Merge pull request #718 from irihitech/anchor

New Control: Anchor

src/Ursa.Themes.Semi/Controls/Anchor.axaml

@@ -0,0 +1,91 @@
+<ResourceDictionary
+    xmlns="https://github.com/avaloniaui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:converters="clr-namespace:Ursa.Themes.Semi.Converters"
+    xmlns:iri="https://irihi.tech/shared"
+    xmlns:u="https://irihi.tech/ursa">
+    <converters:TreeLevelToPaddingConverter x:Key="LevelToPaddingConverter" />
+    <ControlTheme x:Key="{x:Type u:Anchor}" TargetType="{x:Type u:Anchor}">
+        <Setter Property="Background" Value="Transparent" />
+        <Setter Property="VerticalAlignment" Value="Top" />
+        <Setter Property="Template">
+            <ControlTemplate>
+                <Panel>
+                    <Rectangle
+                        Width="{DynamicResource AnchorPipeWidth}"
+                        Name="PART_Pipe"
+                        HorizontalAlignment="Left"
+                        VerticalAlignment="Stretch"
+                        Fill="{DynamicResource AnchorPipeBackground}" />
+                    <ItemsPresenter
+                        Name="PART_ItemsPresenter"
+                        Margin="{TemplateBinding Padding}"
+                        ItemsPanel="{TemplateBinding ItemsPanel}" />
+                </Panel>
+            </ControlTemplate>
+        </Setter>
+        <Style Selector="^.Muted /template/ Rectangle#PART_Pipe">
+            <Setter Property="Fill" Value="Transparent" />
+        </Style>
+    </ControlTheme>
+
+    <ControlTheme x:Key="{x:Type u:AnchorItem}" TargetType="u:AnchorItem">
+        <Setter Property="Background" Value="Transparent" />
+        <Setter Property="Cursor" Value="Hand" />
+        <Setter Property="iri:ClassHelper.ClassSource" Value="{Binding $parent[u:Anchor]}" />
+        <Setter Property="Template">
+            <ControlTemplate TargetType="u:AnchorItem">
+                <StackPanel>
+                    <Panel Background="{TemplateBinding Background}">
+                        <Border
+                            Name="PART_Pipe"
+                            Width="{DynamicResource AnchorPipeWidth}"
+                            CornerRadius="{DynamicResource AnchorPipeCornerRadius}"
+                            HorizontalAlignment="Left"
+                            VerticalAlignment="Stretch" />
+                        <Panel>
+                            <ContentPresenter
+                                Name="{x:Static iri:PartNames.PART_HeaderPresenter}"
+                                VerticalAlignment="Center"
+                                Foreground="{DynamicResource AnchorForeground}"
+                                Content="{TemplateBinding Header}"
+                                ContentTemplate="{TemplateBinding HeaderTemplate}">
+                                <ContentPresenter.Padding>
+                                    <MultiBinding Converter="{StaticResource LevelToPaddingConverter}">
+                                        <Binding Path="Level" RelativeSource="{RelativeSource AncestorType={x:Type u:AnchorItem}}" />
+                                        <DynamicResource ResourceKey="AnchorIndent" />
+                                    </MultiBinding>
+                                </ContentPresenter.Padding>
+                            </ContentPresenter>
+                        </Panel>
+                    </Panel>
+                    <ItemsPresenter ItemsPanel="{TemplateBinding ItemsPanel}" />
+                </StackPanel>
+            </ControlTemplate>
+        </Setter>
+        <Style Selector="^ /template/ ContentPresenter#PART_HeaderPresenter">
+            <Setter Property="MinHeight" Value="{DynamicResource AnchorDefaultHeight}" />
+        </Style>
+        <Style Selector="^.Small /template/ ContentPresenter#PART_HeaderPresenter">
+            <Setter Property="MinHeight" Value="{DynamicResource AnchorSmallHeight}" />
+            <Setter Property="FontSize" Value="{DynamicResource AnchorSmallFontSize}" />
+        </Style>
+        <Style Selector="^:selected">
+            <Style Selector="^ /template/ ContentPresenter#PART_HeaderPresenter">
+                <Setter Property="Foreground" Value="{DynamicResource AnchorSelectedForeground}" />
+            </Style>
+            <Style Selector="^ /template/ Border#PART_Pipe">
+                <Setter Property="Background" Value="{DynamicResource AnchorPipeSelectedBackground}" />
+            </Style>
+            <Style Selector="^.Primary /template/ Border#PART_Pipe">
+                <Setter Property="Background" Value="{DynamicResource AnchorPipeSelectedPrimaryBackground}" />
+            </Style>
+            <Style Selector="^.Tertiary /template/ Border#PART_Pipe">
+                <Setter Property="Background" Value="{DynamicResource AnchorPipeSelectedTertiaryBackground}" />
+            </Style>
+            <Style Selector="^.Muted /template/ Border#PART_Pipe">
+                <Setter Property="Background" Value="Transparent" />
+            </Style>
+        </Style>
+    </ControlTheme>
+</ResourceDictionary>

src/Ursa.Themes.Semi/Controls/_index.axaml

@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
     <ResourceDictionary.MergedDictionaries>
+        <ResourceInclude Source="Anchor.axaml" />
         <ResourceInclude Source="AutoCompleteBox.axaml" />
         <ResourceInclude Source="Avatar.axaml" />
         <ResourceInclude Source="Badge.axaml" />

src/Ursa.Themes.Semi/Converters/NavigationMenuItemLevelToMarginConverter.cs

@@ -1,23 +0,0 @@
-using System.Globalization;
-using Avalonia;
-using Avalonia.Data.Converters;
-
-namespace Ursa.Themes.Semi.Converters;
-
-public class NavigationMenuItemLevelToMarginConverter: IMultiValueConverter
-{
-    public int Indent { get; set; }
-
-    public object? Convert(IList<object?> values, Type targetType, object? parameter, CultureInfo culture)
-    {
-        if (values[0] is int i && values[1] is bool b)
-        {
-            if (b)
-            {
-                return new Thickness();
-            }
-            return new Thickness((i-1) * Indent, 0, 0, 0);
-        }
-        return new Thickness();
-    }
-}

src/Ursa.Themes.Semi/Converters/TreeLevelToPaddingConverter.cs

@@ -0,0 +1,18 @@
+using System.Globalization;
+using Avalonia;
+using Avalonia.Data.Converters;
+
+namespace Ursa.Themes.Semi.Converters;
+
+public class TreeLevelToPaddingConverter : IMultiValueConverter
+{
+    public object? Convert(IList<object?> values, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if (values[0] is int i && values[1] is Thickness indent)
+        {
+            return new Thickness(Math.Max(i, 0) * indent.Left, indent.Top, indent.Right, indent.Bottom);
+        }
+
+        return new Thickness();
+    }
+}

src/Ursa.Themes.Semi/Themes/Dark/Anchor.axaml

@@ -0,0 +1,8 @@
+<ResourceDictionary xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+    <StaticResource x:Key="AnchorPipeBackground" ResourceKey="SemiColorBorder" />
+    <StaticResource x:Key="AnchorForeground" ResourceKey="SemiColorText2" />
+    <StaticResource x:Key="AnchorSelectedForeground" ResourceKey="SemiColorText0" />
+    <StaticResource x:Key="AnchorPipeSelectedBackground" ResourceKey="SemiColorPrimary" />
+    <StaticResource x:Key="AnchorPipeSelectedPrimaryBackground" ResourceKey="SemiColorPrimary" />
+    <StaticResource x:Key="AnchorPipeSelectedTertiaryBackground" ResourceKey="SemiColorTertiary" />
+</ResourceDictionary>

src/Ursa.Themes.Semi/Themes/Dark/_index.axaml

@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
     <ResourceDictionary.MergedDictionaries>
         <ResourceInclude Source="Avatar.axaml" />
+        <ResourceInclude Source="Anchor.axaml" />
         <ResourceInclude Source="Badge.axaml" />
         <ResourceInclude Source="Banner.axaml" />
         <ResourceInclude Source="Breadcrumb.axaml" />

src/Ursa.Themes.Semi/Themes/HighContrast/Anchor.axaml

@@ -0,0 +1,7 @@
+<ResourceDictionary xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+    <StaticResource x:Key="AnchorPipeBackground" ResourceKey="GrayTextColor" />
+    <StaticResource x:Key="AnchorForeground" ResourceKey="WindowTextColor" />
+    <StaticResource x:Key="AnchorSelectedForeground" ResourceKey="HotlightColor" />
+    <StaticResource x:Key="AnchorPipeSelectedBackground" ResourceKey="HotlightColor" />
+    <StaticResource x:Key="AnchorPipeSelectedPrimaryBackground" ResourceKey="HotlightColor" />
+</ResourceDictionary>

src/Ursa.Themes.Semi/Themes/HighContrast/_index.axaml

@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
     <ResourceDictionary.MergedDictionaries>
+        <ResourceInclude Source="Anchor.axaml" />
         <ResourceInclude Source="Badge.axaml" />
         <ResourceInclude Source="Banner.axaml" />
         <ResourceInclude Source="Breadcrumb.axaml" />

src/Ursa.Themes.Semi/Themes/Light/Anchor.axaml

@@ -0,0 +1,8 @@
+<ResourceDictionary xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+    <StaticResource x:Key="AnchorPipeBackground" ResourceKey="SemiColorBorder" />
+    <StaticResource x:Key="AnchorForeground" ResourceKey="SemiColorText2" />
+    <StaticResource x:Key="AnchorSelectedForeground" ResourceKey="SemiColorText0" />
+    <StaticResource x:Key="AnchorPipeSelectedBackground" ResourceKey="SemiColorPrimary" />
+    <StaticResource x:Key="AnchorPipeSelectedPrimaryBackground" ResourceKey="SemiColorPrimary" />
+    <StaticResource x:Key="AnchorPipeSelectedTertiaryBackground" ResourceKey="SemiColorTertiary" />
+</ResourceDictionary>

src/Ursa.Themes.Semi/Themes/Light/_index.axaml

@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
     <ResourceDictionary.MergedDictionaries>
         <ResourceInclude Source="Avatar.axaml" />
+        <ResourceInclude Source="Anchor.axaml" />
         <ResourceInclude Source="Badge.axaml" />
         <ResourceInclude Source="Banner.axaml" />
         <ResourceInclude Source="Breadcrumb.axaml" />

src/Ursa.Themes.Semi/Themes/Shared/Anchor.axaml

@@ -0,0 +1,8 @@
+<ResourceDictionary xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+    <Thickness x:Key="AnchorIndent">8,4,0,4</Thickness>
+    <x:Double x:Key="AnchorPipeWidth">2</x:Double>
+    <CornerRadius x:Key="AnchorPipeCornerRadius">1</CornerRadius>
+    <x:Double x:Key="AnchorDefaultHeight">20</x:Double>
+    <x:Double x:Key="AnchorSmallHeight">16</x:Double>
+    <x:Double x:Key="AnchorSmallFontSize">12</x:Double>
+</ResourceDictionary>

src/Ursa.Themes.Semi/Themes/Shared/_index.axaml

@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
     <ResourceDictionary.MergedDictionaries>
         <ResourceInclude Source="Avatar.axaml" />
+        <ResourceInclude Source="Anchor.axaml" />
         <ResourceInclude Source="Badge.axaml" />
         <ResourceInclude Source="Banner.axaml" />
         <ResourceInclude Source="ButtonGroup.axaml" />

src/Ursa/Common/LogicalHelpers.cs

@@ -0,0 +1,21 @@
+using Avalonia.LogicalTree;
+using Ursa.Controls;
+
+namespace Ursa.Common;
+
+public static class LogicalHelpers
+{
+    public static int CalculateDistanceFromLogicalParent<T, TItem>(TItem? item, int defaultValue = -1) 
+        where T : class 
+        where TItem : ILogical
+    {
+        var result = 0;
+        ILogical? logical = item;
+        while (logical is not null and not T)
+        {
+            if (logical is TItem) result++;
+            logical = logical.LogicalParent;
+        }
+        return item is not null ? result : defaultValue;
+    }
+}

src/Ursa/Common/VisualHelpers.cs

@@ -0,0 +1,14 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.VisualTree;
+
+namespace Ursa.Common;
+
+public static class VisualHelpers
+{
+    public static T? GetContainerFromEventSource<T>(this Visual? source) where T: Control
+    {
+        var item = source?.GetSelfAndVisualAncestors().OfType<T>().FirstOrDefault();
+        return item;
+    }
+}

src/Ursa/Controls/Anchor/Anchor.cs

@@ -0,0 +1,221 @@
+using Avalonia;
+using Avalonia.Animation;
+using Avalonia.Animation.Easings;
+using Avalonia.Controls;
+using Avalonia.Input;
+using Avalonia.Interactivity;
+using Avalonia.Styling;
+using Avalonia.VisualTree;
+using Ursa.Common;
+
+namespace Ursa.Controls;
+
+/// <summary>
+///     Some basic assumptions: This should not be a regular SelectingItemsControl, because it does not support multiple
+///     selections.
+///     Selection should not be exposed to the user, it is only used to determine which item is currently selected.
+///     The manipulation of container selection should be simplified.
+///     Scroll event of TargetContainer also triggers selection change.
+/// </summary>
+public class Anchor : ItemsControl
+{
+    public static readonly StyledProperty<ScrollViewer?> TargetContainerProperty =
+        AvaloniaProperty.Register<Anchor, ScrollViewer?>(
+            nameof(TargetContainer));
+
+    public static readonly AttachedProperty<string?> IdProperty =
+        AvaloniaProperty.RegisterAttached<Anchor, Visual, string?>("Id");
+
+    private CancellationTokenSource _cts = new();
+
+    private List<(string, double)> _positions = [];
+    private bool _scrollingFromSelection;
+
+    private AnchorItem? _selectedContainer;
+
+    public ScrollViewer? TargetContainer
+    {
+        get => GetValue(TargetContainerProperty);
+        set => SetValue(TargetContainerProperty, value);
+    }
+
+    public static void SetId(Visual obj, string? value)
+    {
+        obj.SetValue(IdProperty, value);
+    }
+
+    public static string? GetId(Visual obj)
+    {
+        return obj.GetValue(IdProperty);
+    }
+
+    public static readonly StyledProperty<double> TopOffsetProperty = AvaloniaProperty.Register<Anchor, double>(
+        nameof(TopOffset));
+
+    public double TopOffset
+    {
+        get => GetValue(TopOffsetProperty);
+        set => SetValue(TopOffsetProperty, value);
+    }
+    
+    protected override bool NeedsContainerOverride(object? item, int index, out object? recycleKey)
+    {
+        return NeedsContainer<AnchorItem>(item, out recycleKey);
+    }
+
+    protected override Control CreateContainerForItemOverride(object? item, int index, object? recycleKey)
+    {
+        var i = new AnchorItem();
+        return i;
+    }
+
+    private void ScrollToAnchor(Visual target)
+    {
+        if (TargetContainer is null)
+            return;
+
+        var targetPosition = target.TranslatePoint(new Point(0, 0), TargetContainer);
+        if (targetPosition.HasValue)
+        {
+            var from = TargetContainer.Offset.Y;
+            var to = TargetContainer.Offset.Y + targetPosition.Value.Y - TopOffset;
+            if (to > TargetContainer.Extent.Height - TargetContainer.Bounds.Height)
+                to = TargetContainer.Extent.Height - TargetContainer.Bounds.Height;
+            if (from == to) return;
+            var animation = new Animation
+            {
+                Duration = TimeSpan.FromSeconds(0.3),
+                Easing = new QuadraticEaseOut(),
+                Children =
+                {
+                    new KeyFrame
+                    {
+                        Setters = { new Setter(ScrollViewer.OffsetProperty, new Vector(0, from)) },
+                        Cue = new Cue(0.0)
+                    },
+                    new KeyFrame
+                    {
+                        Setters = { new Setter(ScrollViewer.OffsetProperty, new Vector(0, to)) },
+                        Cue = new Cue(1.0)
+                    }
+                }
+            };
+            _cts.Cancel();
+            _cts.Dispose();
+            _cts = new CancellationTokenSource();
+            var token = _cts.Token;
+            token.Register(_ => _scrollingFromSelection = false, null);
+            _scrollingFromSelection = true;
+            animation.RunAsync(TargetContainer, token).ContinueWith(_ => _scrollingFromSelection = false, token);
+        }
+    }
+
+    public void InvalidatePositions()
+    {
+        InvalidateAnchorPositions();
+        MarkSelectedContainerByPosition();
+    }
+
+    internal void InvalidateAnchorPositions()
+    {
+        if (TargetContainer is null) return;
+        var items = TargetContainer.GetVisualDescendants().Where(a => GetId(a) is not null);
+        var positions = new List<(string, double)>();
+        foreach (var item in items)
+        {
+            var anchorId = GetId(item);
+            if (anchorId is null) continue;
+            var position = item.TransformToVisual(TargetContainer)?.M32 + TargetContainer.Offset.Y;
+            if (position.HasValue) positions.Add((anchorId, position.Value));
+        }
+
+        positions.Sort((a, b) => a.Item2.CompareTo(b.Item2));
+        _positions = positions;
+    }
+
+    protected override void OnLoaded(RoutedEventArgs e)
+    {
+        base.OnLoaded(e);
+        var target = TargetContainer;
+        if (target is null) return;
+        TargetContainer?.AddHandler(ScrollViewer.ScrollChangedEvent, OnScrollChanged);
+        TargetContainer?.AddHandler(LoadedEvent, OnTargetContainerLoaded);
+        if (TargetContainer?.IsLoaded == true) InvalidateAnchorPositions();
+        MarkSelectedContainerByPosition();
+    }
+
+    private void OnScrollChanged(object? sender, ScrollChangedEventArgs e)
+    {
+        if (_scrollingFromSelection) return;
+        MarkSelectedContainerByPosition();
+    }
+
+    protected override void OnPointerPressed(PointerPressedEventArgs e)
+    {
+        base.OnPointerPressed(e);
+        var source = (e.Source as Visual).GetContainerFromEventSource<AnchorItem>();
+        if (source is null) return;
+        MarkSelectedContainer(source);
+        var target = TargetContainer?.GetVisualDescendants()
+                                    .FirstOrDefault(a => GetId(a) == source.AnchorId);
+        if (target is null) return;
+        ScrollToAnchor(target);
+    }
+
+    /// <summary>
+    ///     This method is used to expose the protected CreateContainerForItemOverride method to the AnchorItem class.
+    /// </summary>
+    internal Control CreateContainerForItemOverrideInternal(object? item, int index, object? recycleKey)
+    {
+        return CreateContainerForItemOverride(item, index, recycleKey);
+    }
+
+    internal bool NeedsContainerOverrideInternal(object? item, int index, out object? recycleKey)
+    {
+        return NeedsContainerOverride(item, index, out recycleKey);
+    }
+
+    internal void PrepareContainerForItemOverrideInternal(Control container, object? item, int index)
+    {
+        PrepareContainerForItemOverride(container, item, index);
+    }
+
+    internal void ContainerForItemPreparedOverrideInternal(Control container, object? item, int index)
+    {
+        ContainerForItemPreparedOverride(container, item, index);
+    }
+
+    internal void MarkSelectedContainer(AnchorItem? item)
+    {
+        var oldValue = _selectedContainer;
+        var newValue = item;
+        if (oldValue == newValue) return;
+        _selectedContainer?.SetValue(AnchorItem.IsSelectedProperty, false);
+        _selectedContainer = newValue;
+        _selectedContainer?.SetValue(AnchorItem.IsSelectedProperty, true);
+    }
+
+    internal void MarkSelectedContainerByPosition()
+    {
+        if (TargetContainer is null) return;
+        var top = TargetContainer.Offset.Y + TopOffset;
+        var topAnchorId = _positions.LastOrDefault(a => a.Item2 <= top).Item1;
+        if (topAnchorId is null) return;
+        var item = this.GetVisualDescendants().OfType<AnchorItem>()
+                       .FirstOrDefault(a => a.AnchorId == topAnchorId);
+        if (item is null) return;
+        MarkSelectedContainer(item);
+    }
+
+    protected override void OnUnloaded(RoutedEventArgs e)
+    {
+        base.OnUnloaded(e);
+        TargetContainer?.RemoveHandler(LoadedEvent, OnTargetContainerLoaded);
+        TargetContainer?.RemoveHandler(ScrollViewer.ScrollChangedEvent, OnScrollChanged);
+    }
+
+    private void OnTargetContainerLoaded(object? sender, RoutedEventArgs e)
+    {
+        InvalidateAnchorPositions();
+    }
+}

src/Ursa/Controls/Anchor/AnchorItem.cs

@@ -0,0 +1,91 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.Mixins;
+using Avalonia.Controls.Primitives;
+using Avalonia.Controls.Templates;
+using Avalonia.LogicalTree;
+using Ursa.Common;
+
+namespace Ursa.Controls;
+
+public class AnchorItem : HeaderedItemsControl, ISelectable
+{
+    public static readonly StyledProperty<string?> AnchorIdProperty = AvaloniaProperty.Register<AnchorItem, string?>(
+        nameof(AnchorId));
+
+    public static readonly StyledProperty<bool> IsSelectedProperty =
+        SelectingItemsControl.IsSelectedProperty.AddOwner<AnchorItem>();
+
+    private static readonly FuncTemplate<Panel?> DefaultPanel =
+        new(() => new StackPanel());
+
+    internal static readonly DirectProperty<AnchorItem, int> LevelProperty =
+        AvaloniaProperty.RegisterDirect<AnchorItem, int>(
+            nameof(Level), o => o.Level, (o, v) => o.Level = v);
+
+    private int _level;
+
+    private Anchor? _root;
+
+    static AnchorItem()
+    {
+        SelectableMixin.Attach<AnchorItem>(IsSelectedProperty);
+        PressedMixin.Attach<AnchorItem>();
+        ItemsPanelProperty.OverrideDefaultValue<AnchorItem>(DefaultPanel);
+    }
+
+    public int Level
+    {
+        get => _level;
+        set => SetAndRaise(LevelProperty, ref _level, value);
+    }
+
+    public string? AnchorId
+    {
+        get => GetValue(AnchorIdProperty);
+        set => SetValue(AnchorIdProperty, value);
+    }
+
+    public bool IsSelected
+    {
+        get => GetValue(IsSelectedProperty);
+        set => SetValue(IsSelectedProperty, value);
+    }
+
+    protected override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
+    {
+        base.OnAttachedToVisualTree(e);
+        _root = this.GetLogicalAncestors().OfType<Anchor>().FirstOrDefault();
+        Level = LogicalHelpers.CalculateDistanceFromLogicalParent<Anchor, AnchorItem>(this);
+        if (ItemTemplate is null && _root?.ItemTemplate is not null)
+            SetCurrentValue(ItemTemplateProperty, _root.ItemTemplate);
+
+        if (ItemContainerTheme is null && _root?.ItemContainerTheme is not null)
+            SetCurrentValue(ItemContainerThemeProperty, _root.ItemContainerTheme);
+    }
+
+    protected override Control CreateContainerForItemOverride(object? item, int index, object? recycleKey)
+    {
+        return EnsureRoot().CreateContainerForItemOverrideInternal(item, index, recycleKey);
+    }
+
+    protected override bool NeedsContainerOverride(object? item, int index, out object? recycleKey)
+    {
+        return EnsureRoot().NeedsContainerOverrideInternal(item, index, out recycleKey);
+    }
+
+    protected override void PrepareContainerForItemOverride(Control container, object? item, int index)
+    {
+        EnsureRoot().PrepareContainerForItemOverrideInternal(container, item, index);
+    }
+
+    protected override void ContainerForItemPreparedOverride(Control container, object? item, int index)
+    {
+        EnsureRoot().ContainerForItemPreparedOverrideInternal(container, item, index);
+    }
+
+    private Anchor EnsureRoot()
+    {
+        return _root ?? throw new InvalidOperationException("AnchorItem must be inside an Anchor control.");
+    }
+}