feat: add demo. update overrides with internal implementations.

demo/Ursa.Demo/Pages/TreeComboBoxDemo.axaml

@@ -0,0 +1,23 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             xmlns:u="https://irihi.tech/ursa"
+             mc:Ignorable="d" d:DesignWidth="800"
+             d:DesignHeight="450"
+             x:Class="Ursa.Demo.Pages.TreeComboBoxDemo">
+    <StackPanel>
+        <u:TreeComboBox>
+            <u:TreeComboBoxItem Header="Hello">
+                <u:TreeComboBoxItem Header="Hello World"/>
+                <u:TreeComboBoxItem Header="Hello Avalonia"/>
+                <u:TreeComboBoxItem Header="Hello Another"/>
+            </u:TreeComboBoxItem>
+            <u:TreeComboBoxItem Header="World">
+                <u:TreeComboBoxItem Header="World Hello"/>
+                <u:TreeComboBoxItem Header="World Avalonia"/>
+                <u:TreeComboBoxItem Header="World Another"/>
+            </u:TreeComboBoxItem>
+        </u:TreeComboBox>
+    </StackPanel>
+</UserControl>

demo/Ursa.Demo/Pages/TreeComboBoxDemo.axaml.cs

@@ -0,0 +1,13 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace Ursa.Demo.Pages;
+
+public partial class TreeComboBoxDemo : UserControl
+{
+    public TreeComboBoxDemo()
+    {
+        InitializeComponent();
+    }
+}

demo/Ursa.Demo/ViewModels/MainViewViewModel.cs

@@ -55,6 +55,7 @@ public class MainViewViewModel : ViewModelBase
             MenuKeys.MenuKeySkeleton => new SkeletonDemoViewModel(),
             MenuKeys.MenuKeyTagInput => new TagInputDemoViewModel(),
             MenuKeys.MenuKeyTimeline => new TimelineDemoViewModel(),
+            MenuKeys.MenuKeyTreeComboBox => new TreeComboBoxDemoViewModel(),
             MenuKeys.MenuKeyTwoTonePathIcon => new TwoTonePathIconDemoViewModel(),
             MenuKeys.MenuKeyThemeToggler => new ThemeTogglerDemoViewModel(),
             MenuKeys.MenuKeyToolBar => new ToolBarDemoViewModel(),

demo/Ursa.Demo/ViewModels/MenuViewModel.cs

@@ -43,6 +43,7 @@ public class MenuViewModel: ViewModelBase
             new() { MenuHeader = "TagInput", Key = MenuKeys.MenuKeyTagInput },
             new() { MenuHeader = "Theme Toggler", Key = MenuKeys.MenuKeyThemeToggler },
             new() { MenuHeader = "Timeline", Key = MenuKeys.MenuKeyTimeline },
+            new() { MenuHeader = "TreeComboBox", Key = MenuKeys.MenuKeyTreeComboBox },
             new() { MenuHeader = "TwoTonePathIcon", Key = MenuKeys.MenuKeyTwoTonePathIcon},
             new() { MenuHeader = "ToolBar", Key = MenuKeys.MenuKeyToolBar },
             new() { MenuHeader = "Verification Code", Key = MenuKeys.MenuKeyVerificationCode, Status = "New" },
@@ -85,6 +86,7 @@ public static class MenuKeys
     public const string MenuKeyTimeline = "Timeline";
     public const string MenuKeyTwoTonePathIcon = "TwoTonePathIcon";
     public const string MenuKeyThemeToggler = "ThemeToggler";
+    public const string MenuKeyTreeComboBox = "TreeComboBox";
     public const string MenuKeyToolBar = "ToolBar";
     public const string MenuKeyVerificationCode = "VerificationCode";
 

demo/Ursa.Demo/ViewModels/TreeComboBoxDemoViewModel.cs

@@ -0,0 +1,8 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace Ursa.Demo.ViewModels;
+
+public class TreeComboBoxDemoViewModel: ObservableObject
+{
+    
+}

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

@@ -0,0 +1,41 @@
+<ResourceDictionary xmlns="https://github.com/avaloniaui"
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    xmlns:u="https://irihi.tech/ursa"
+                    xmlns:iri="https://irihi.tech/shared">
+    <!-- Add Resources Here -->
+    
+    <ControlTheme x:Key="{x:Type u:TreeComboBox}" TargetType="u:TreeComboBox">
+        <Setter Property="Template">
+            <ControlTemplate TargetType="u:TreeComboBox">
+                <Grid ColumnDefinitions="*, Auto, 32">
+                    <Border Grid.Column="0" Grid.ColumnSpan="3" Background="Red"></Border>
+                    <ContentPresenter Grid.Column="0" MinHeight="32" Content="{TemplateBinding SelectionBoxItem}"/>
+                    
+                    <Popup Grid.Column="0" IsOpen="{Binding IsDropDownOpen, RelativeSource={RelativeSource TemplatedParent}}">
+                        <Border Background="{DynamicResource ComboBoxPopupBackground}">
+                            <ScrollViewer>
+                                <ItemsPresenter ItemsPanel="{TemplateBinding ItemsPanel}"/>
+                            </ScrollViewer>
+                        </Border>
+                    </Popup>
+                </Grid>
+            </ControlTemplate>
+        </Setter>
+    </ControlTheme>
+    
+    <ControlTheme x:Key="{x:Type u:TreeComboBoxItem}" TargetType="u:TreeComboBoxItem">
+        <Setter Property="Template">
+            <ControlTemplate TargetType="u:TreeComboBoxItem">
+                <StackPanel>
+                    <Border Name="PART_LayoutRoot" MinHeight="{TemplateBinding MinHeight}" TemplatedControl.IsTemplateFocusTarget="True">
+                        <Grid Name="{x:Static iri:PartNames.PART_Header}" Margin="10" ColumnDefinitions="Auto, *">
+                            <ToggleButton Name="PART_ExpandCollapseChevron" Grid.Column="0" Focusable="False"></ToggleButton>
+                            <ContentPresenter Grid.Column="1" Name="{x:Static iri:PartNames.PART_HeaderPresenter}" Content="{TemplateBinding Header}" ContentTemplate="{TemplateBinding HeaderTemplate}" Focusable="False"/>
+                        </Grid>
+                    </Border>
+                    <ItemsPresenter Name="{x:Static iri:PartNames.PART_ItemsPresenter}" ItemsPanel="{TemplateBinding ItemsPanel}"/>
+                </StackPanel>
+            </ControlTemplate>
+        </Setter>
+    </ControlTheme>
+</ResourceDictionary>

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

@@ -32,6 +32,7 @@
         <ResourceInclude Source="TagInput.axaml" />
         <ResourceInclude Source="ThemeSelector.axaml" />
         <ResourceInclude Source="Timeline.axaml" />
+        <ResourceInclude Source="TreeComboBox.axaml"/>
         <ResourceInclude Source="Skeleton.axaml" />
         <ResourceInclude Source="TwoTonePathIcon.axaml" />
         <ResourceInclude Source="ToolBar.axaml" />

src/Ursa/Controls/ComboBox/TreeComboBox.cs

@@ -0,0 +1,128 @@
+using System.Data;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.Metadata;
+using Avalonia.Controls.Primitives;
+using Avalonia.Controls.Templates;
+using Avalonia.Input;
+using Avalonia.Layout;
+using Avalonia.OpenGL.Controls;
+using Irihi.Avalonia.Shared.Common;
+
+
+namespace Ursa.Controls;
+
+[TemplatePart(PartNames.PART_Popup, typeof(Popup))]
+public class TreeComboBox: SelectingItemsControl
+{
+    private static readonly FuncTemplate<Panel?> DefaultPanel =
+        new FuncTemplate<Panel?>(() => new VirtualizingStackPanel());
+
+    public static readonly StyledProperty<double> MaxDropDownHeightProperty =
+        ComboBox.MaxDropDownHeightProperty.AddOwner<TreeComboBox>();
+
+    public double MaxDropDownHeight
+    {
+        get => GetValue(MaxDropDownHeightProperty);
+        set => SetValue(MaxDropDownHeightProperty, value);
+    }
+
+    public static readonly StyledProperty<string?> WatermarkProperty =
+        TextBox.WatermarkProperty.AddOwner<TreeComboBox>();
+
+    public string? Watermark
+    {
+        get => GetValue(WatermarkProperty);
+        set => SetValue(WatermarkProperty, value);
+    }
+    
+    public static readonly StyledProperty<bool> IsDropDownOpenProperty =
+        ComboBox.IsDropDownOpenProperty.AddOwner<TreeComboBox>();
+    
+    public bool IsDropDownOpen
+    {
+        get => GetValue(IsDropDownOpenProperty);
+        set => SetValue(IsDropDownOpenProperty, value);
+    }
+
+    public static readonly StyledProperty<HorizontalAlignment> HorizontalContentAlignmentProperty =
+        ContentControl.HorizontalContentAlignmentProperty.AddOwner<TreeComboBox>();
+
+    public HorizontalAlignment HorizontalContentAlignment
+    {
+        get => GetValue(HorizontalContentAlignmentProperty);
+        set => SetValue(HorizontalContentAlignmentProperty, value);
+    }
+    
+    public static readonly StyledProperty<VerticalAlignment> VerticalContentAlignmentProperty =
+        ContentControl.VerticalContentAlignmentProperty.AddOwner<TreeComboBox>();
+    
+    public VerticalAlignment VerticalContentAlignment
+    {
+        get => GetValue(VerticalContentAlignmentProperty);
+        set => SetValue(VerticalContentAlignmentProperty, value);
+    }
+
+    public static readonly StyledProperty<IDataTemplate?> SelectedItemTemplateProperty =
+        AvaloniaProperty.Register<TreeComboBox, IDataTemplate?>(nameof(SelectedItemTemplate));
+
+    public IDataTemplate? SelectedItemTemplate
+    {
+        get => GetValue(SelectedItemTemplateProperty);
+        set => SetValue(SelectedItemTemplateProperty, value);
+    }
+
+    public static readonly DirectProperty<TreeComboBox, object?> SelectionBoxItemProperty = AvaloniaProperty.RegisterDirect<TreeComboBox, object?>(
+        nameof(SelectionBoxItem), o => o.SelectionBoxItem);
+    private object? _selectionBoxItem;
+    public object? SelectionBoxItem
+    {
+        get => _selectionBoxItem;
+        protected set => SetAndRaise(SelectionBoxItemProperty, ref _selectionBoxItem, value);
+    }
+    
+    static TreeComboBox()
+    {
+        ItemsPanelProperty.OverrideDefaultValue<TreeComboBox>(DefaultPanel);
+        FocusableProperty.OverrideDefaultValue<TreeComboBox>(true);
+    }
+
+    protected override bool NeedsContainerOverride(object? item, int index, out object? recycleKey)
+    {
+        return NeedsContainer<TreeComboBoxItem>(item, out recycleKey);
+    }
+
+    internal bool NeedsContainerInternal(object? item, int index, out object? recycleKey)
+    {
+        return NeedsContainerOverride(item, index, out recycleKey);
+    }
+
+    protected override Control CreateContainerForItemOverride(object? item, int index, object? recycleKey)
+    {
+        return new TreeComboBoxItem();
+    }
+
+    internal Control CreateContainerForItemInternal(object? item, int index, object? recycleKey)
+    {
+        return CreateContainerForItemOverride(item, index, recycleKey);
+    }
+
+    protected override void ContainerForItemPreparedOverride(Control container, object? item, int index)
+    {
+        base.ContainerForItemPreparedOverride(container, item, index);
+    }
+
+    internal void ContainerForItemPreparedInternal(Control container, object? item, int index)
+    {
+        ContainerForItemPreparedOverride(container, item, index);
+    }
+
+    protected override void OnPointerReleased(PointerReleasedEventArgs e)
+    {
+        base.OnPointerReleased(e);
+        if (e.InitialPressMouseButton == MouseButton.Left)
+        {
+            IsDropDownOpen = !IsDropDownOpen;
+        }
+    }
+} 

src/Ursa/Controls/ComboBox/TreeComboBoxItem.cs

@@ -0,0 +1,110 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.Metadata;
+using Avalonia.Controls.Primitives;
+using Avalonia.Input;
+using Avalonia.LogicalTree;
+using Avalonia.Media;
+using Avalonia.Media.TextFormatting;
+using Irihi.Avalonia.Shared.Common;
+using Irihi.Avalonia.Shared.Helpers;
+
+namespace Ursa.Controls;
+
+[TemplatePart(PartNames.PART_Header, typeof(Control))]
+public class TreeComboBoxItem: HeaderedItemsControl, ISelectable
+{
+    private Control? _header;
+    private TreeComboBox? _treeComboBox;
+    
+    public static readonly StyledProperty<bool> IsSelectedProperty = TreeViewItem.IsSelectedProperty.AddOwner<TreeComboBoxItem>();
+
+    public bool IsSelected
+    {
+        get => GetValue(IsSelectedProperty);
+        set => SetValue(IsSelectedProperty, value);
+    }
+    
+    public static readonly StyledProperty<bool> IsExpandedProperty = TreeViewItem.IsExpandedProperty.AddOwner<TreeComboBoxItem>();
+    
+    public bool IsExpanded
+    {
+        get => GetValue(IsExpandedProperty);
+        set => SetValue(IsExpandedProperty, value);
+    }
+
+    
+
+    public static readonly DirectProperty<TreeComboBoxItem, int> LevelProperty = AvaloniaProperty.RegisterDirect<TreeComboBoxItem, int>(
+        nameof(Level), o => o.Level, (o, v) => o.Level = v);
+    private int _level;
+    public int Level
+    {
+        get => _level;
+        protected set => SetAndRaise(LevelProperty, ref _level, value);
+    }
+
+    protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
+    {
+        base.OnApplyTemplate(e);
+        DoubleTappedEvent.RemoveHandler(OnDoubleTapped, _header);
+        _header = e.NameScope.Find<Control>(PartNames.PART_Header);
+        DoubleTappedEvent.AddHandler(OnDoubleTapped, _header);
+    }
+
+    protected override void OnAttachedToLogicalTree(LogicalTreeAttachmentEventArgs e)
+    {
+        base.OnAttachedToLogicalTree(e);
+        _treeComboBox = this.FindLogicalAncestorOfType<TreeComboBox>();
+        Level = CalculateDistanceFromLogicalParent<TreeComboBox>(this);
+        if (this.ItemTemplate is null && this._treeComboBox?.ItemTemplate is not null)
+        {
+            SetCurrentValue(ItemTemplateProperty, this._treeComboBox.ItemTemplate);
+        }
+        
+        
+        
+    }
+
+    private void OnDoubleTapped(object sender, TappedEventArgs e)
+    {
+        if (this.ItemCount <= 0) return;
+        this.SetCurrentValue(IsExpandedProperty, !IsExpanded);
+        e.Handled = true;
+    }
+
+    protected override bool NeedsContainerOverride(object? item, int index, out object? recycleKey)
+    {
+        return EnsureParent().NeedsContainerInternal(item, index, out recycleKey);
+    }
+
+    protected override Control CreateContainerForItemOverride(object? item, int index, object? recycleKey)
+    {
+        return EnsureParent().CreateContainerForItemInternal(item, index, recycleKey);
+    }
+
+    protected override void ContainerForItemPreparedOverride(Control container, object? item, int index)
+    {
+        EnsureParent().ContainerForItemPreparedInternal(container, item, index);
+    }
+
+    // TODO replace with helper method from shared library. 
+    private static int CalculateDistanceFromLogicalParent<T>(ILogical? logical, int @default = -1) where T: ILogical
+    {
+        int distance = 0;
+        ILogical? parent = logical;
+        while (parent is not null)
+        {
+            if (parent is T) return distance;
+            parent = parent.LogicalParent;
+            distance++;
+        }
+        return @default;
+    }
+
+    private TreeComboBox EnsureParent()
+    {
+        return this._treeComboBox ??
+               throw new InvalidOperationException("TreeComboBoxItem must be a part of TreeComboBox");
+    }
+}

src/Ursa/Ursa.csproj

@@ -17,7 +17,7 @@
 
     <ItemGroup>
         <PackageReference Include="Avalonia" Version="$(AvaloniaVersion)"/>
-        <PackageReference Include="Irihi.Avalonia.Shared" Version="0.1.5"/>
+        <PackageReference Include="Irihi.Avalonia.Shared" Version="0.1.6" />
     </ItemGroup>
 
     <ItemGroup>