feat: update click behavior.

demo/Ursa.Demo/Pages/TreeComboBoxDemo.axaml

@@ -9,7 +9,11 @@
     <StackPanel>
         <u:TreeComboBox>
             <u:TreeComboBoxItem Header="Hello">
-                <u:TreeComboBoxItem Header="Hello World"/>
+                <u:TreeComboBoxItem Header="Hello World">
+                    <u:TreeComboBoxItem Header="Hello World 1"/>
+                    <u:TreeComboBoxItem Header="Hello World 2"/>
+                    <u:TreeComboBoxItem Header="Hello World 3"/>
+                </u:TreeComboBoxItem>
                 <u:TreeComboBoxItem Header="Hello Avalonia"/>
                 <u:TreeComboBoxItem Header="Hello Another"/>
             </u:TreeComboBoxItem>

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

@@ -1,17 +1,19 @@
 <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">
+                    xmlns:iri="https://irihi.tech/shared"
+                    xmlns:converters="clr-namespace:Avalonia.Controls.Converters;assembly=Avalonia.Controls">
     <!-- Add Resources Here -->
     
+    <converters:MarginMultiplierConverter x:Key="LeftMarginConverter" Indent="20" Left="True"/>
+    
     <ControlTheme x:Key="{x:Type u:TreeComboBox}" TargetType="u:TreeComboBox">
         <Setter Property="Template">
             <ControlTemplate TargetType="u:TreeComboBox">
-                <Grid ColumnDefinitions="*, Auto, 32">
+                <Grid ColumnDefinitions="*, Auto, 32" Background="Transparent">
-                    <Border Grid.Column="0" Grid.ColumnSpan="3" Background="Red"></Border>
+                    <Border Grid.Column="0" Grid.ColumnSpan="3" Background="Transparent" BorderBrush="Blue" BorderThickness="1" CornerRadius="3"/>
                     <ContentPresenter Grid.Column="0" MinHeight="32" Content="{TemplateBinding SelectionBoxItem}"/>
-                    
+                    <Popup Name="{x:Static iri:PartNames.PART_Popup}" Grid.Column="0" IsLightDismissEnabled="True" IsOpen="{Binding IsDropDownOpen, RelativeSource={RelativeSource TemplatedParent}}">
-                    <Popup Grid.Column="0" IsOpen="{Binding IsDropDownOpen, RelativeSource={RelativeSource TemplatedParent}}">
                         <Border Background="{DynamicResource ComboBoxPopupBackground}">
                             <ScrollViewer>
                                 <ItemsPresenter ItemsPanel="{TemplateBinding ItemsPanel}"/>
@@ -28,12 +30,15 @@
             <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, *">
+                        <Grid
-                            <ToggleButton Name="PART_ExpandCollapseChevron" Grid.Column="0" Focusable="False"></ToggleButton>
+                            Name="{x:Static iri:PartNames.PART_Header}"
+                            Margin="{TemplateBinding Level, Mode=OneWay, Converter={StaticResource LeftMarginConverter}}" 
+                              ColumnDefinitions="Auto, *">
+                            <ToggleButton IsChecked="{TemplateBinding IsExpanded, Mode=TwoWay}" Theme="{DynamicResource ToggleButtonTreeViewItemIconButton}" 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}"/>
+                    <ItemsPresenter IsVisible="{TemplateBinding IsExpanded}" Name="{x:Static iri:PartNames.PART_ItemsPresenter}" ItemsPanel="{TemplateBinding ItemsPanel}"/>
                 </StackPanel>
             </ControlTemplate>
         </Setter>

src/Ursa/Controls/ComboBox/TreeComboBox.cs

@@ -15,6 +15,8 @@ namespace Ursa.Controls;
 [TemplatePart(PartNames.PART_Popup, typeof(Popup))]
 public class TreeComboBox: SelectingItemsControl
 {
+    private Popup? _popup;
+    
     private static readonly FuncTemplate<Panel?> DefaultPanel =
         new FuncTemplate<Panel?>(() => new VirtualizingStackPanel());
 
@@ -87,6 +89,12 @@ public class TreeComboBox: SelectingItemsControl
         FocusableProperty.OverrideDefaultValue<TreeComboBox>(true);
     }
 
+    protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
+    {
+        base.OnApplyTemplate(e);
+        _popup = e.NameScope.Find<Popup>(PartNames.PART_Popup);
+    }
+
     protected override bool NeedsContainerOverride(object? item, int index, out object? recycleKey)
     {
         return NeedsContainer<TreeComboBoxItem>(item, out recycleKey);
@@ -122,7 +130,16 @@ public class TreeComboBox: SelectingItemsControl
         base.OnPointerReleased(e);
         if (e.InitialPressMouseButton == MouseButton.Left)
         {
-            IsDropDownOpen = !IsDropDownOpen;
+            if (_popup is not null && _popup.IsOpen && e.Source is TextBlock v && _popup.IsInsidePopup(v))
+            {
+                SelectionBoxItem = v.Text;
+                SetCurrentValue(IsDropDownOpenProperty, false);
+            }
+            else
+            {
+                IsDropDownOpen = !IsDropDownOpen;
+            }
+            
         }
     }
 } 

src/Ursa/Controls/ComboBox/TreeComboBoxItem.cs

@@ -3,6 +3,7 @@ using Avalonia.Controls;
 using Avalonia.Controls.Metadata;
 using Avalonia.Controls.Primitives;
 using Avalonia.Input;
+using Avalonia.Interactivity;
 using Avalonia.LogicalTree;
 using Avalonia.Media;
 using Avalonia.Media.TextFormatting;
@@ -47,9 +48,9 @@ public class TreeComboBoxItem: HeaderedItemsControl, ISelectable
     protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
     {
         base.OnApplyTemplate(e);
-        DoubleTappedEvent.RemoveHandler(OnDoubleTapped, _header);
+        DoubleTappedEvent.RemoveHandler(OnDoubleTapped, this);
         _header = e.NameScope.Find<Control>(PartNames.PART_Header);
-        DoubleTappedEvent.AddHandler(OnDoubleTapped, _header);
+        DoubleTappedEvent.AddHandler(OnDoubleTapped, RoutingStrategies.Tunnel, true, this);
     }
 
     protected override void OnAttachedToLogicalTree(LogicalTreeAttachmentEventArgs e)