_IsSelectedChanged_On_Item_Should_Update_Selection()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            Prepare(target);
            target.SelectedItem = items[1];

            Assert.False(items[0].IsSelected);
            Assert.True(items[1].IsSelected);

            items[0].IsSelected = true;
            items[0].RaiseEvent(new RoutedEventArgs(SelectingItemsControl.IsSelectedChangedEvent));

            Assert.Equal(0, target.SelectedIndex);
            Assert.Equal(items[0], target.SelectedItem);
            Assert.True(items[0].IsSelected);
            Assert.False(items[1].IsSelected);
        }

        [Fact]
        public void Clearing_IsSelected_And_Raising_IsSelectedChanged_On_Item_Should_Update_Selection()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            Prepare(target);
            target.SelectedItem = items[1];

            Assert.False(items[0].IsSelected);
            Assert.True(items[1].IsSelected);

            items[1].IsSelected = false;
            items[1].RaiseEvent(new RoutedEventArgs(SelectingItemsControl.IsSelectedChangedEvent));

            Assert.Equal(-1, target.SelectedIndex);
            Assert.Null(target.SelectedItem);
        }

        [Fact]
        public void Raising_IsSelectedChanged_On_Someone_Elses_Item_Should_Not_Update_Selection()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            target.ApplyTemplate();
            target.SelectedItem = items[1];

            var notChild = new Item
            {
                IsSelected = true,
            };

            target.RaiseEvent(new RoutedEventArgs
            {
                RoutedEvent = SelectingItemsControl.IsSelectedChangedEvent,
                Source = notChild,
            });

            Assert.Equal(target.SelectedItem, items[1]);
        }

        [Fact]
        public void Setting_SelectedIndex_Should_Raise_SelectionChanged_Event()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            var called = false;

            target.SelectionChanged += (s, e) =>
            {
                Assert.Same(items[1], e.AddedItems.Cast<object>().Single());
                Assert.Empty(e.RemovedItems);
                called = true;
            };

            target.SelectedIndex = 1;

            Assert.True(called);
        }

        [Fact]
        public void Clearing_SelectedIndex_Should_Raise_SelectionChanged_Event()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
                SelectedIndex = 1,
            };

            Prepare(target);

            var called = false;

            target.SelectionChanged += (s, e) =>
            {
                Assert.Same(items[1], e.RemovedItems.Cast<object>().Single());
                Assert.Empty(e.AddedItems);
                called = true;
            };

            target.SelectedIndex = -1;

            Assert.True(called);
        }

        [Fact]
        public void Setting_SelectedIndex_Should_Raise_PropertyChanged_Events()
        {
            var items = new ObservableCollection<string> { "foo", "bar", "baz" };

            var target = new TestSelector
            {
                Items = items,
                Template = Template(),
            };

            var selectedIndexRaised = 0;
            var selectedItemRaised = 0;

            target.PropertyChanged += (s, e) =>
            {
                if (e.Property == SelectingItemsControl.SelectedIndexProperty)
                {
                    Assert.Equal(-1, e.OldValue);
                    Assert.Equal(1, e.NewValue);
                    ++selectedIndexRaised;
                }
                else if (e.Property == SelectingItemsControl.SelectedItemProperty)
                {
                    Assert.Null(e.OldValue);
                    Assert.Equal("bar", e.NewValue);
                    ++selectedItemRaised;
                }
            };

            target.SelectedIndex = 1;

            Assert.Equal(1, selectedIndexRaised);
            Assert.Equal(1, selectedItemRaised);
        }

        [Fact]
        public void Removing_Selected_Item_Should_Raise_PropertyChanged_Events()
        {
            var items = new ObservableCollection<string> { "foo", "bar", "baz" };

            var target = new TestSelector
            {
                Items = items,
                Template = Template(),
            };

            var selectedIndexRaised = 0;
            var selectedItemRaised = 0;
            target.SelectedIndex = 1;

            target.PropertyChanged += (s, e) =>
            {
                if (e.Property == SelectingItemsControl.SelectedIndexProperty)
                {
                    Assert.Equal(1, e.OldValue);
                    Assert.Equal(-1, e.NewValue);
                    ++selectedIndexRaised;
                }
                else if (e.Property == SelectingItemsControl.SelectedItemProperty)
                {
                    Assert.Equal("bar", e.OldValue);
                    Assert.Null(e.NewValue);
                }
            };

            items.RemoveAt(1);

            Assert.Equal(1, selectedIndexRaised);
            Assert.Equal(0, selectedItemRaised);
        }

        [Fact]
        public void Removing_Selected_Item0_Should_Raise_PropertyChanged_Events_With_AlwaysSelected()
        {
            var items = new ObservableCollection<string> { "foo", "bar", "baz" };

            var target = new TestSelector
            {
                Items = items,
                Template = Template(),
                SelectionMode = SelectionMode.AlwaysSelected,
            };

            var selectedIndexRaised = 0;
            var selectedItemRaised = 0;
            target.SelectedIndex = 0;

            target.PropertyChanged += (s, e) =>
            {
                if (e.Property == SelectingItemsControl.SelectedIndexProperty)
                {
                    ++selectedIndexRaised;
                }
                else if (e.Property == SelectingItemsControl.SelectedItemProperty)
                {
                    Assert.Equal("foo", e.OldValue);
                    Assert.Equal("bar", e.NewValue);
                    ++selectedItemRaised;
                }
            };

            items.RemoveAt(0);

            Assert.Equal(0, selectedIndexRaised);
            Assert.Equal(1, selectedItemRaised);
        }

        [Fact]
        public void Removing_Selected_Item1_Should_Raise_PropertyChanged_Events_With_AlwaysSelected()
        {
            var items = new ObservableCollection<string> { "foo", "bar", "baz" };

            var target = new TestSelector
            {
                Items = items,
                Template = Template(),
                SelectionMode = SelectionMode.AlwaysSelected,
            };

            var selectedIndexRaised = 0;
            var selectedItemRaised = 0;
            target.SelectedIndex = 1;

            target.PropertyChanged += (s, e) =>
            {
                if (e.Property == SelectingItemsControl.SelectedIndexProperty)
                {
                    Assert.Equal(1, e.OldValue);
                    Assert.Equal(0, e.NewValue);
                    ++selectedIndexRaised;
                }
                else if (e.Property == SelectingItemsControl.SelectedItemProperty)
                {
                    Assert.Equal("bar", e.OldValue);
                    Assert.Equal("foo", e.NewValue);
                }
            };

            items.RemoveAt(1);

            Assert.Equal(1, selectedIndexRaised);
            Assert.Equal(0, selectedItemRaised);
        }

        [Fact]
        public void Removing_Item_Before_Selection_Should_Raise_PropertyChanged_Events()
        {
            var items = new ObservableCollection<string> { "foo", "bar", "baz" };

            var target = new SelectingItemsControl
            {
                Items = items,
                Template = Template(),
            };

            var selectedIndexRaised = 0;
            var selectedItemRaised = 0;
            target.SelectedIndex = 1;

            target.PropertyChanged += (s, e) =>
            {
                if (e.Property == SelectingItemsControl.SelectedIndexProperty)
                {
                    Assert.Equal(1, e.OldValue);
                    Assert.Equal(0, e.NewValue);
                    ++selectedIndexRaised;
                }
                else if (e.Property == SelectingItemsControl.SelectedItemProperty)
                {
                    ++selectedItemRaised;
                }
            };

            items.RemoveAt(0);

            Assert.Equal(1, selectedIndexRaised);
            Assert.Equal(0, selectedItemRaised);
        }

        [Fact]
        public void Order_Of_Setting_Items_And_SelectedIndex_During_Initialization_Should_Not_Matter()
        {
            using var app = Start();
            var items = new[] { "Foo", "Bar" };
            var target = new SelectingItemsControl();

            ((ISupportInitialize)target).BeginInit();
            target.SelectedIndex = 1;
            target.Items = items;
            ((ISupportInitialize)target).EndInit();

            Prepare(target);

            Assert.Equal(1, target.SelectedIndex);
            Assert.Equal("Bar", target.SelectedItem);
        }

        [Fact]
        public void Order_Of_Setting_Items_And_SelectedItem_During_Initialization_Should_Not_Matter()
        {
            using var app = Start();
            var items = new[] { "Foo", "Bar" };
            var target = new SelectingItemsControl();

            ((ISupportInitialize)target).BeginInit();
            target.SelectedItem = "Bar";
            target.Items = items;
            ((ISupportInitialize)target).EndInit();

            Prepare(target);

            Assert.Equal(1, target.SelectedIndex);
            Assert.Equal("Bar", target.SelectedItem);
        }

        [Fact]
        public void Changing_DataContext_Should_Not_Clear_Nested_ViewModel_SelectedItem()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
            };

            var vm = new MasterViewModel
            {
                Child = new ChildViewModel
                {
                    Items = items,
                    SelectedItem = items[1],
                }
            };

            var target = new SelectingItemsControl { DataContext = vm };
            var itemsBinding = new Binding("Child.Items");
            var selectedBinding = new Binding("Child.SelectedItem");

            target.Bind(SelectingItemsControl.ItemsProperty, itemsBinding);
            target.Bind(SelectingItemsControl.SelectedItemProperty, selectedBinding);

            Assert.Equal(1, target.SelectedIndex);
            Assert.Same(vm.Child.SelectedItem, target.SelectedItem);

            items = new[]
            {
                new Item { Value = "Item1" },
                new Item { Value = "Item2" },
                new Item { Value = "Item3" },
            };

            vm = new MasterViewModel
            {
                Child = new ChildViewModel
                {
                    Items = items,
                    SelectedItem = items[2],
                }
            };

            target.DataContext = vm;

            Assert.Equal(2, target.SelectedIndex);
            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 Control[]
                {
                    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);
        }

        [Fact]
        public void Setting_SelectedItem_With_Pointer_Should_Set_TabOnceActiveElement()
        {
            using (UnitTestApplication.Start())
            {
                var target = new ListBox
                {
                    Template = Template(),
                    Items = new[] { "Foo", "Bar", "Baz " },
                };
                AvaloniaLocator.CurrentMutable.Bind<PlatformHotkeyConfiguration>().ToConstant(new Mock<PlatformHotkeyConfiguration>().Object);
                Prepare(target);
                _helper.Down((Interactive)target.Presenter.Panel.Children[1]);

                var panel = target.Presenter.Panel;

                Assert.Equal(
                    KeyboardNavigation.GetTabOnceActiveElement((InputElement)panel),
                    panel.Children[1]);
            }
        }

        [Fact]
        public void Removing_SelectedItem_Should_Clear_TabOnceActiveElement()
        {
            using (UnitTestApplication.Start())
            {
                var items = new ObservableCollection<string>(new[] { "Foo", "Bar", "Baz " });

                var target = new ListBox
                {
                    Template = Template(),
                    Items = items,
                };
                AvaloniaLocator.CurrentMutable.Bind<PlatformHotkeyConfiguration>().ToConstant(new Mock<PlatformHotkeyConfiguration>().Object);
                Prepare(target);

                _helper.Down(target.Presenter.Panel.Children[1]);

                items.RemoveAt(1);

                var panel = target.Presenter.Panel;

                Assert.Null(KeyboardNavigation.GetTabOnceActiveElement((InputElement)panel));
            }
        }

        [Fact]
        public void Resetting_Items_Collection_Should_Retain_Selection()
        {
            var itemsMock = new Mock<List<string>>();
            var itemsMockAsINCC = itemsMock.As<INotifyCollectionChanged>();

            itemsMock.Object.AddRange(new[] { "Foo", "Bar", "Baz" });
            var target = new SelectingItemsControl
            {
                Items = itemsMock.Object
            };

            target.SelectedIndex = 1;

            itemsMockAsINCC.Raise(e => e.CollectionChanged += null, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));

            Assert.True(target.SelectedIndex == 1);
        }

        [Fact]
        public void Binding_With_DelayedBinding_And_Initialization_Where_DataContext_Is_Root_Works()
        {
            // Test for #1932.
            var root = new RootWithItems();

            root.BeginInit();
            root.DataContext = root;

            var target = new ListBox();
            target.BeginInit();
            root.Child = target;

            DelayedBinding.Add(target, ItemsControl.ItemsProperty, new Binding(nameof(RootWithItems.Items)));
            DelayedBinding.Add(target, ListBox.SelectedItemProperty, new Binding(nameof(RootWithItems.Selected)));
            target.EndInit();
            root.EndInit();

            Assert.Equal("b", target.SelectedItem);
        }

        [Fact]
        public void Mode_For_SelectedIndex_Is_TwoWay_By_Default()
        {
            var items = new[]
            {
                new Item(),
                new Item(),
                new Item(),
            };

            var vm = new MasterViewModel
            {
                Child = new ChildViewModel
                {
                    Items = items,
                    SelectedIndex = 1,
                }
            };

            var target = new SelectingItemsControl { DataContext = vm };
            var itemsBinding = new Binding("Child.Items");
            var selectedIndBinding = new Binding("Child.SelectedIndex");

            target.Bind(SelectingItemsControl.ItemsProperty, itemsBinding);
            target.Bind(SelectingItemsControl.SelectedIndexProperty, selectedIndBinding);

            Assert.Equal(1, target.SelectedIndex);

            target.SelectedIndex = 2;

            Assert.Equal(2, target.SelectedIndex);
            Assert.Equal(2, vm.Child.SelectedIndex);
        }

        [Fact]
        public void Should_Select_Correct_Item_When_Duplicate_Items_Are_Present()
        {
            using (UnitTestApplication.Start())
            {
                var target = new ListBox
                {
                    Template = Template(),
                    Items = new[] { "Foo", "Bar", "Baz", "Foo", "Bar", "Baz" },
                };
                AvaloniaLocator.CurrentMutable.Bind<PlatformHotkeyConfiguration>().ToConstant(new Mock<PlatformHotkeyConfiguration>().Object);
                Prepare(target);
                _helper.Down((Interactive)target.Presenter.Panel.Children[3]);

                Assert.Equal(3, target.SelectedIndex);
            }
        }

        [Fact]
        public void Should_Apply_Selected_Pseudoclass_To_Correct_Item_When_Duplicate_Items_Are_Present()
        {
            using (UnitTestApplication.Start())
            {
                var target = new ListBox
                {
                    Template = Template(),
                    Items = new[] { "Foo", "Bar", "Baz", "Foo", "Bar", "Baz" },
                };
                AvaloniaLocator.CurrentMutable.Bind<PlatformHotkeyConfiguration>().ToConstant(new Mock<PlatformHotkeyConfiguration>().Object);
                Prepare(target);
                _helper.Down((Interactive)target.Presenter.Panel.Children[3]);

                Assert.Equal(new[] { ":pressed", ":selected" }, target.Presenter.Panel.Children[3].Classes);
            }
        }

        [Fact]
        public void Adding_Item_Before_SelectedItem_Should_Update_SelectedIndex()
        {
            var items = new ObservableCollection<string>
            {
               "Foo",
               "Bar",
               "Baz"
            };

            var target = new ListBox
            {
                Template = Template(),
                Items = items,
                SelectedIndex = 1,
            };

            Prepare(target);

            items.Insert(0, "Qux");

            Assert.Equal(2, target.SelectedIndex);
            Assert.Equal("Bar", target.SelectedItem);
        }

        [Fact]
        public void Removing_Item_Before_SelectedItem_Should_Update_SelectedIndex()
        {
            var items = new ObservableCollection<string>
            {
               "Foo",
               "Bar",
               "Baz"
            };

            var target = new ListBox
            {
                Template = Template(),
                Items = items,
                SelectedIndex = 1,
            };

            Prepare(target);

            items.RemoveAt(0);

            Assert.Equal(0, target.SelectedIndex);
            Assert.Equal("Bar", target.SelectedItem);
        }

        [Fact]
        public void Binding_SelectedIndex_Selects_Correct_Item()
        {
            // Issue #4496 (part 2)
            var items = new ObservableCollection<string>();

            var other = new ListBox
            {
                Template = Template(),
                Items = items,
                SelectionMode = SelectionMode.AlwaysSelected,
            };

            var target = new ListBox
            {
                Template = Template(),
                Items = items,
                [!ListBox.SelectedIndexProperty] = other[!ListBox.SelectedIndexProperty],
            };

            Prepare(other);
            Prepare(target);

            items.Add("Foo");

            Assert.Equal(0, other.SelectedIndex);
            Assert.Equal(0, target.SelectedIndex);
        }

        [Fact]
        public void Binding_SelectedItem_Selects_Correct_Item()
        {
            // Issue #4496 (part 2)
            var items = new ObservableCollection<string>();

            var other = new ListBox
            {
                Template = Template(),
                Items = items,
                SelectionMode = SelectionMode.AlwaysSelected,
            };

            var target = new ListBox
            {
                Template = Template(),
                Items = items,
                [!ListBox.SelectedItemProperty] = other[!ListBox.SelectedItemProperty],
            };

            Prepare(target);
            other.ApplyTemplate();
            other.Presenter.ApplyTemplate();

            items.Add("Foo");

            Assert.Equal(0, other.SelectedIndex);
            Assert.Equal(0, target.SelectedIndex);
        }

        [Fact]
        public void Replacing_Selected_Item_Should_Update_SelectedItem()
        {
            var items = new ObservableCollection<string>
            {
               "Foo",
               "Bar",
               "Baz"
            };

            var target = new ListBox
            {
                Template = Template(),
                Items = items,
                SelectedIndex = 1,
            };

            Prepare(target);

            items[1] = "Qux";

            Assert.Equal(-1, target.SelectedIndex);
            Assert.Null(target.SelectedItem);
        }

        [Fact]
        public void AutoScrollToSelectedItem_Causes_Scroll_To_SelectedItem()
        {
            var items = new ObservableCollection<string>
            {
               "Foo",
               "Bar",
               "Baz"
            };

            var target = new ListBox
            {
                Template = Template(),
                Items = items,
            };

            var raised = false;

            Prepare(target);
            target.AddHandler(Control.RequestBringIntoViewEvent, (s, e) => raised = true);
            target.SelectedIndex = 2;

            Assert.True(raised);
        }

        [Fact]
        public void AutoScrollToSelectedItem_Causes_Scroll_To_Initial_SelectedItem()
        {
            var items = new ObservableCollection<string>
            {
               "Foo",
               "Bar",
               "Baz"
            };

            var target = new ListBox
            {
                Template = Template(),
                Items = items,
            };

            var raised = false;

            target.AddHandler(Control.RequestBringIntoViewEvent, (s, e) => raised = true);
            target.SelectedIndex = 2;
            Prepare(target);

            Assert.True(raised);
        }

        [Fact]
        public void AutoScrollToSelectedItem_On_Reset_Works()
        {
            // Issue #3148
            using (UnitTestApplication.Start(TestServices.StyledWindow))
            {
                var items = new ResettingCollection(100);

                var target = new ListBox
                {
                    Items = items,
                    ItemTemplate = new FuncDataTemplate<string>((x, _) =>
                        new TextBlock
                        {
                            Text = x,
                            Width = 100,
                            Height = 10
                        }),
                    AutoScrollToSelectedItem = true,
                };

                var root = new TestRoot(true, target);
                root.Measure(new Size(100, 100));
                root.Arrange(new Rect(0, 0, 100, 100));

                Assert.True(target.Presenter.Panel.Children.Count > 0);
                Assert.True(target.Presenter.Panel.Children.Count < 100);

                target.SelectedItem = "Item99";

                // #3148 triggered here.
                items.Reset(new[] { "Item99" });
                Layout(target);

                Assert.Equal(0, target.SelectedIndex);
                Assert.Equal(1, target.Presenter.Panel.Children.Where(x => x.IsVisible).Count());
            }
        }

        [Fact]
        public void AutoScrollToSelectedItem_Scrolls_When_Reattached_To_Visual_Tree_If_Selection_Changed_While_Detached_From_Visual_Tree()
        {
            var items = new ObservableCollection<string>
            {
               "Foo",
               "Bar",
               "Baz"
            };

            var target = new ListBox
            {
                Template = Template(),
                Items = items,
                SelectedIndex = 2,
            };

            var raised = false;

            Prepare(target);

            var root = (TestRoot)target.Parent;

            target.AddHandler(Control.RequestBringIntoViewEvent, (s, e) => raised = true);

            root.Child = null;
            target.SelectedIndex = 1;
            root.Child = target;

            Assert.True(raised);
        }

        [Fact]
        public void AutoScrollToSelectedItem_Doesnt_Scroll_If_Reattached_To_Visual_Tree_With_No_Selection_Change()
        {
            var items = new ObservableCollection<string>
            {
               "Foo",
               "Bar",
               "Baz"
            };

            var target = new ListBox
            {
                Template = Template(),
                Items = items,
                SelectedIndex = 2,
            };

            var raised = false;

            Prepare(target);

            var root = (TestRoot)target.Parent;

            target.AddHandler(Control.RequestBringIntoViewEvent, (s, e) => raised = true);

            root.Child = null;
            root.Child = target;

            Assert.False(raised);
        }

        [Fact]
        public void AutoScrollToSelectedItem_Causes_Scroll_When_Turned_On()
        {
            var items = new ObservableCollection<string>
            {
               "Foo",
               "Bar",
               "Baz"
            };

            var target = new ListBox
            {
                Template = Template(),
                Items = items,
                AutoScrollToSelectedItem = false,
            };

            Prepare(target);

            var raised = false;
            target.AddHandler(Control.RequestBringIntoViewEvent, (s, e) => raised = true);
            target.SelectedIndex = 2;

            Assert.False(raised);

            target.AutoScrollToSelectedItem = true;

            Assert.True(raised);
        }

        [Fact]
        public void Can_Set_Both_SelectedItem_And_SelectedItems_During_Initialization()
        {
            // Issue #2969.
            var target = new ListBox();
            var selectedItems = new List<object>();

            target.BeginInit();
            target.Template = Template();
            target.Items = new[] { "Foo", "Bar", "Baz" };
            target.SelectedItems = selectedItems;
            target.SelectedItem = "Bar";
            target.EndInit();

            Prepare(target);

            Assert.Equal("Bar", target.SelectedItem);
            Assert.Equal(1, target.SelectedIndex);
            Assert.Same(selectedItems, target.SelectedItems);
            Assert.Equal(new[] { "Bar" }, selectedItems);
        }

        [Fact(Timeout = 2000)]
        public async Task MoveSelection_Wrap_Does_Not_Hang_With_No_Focusable_Controls()
        {
            // Issue #3094.
            var target = new TestSelector
            {
                Template = Template(),
                Items = new[]
                {
                    new ListBoxItem { Focusable = false },
                    new ListBoxItem { Focusable = false },
                },
                SelectedIndex = 0,
            };

            target.Measure(new Size(100, 100));
            target.Arrange(new Rect(0, 0, 100, 100));

            // Timeout in xUnit doesn't work with synchronous methods so we need to apply hack below.
            // https://github.com/xunit/xunit/issues/2222
            await Task.Run(() => target.MoveSelection(NavigationDirection.Next, true));
        }

        [Fact]
        public void MoveSelection_Skips_Non_Focusable_Controls_When_Moving_To_Last_Item()
        {
            var target = new TestSelector
            {
                Template = Template(),
                Items = new[]
                {
                    new ListBoxItem(),
                    new ListBoxItem { Focusable = false },
                }
            };

            target.Measure(new Size(100, 100));
            target.Arrange(new Rect(0, 0, 100, 100));
            target.MoveSelection(NavigationDirection.Last, true);

            Assert.Equal(0, target.SelectedIndex);
        }

        [Fact]
        public void MoveSelection_Skips_Non_Focusable_Controls_When_Moving_To_First_Item()
        {
            var target = new TestSelector
            {
                Template = Template(),
                Items = new[]
                {
                    new ListBoxItem { Focusable = false },
                    new ListBoxItem(),
                }
            };

            target.Measure(new Size(100, 100));
            target.Arrange(new Rect(0, 0, 100, 100));
            target.MoveSelection(NavigationDirection.Last, true);

            Assert.Equal(1, target.SelectedIndex);
        }

        [Fact(Timeout = 2000)]
        public async Task MoveSelection_Does_Not_Hang_When_All_Items_Are_Non_Focusable_And_We_Move_To_First_Item()
        {
            var target = new TestSelector
            {
                Template = Template(),
                Items = new[]
                {
                    new ListBoxItem { Focusable = false },
                    new ListBoxItem { Focusable = false },
                }
            };

            target.Measure(new Size(100, 100));
            target.Arrange(new Rect(0, 0, 100, 100));

            // Timeout in xUnit doesn't work with synchronous methods so we need to apply hack below.
            // https://github.com/xunit/xunit/issues/2222
            await Task.Run(() => target.MoveSelection(NavigationDirection.First, true));

            Assert.Equal(-1, target.SelectedIndex);
        }

        [Fact(Timeout = 2000)]
        public async Task MoveSelection_Does_Not_Hang_When_All_Items_Are_Non_Focusable_And_We_Move_To_Last_Item()
        {
            var target = new TestSelector
            {
                Template = Template(),
                Items = new[]
                {
                    new ListBoxItem { Focusable = false },
                    new ListBoxItem { Focusable = false },
                }
            };

            target.Measure(new Size(100, 100));
            target.Arrange(new Rect(0, 0, 100, 100));

            // Timeout in xUnit doesn't work with synchronous methods so we need to apply hack below.
            // https://github.com/xunit/xunit/issues/2222
            await Task.Run(() => target.MoveSelection(NavigationDirection.Last, true));

            Assert.Equal(-1, target.SelectedIndex);
        }

        [Fact]
        public void MoveSelection_Does_Select_Disabled_Controls()
        {
            // Issue #3426.
            var target = new TestSelector
            {
                Template = Template(),
                Items = new[]
                {
                    new ListBoxItem(),
                    new ListBoxItem { IsEnabled = false },
                },
                SelectedIndex = 0,
            };

            target.Measure(new Size(100, 100));
            target.Arrange(new Rect(0, 0, 100, 100));
            target.MoveSelection(NavigationDirection.Next, true);

            Assert.Equal(0, target.SelectedIndex);
        }

        [Fact]
        public void Pre_Selecting_Item_Should_Set_Selection_After_It_Was_Added_When_AlwaysSelected()
        {
            var target = new TestSelector(SelectionMode.AlwaysSelected)
            {
                Template = Template()
            };

            var second = new Item { IsSelected = true };

            var items = new AvaloniaList<object>
            {
                new Item(),
                second
            };

            target.Items = items;

            Prepare(target);

            Assert.Equal(second, target.SelectedItem);

            Assert.Equal(1, target.SelectedIndex);
        }

        [Fact]
        public void Setting_SelectionMode_Should_Update_SelectionModel()
        {
            var target = new TestSelector();
            var model = target.Selection;

            Assert.True(model.SingleSelect);

            target.SelectionMode = SelectionMode.Multiple;

            Assert.False(model.SingleSelect);
        }

        [Fact]
        public void Does_The_Best_It_Can_With_AutoSelecting_ViewModel()
        {
            // Tests the following scenario:
            //
            // - Items changes from empty to having 1 item
            // - ViewModel auto-selects item 0 in CollectionChanged
            // - SelectionModel receives CollectionChanged
            // - And so adjusts the selected item from 0 to 1, which is past the end of the items.
            //
            // There's not much we can do about this situation because the order in which
            // CollectionChanged handlers are called can't be known (the problem also exists with
            // WPF). The best we can do is not select an invalid index.
            var vm = new SelectionViewModel();

            vm.Items.CollectionChanged += (s, e) =>
            {
                if (vm.SelectedIndex == -1 && vm.Items.Count > 0)
                {
                    vm.SelectedIndex = 0;
                }
            };

            var target = new ListBox
            {
                [!ListBox.ItemsProperty] = new Binding("Items"),
                [!ListBox.SelectedIndexProperty] = new Binding("SelectedIndex"),
                DataContext = vm,
            };

            Prepare(target);

            vm.Items.Add("foo");
            vm.Items.Add("bar");

            Assert.Equal(0, target.SelectedIndex);
            Assert.Equal(new[] { 0 }, target.Selection.SelectedIndexes);
            Assert.Equal("foo", target.SelectedItem);
            Assert.Equal(new[] { "foo" }, target.SelectedItems);
        }

        [Fact]
        public void Preserves_Initial_SelectedItems_When_Bound()
        {
            // Issue #4272 (there are two issues there, this addresses the second one).
            var vm = new SelectionViewModel
            {
                Items = { "foo", "bar", "baz" },
                SelectedItems = { "bar" },
            };

            var target = new ListBox
            {
                [!ListBox.ItemsProperty] = new Binding("Items"),
                [!ListBox.SelectedItemsProperty] = new Binding("SelectedItems"),
                DataContext = vm,
            };

            Prepare(target);

            Assert.Equal(1, target.SelectedIndex);
            Assert.Equal(new[] { 1 }, target.Selection.SelectedIndexes);
            Assert.Equal("bar", target.SelectedItem);
            Assert.Equal(new[] { "bar" }, target.SelectedItems);
        }

        [Fact]
        public void Preserves_SelectedItem_When_Items_Changed()
        {
            // Issue #4048
            using var app = Start();
            var target = new SelectingItemsControl
            {
                Items = new[] { "foo", "bar", "baz"},
                SelectedItem = "bar",
            };

            Prepare(target);

            Assert.Equal(1, target.SelectedIndex);
            Assert.Equal("bar", target.SelectedItem);

            target.Items = new[] { "qux", "foo", "bar" };

            Assert.Equal(2, target.SelectedIndex);
            Assert.Equal("bar", target.SelectedItem);
        }

        [Fact]
        public void Setting_SelectedItems_Raises_PropertyChanged()
        {
            using var app = Start();
            var target = new TestSelector
            {
                Items = new[] { "foo", "bar", "baz" },
            };

            var raised = 0;
            var newValue = new AvaloniaList<object>();

            Prepare(target);

            target.PropertyChanged += (s, e) =>
            {
                if (e.Property == ListBox.SelectedItemsProperty)
                {
                    Assert.Null(e.OldValue);
                    Assert.Same(newValue, e.NewValue);
                    ++raised;
                }
            };

            target.SelectedItems = newValue;

            Assert.Equal(1, raised);
        }

        [Fact]
        public void Setting_Selection_Raises_SelectedItems_PropertyChanged()
        {
            using var app = Start();
            var target = new TestSelector
            {
                Items = new[] { "foo", "bar", "baz" },
            };

            var raised = 0;
            var oldValue = target.SelectedItems;

            Prepare(target);

            target.PropertyChanged += (s, e) =>
            {
                if (e.Property == ListBox.SelectedItemsProperty)
                {
                    Assert.Same(oldValue, e.OldValue);
                    Assert.Null(e.NewValue);
                    ++raised;
                }
            };

            target.Selection = new SelectionModel<int>();

            Assert.Equal(1, raised);
        }

        [Fact]
        public void Handles_Removing_Last_Item_In_Two_Controls_With_Bound_SelectedIndex()
        {
            var items = new ObservableCollection<string> { "foo" };

            // Simulates problem with TabStrip and Carousel with bound SelectedIndex.
            var tabStrip = new TestSelector 
            { 
                Items = items, 
                SelectionMode = SelectionMode.AlwaysSelected,
            };

            var carousel = new TestSelector
            {
                Items = items,
                [!Carousel.SelectedIndexProperty] = tabStrip[!TabStrip.SelectedIndexProperty],
            };

            var tabStripRaised = 0;
            var carouselRaised = 0;

            tabStrip.SelectionChanged += (s, e) =>
            {
                Assert.Equal(new[] { "foo" }, e.RemovedItems);
                Assert.Empty(e.AddedItems);
                ++tabStripRaised;
            };

            carousel.SelectionChanged += (s, e) =>
            {
                Assert.Equal(new[] { "foo" }, e.RemovedItems);
                Assert.Empty(e.AddedItems);
                ++carouselRaised;
            };

            items.RemoveAt(0);

            Assert.Equal(1, tabStripRaised);
            Assert.Equal(1, carouselRaised);
        }

        [Fact]
        public void Handles_Removing_Last_Item_In_Controls_With_Bound_SelectedItem()
        {
            var items = new ObservableCollection<string> { "foo" };

            // Simulates problem with TabStrip and Carousel with bound SelectedItem.
            var tabStrip = new TestSelector
            {
                Items = items,
                SelectionMode = SelectionMode.AlwaysSelected,
            };

            var carousel = new TestSelector
            {
                Items = items,
                [!Carousel.SelectedItemProperty] = tabStrip[!TabStrip.SelectedItemProperty],
            };

            var tabStripRaised = 0;
            var carouselRaised = 0;

            tabStrip.SelectionChanged += (s, e) =>
            {
                Assert.Equal(new[] { "foo" }, e.RemovedItems);
                Assert.Empty(e.AddedItems);
                ++tabStripRaised;
            };

            carousel.SelectionChanged += (s, e) =>
            {
                Assert.Equal(new[] { "foo" }, e.RemovedItems);
                Assert.Empty(e.AddedItems);
                ++carouselRaised;
            };

            items.RemoveAt(0);

            Assert.Equal(1, tabStripRaised);
            Assert.Equal(1, carouselRaised);
        }

        [Fact]
        public void Setting_IsTextSearchEnabled_Enables_Or_Disables_Text_Search()
        {
            var pti = Mock.Of<IPlatformThreadingInterface>(x => x.CurrentThreadIsLoopThread == true);

            Mock.Get(pti)
                .Setup(v => v.StartTimer(It.IsAny<DispatcherPriority>(), It.IsAny<TimeSpan>(), It.IsAny<Action>()))
                .Returns(Disposable.Empty);

            using (UnitTestApplication.Start(TestServices.StyledWindow.With(threadingInterface: pti)))
            {
                var items = new[]
                {
                    new Item { [TextSearch.TextProperty] = "Foo" }, 
                    new Item { [TextSearch.TextProperty] = "Bar" }
                };

                var target = new SelectingItemsControl
                {
                    Items = items, 
                    Template = Template(), 
                    IsTextSearchEnabled = false
                };

                Prepare(target);

                target.RaiseEvent(new TextInputEventArgs
                {
                    RoutedEvent = InputElement.TextInputEvent,
                    Device = KeyboardDevice.Instance, 
                    Text = "Foo"
                });

                Assert.Null(target.SelectedItem);

                target.IsTextSearchEnabled = true;

                target.RaiseEvent(new TextInputEventArgs
                {
                    RoutedEvent = InputElement.TextInputEvent, 
                    Device = KeyboardDevice.Instance, 
                    Text = "Foo"
                });

                Assert.Equal(items[0], target.SelectedItem);
            }
        }

        private static IDisposable Start()
        {
            return UnitTestApplication.Start(TestServices.StyledWindow);
        }

        private static void Prepare(SelectingItemsControl target)
        {
            var root = new TestRoot
            {
                Child = target,
                Width = 100,
                Height = 100,
                Styles =
                {
                    new Style(x => x.Is<SelectingItemsControl>())
                    {
                        Setters =
                        {
                            new Setter(ListBox.TemplateProperty, Template()),
                        },
                    },
                },
            };

            root.LayoutManager.ExecuteInitialLayoutPass();
        }

        private static void Layout(Control c)
        {
            ((ILayoutRoot)c.GetVisualRoot()).LayoutManager.ExecuteLayoutPass();
        }

        private static FuncControlTemplate Template()
        {
            return new FuncControlTemplate<SelectingItemsControl>((control, scope) =>
                new ItemsPresenter
                {
                    Name = "itemsPresenter",
                    [~ItemsPresenter.ItemsPanelProperty] = control[~ItemsControl.ItemsPanelProperty],
                }.RegisterInNameScope(scope));
        }

        private class Item : Control, ISelectable
        {
            public string Value { get; set; }
            public bool IsSelected { get; set; }
        }

        private class MasterViewModel : NotifyingBase
        {
            private ChildViewModel _child;

            public ChildViewModel Child
            {
                get { return _child; }
                set
                {
                    _child = value;
                    RaisePropertyChanged();
                }
            }
        }

        private class ChildViewModel : NotifyingBase
        {
            public IList<Item> Items { get; set; }
            public Item SelectedItem { get; set; }
            public int SelectedIndex { get; set; }
        }

        private class SelectionViewModel : NotifyingBase
        {
            private int _selectedIndex = -1;

            public SelectionViewModel()
            {
                Items = new ObservableCollection<string>();
                SelectedItems = new ObservableCollection<string>();
            }

            public int SelectedIndex
            {
                get => _selectedIndex;
                set
                {
                    _selectedIndex = value;
                    RaisePropertyChanged();
                }
            }

            public ObservableCollection<string> Items { get; }
            public ObservableCollection<string> SelectedItems { get; }
        }

        private class RootWithItems : TestRoot
        {
            public List<string> Items { get; set; } = new List<string>() { "a", "b", "c", "d", "e" };
            public string Selected { get; set; } = "b";
        }

        private class TestSelector : SelectingItemsControl
        {
            public TestSelector()
            {
                
            }

            public TestSelector(SelectionMode selectionMode)
            {
                SelectionMode = selectionMode;
            }

            public new ISelectionModel Selection
            {
                get => base.Selection;
                set => base.Selection = value;
            }

            public new IList SelectedItems
            {
                get => base.SelectedItems;
                set => base.SelectedItems = value;
            }

            public new SelectionMode SelectionMode
            {
                get => base.SelectionMode;
                set => base.SelectionMode = value;
            }

            public new bool MoveSelection(NavigationDirection direction, bool wrap)
            {
                return base.MoveSelection(direction, wrap);
            }
        }

        private class ResettingCollection : List<string>, INotifyCollectionChanged
        {
            public ResettingCollection(int itemCount)
            {
                AddRange(Enumerable.Range(0, itemCount).Select(x => $"Item{x}"));
            }

            public void Reset(IEnumerable<string> items)
            {
                Clear();
                AddRange(items);
                CollectionChanged?.Invoke(
                    this,
                    new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
            }

            public event NotifyCollectionChangedEventHandler CollectionChanged;
        }
    }
}