feat: initialize, setup demo. make sure MVVM works.

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

@@ -0,0 +1,37 @@
+<ResourceDictionary
+    xmlns="https://github.com/avaloniaui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:u="https://irihi.tech/ursa">
+    <!--  Add Resources Here  -->
+    <ControlTheme x:Key="{x:Type u:ToolBar}" TargetType="u:ToolBar">
+        <Setter Property="ItemsPanel">
+            <ItemsPanelTemplate>
+                <u:ToolBarPanel/>
+            </ItemsPanelTemplate>
+        </Setter>
+        <Setter Property="Template">
+            <ControlTemplate TargetType="u:ToolBar">
+                <Border
+                    Padding="2"
+                    Theme="{DynamicResource CardBorder}"
+                    CornerRadius="4">
+                    <StackPanel Orientation="{TemplateBinding Orientation}">
+                        <Rectangle
+                            Width="1"
+                            VerticalAlignment="Stretch"
+                            Margin="4 0"
+                            Fill="Gray" />
+                        <ContentPresenter Margin="4 0" Content="{TemplateBinding Header}" ContentTemplate="{TemplateBinding HeaderTemplate}" />
+                        <ItemsPresenter VerticalAlignment="Center" HorizontalAlignment="Left" ItemsPanel="{TemplateBinding ItemsPanel}"/>
+                        <Button Content="More"></Button>
+                        <Popup>
+                            <Border Theme="{DynamicResource CardBorder}">
+                                <StackPanel Name="{x:Static u:ToolBar.PART_OverflowPanel}"></StackPanel>
+                            </Border>
+                        </Popup>
+                    </StackPanel>
+                </Border>
+            </ControlTemplate>
+        </Setter>
+    </ControlTheme>
+</ResourceDictionary>

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

@@ -30,5 +30,6 @@
         <ResourceInclude Source="ThemeSelector.axaml" />
         <ResourceInclude Source="Timeline.axaml" />
         <ResourceInclude Source="TwoTonePathIcon.axaml" />
+        <ResourceInclude Source="ToolBar.axaml" />
     </ResourceDictionary.MergedDictionaries>
 </ResourceDictionary>

src/Ursa/Controls/ToolBar/OverflowMode.cs

@@ -0,0 +1,8 @@
+namespace Ursa.Controls;
+
+public enum OverflowMode
+{
+    AsNeeded,
+    Always,
+    Never
+}

src/Ursa/Controls/ToolBar/ToolBar.cs

@@ -0,0 +1,61 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.Metadata;
+using Avalonia.Controls.Presenters;
+using Avalonia.Controls.Primitives;
+using Avalonia.Controls.Templates;
+using Avalonia.Layout;
+
+namespace Ursa.Controls;
+
+[TemplatePart(PART_OverflowPanel, typeof(Panel))]
+public class ToolBar: HeaderedItemsControl
+{
+    public const string PART_OverflowPanel = "PART_OverflowPanel";
+    
+    internal Panel? OverflowPanel { get; private set; }
+    
+    private static readonly ITemplate<Panel?> DefaultTemplate =
+        new FuncTemplate<Panel?>(() => new ToolBarPanel() { Orientation = Orientation.Horizontal });
+    
+    public static readonly StyledProperty<Orientation> OrientationProperty =
+        StackPanel.OrientationProperty.AddOwner<ToolBar>();
+
+    public Orientation Orientation
+    {
+        get => GetValue(OrientationProperty);
+        set => SetValue(OrientationProperty, value);
+    }
+    
+    public static readonly StyledProperty<int> BandProperty = AvaloniaProperty.Register<ToolBar, int>(
+        nameof(Band));
+    
+    public int Band
+    {
+        get => GetValue(BandProperty);
+        set => SetValue(BandProperty, value);
+    }
+
+    static ToolBar()
+    {
+        IsTabStopProperty.OverrideDefaultValue<ToolBar>(false);
+        ItemsPanelProperty.OverrideDefaultValue<ToolBar>(DefaultTemplate);
+        OrientationProperty.OverrideDefaultValue<ToolBar>(Orientation.Horizontal);
+    }
+    
+    protected override bool NeedsContainerOverride(object? item, int index, out object? recycleKey)
+    {
+        return NeedsContainer<Control>(item, out recycleKey);
+    }
+
+    protected override Control CreateContainerForItemOverride(object? item, int index, object? recycleKey)
+    {
+        return new ContentPresenter();
+    }
+
+    protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
+    {
+        base.OnApplyTemplate(e);
+        OverflowPanel = e.NameScope.Find<Panel>(PART_OverflowPanel);
+    }
+}

src/Ursa/Controls/ToolBar/ToolBarOverflowPanel.cs

@@ -0,0 +1,8 @@
+using Avalonia.Controls;
+
+namespace Ursa.Controls;
+
+public class ToolBarOverflowPanel: StackPanel
+{
+    
+}

src/Ursa/Controls/ToolBar/ToolBarPanel.cs

@@ -0,0 +1,34 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Layout;
+using Avalonia.LogicalTree;
+
+namespace Ursa.Controls;
+
+public class ToolBarPanel: StackPanel
+{
+    private ToolBar? _parent;
+    private Panel? _overflowPanel;
+
+    internal Panel? OverflowPanel => _overflowPanel ??= _parent?.OverflowPanel;
+    internal ToolBar? ParentToolBar => _parent ??= this.TemplatedParent as ToolBar;
+
+    static ToolBarPanel()
+    {
+        OrientationProperty.OverrideDefaultValue<ToolBarPanel>(Orientation.Horizontal);
+    }
+
+    protected override void OnAttachedToLogicalTree(LogicalTreeAttachmentEventArgs e)
+    {
+        base.OnAttachedToLogicalTree(e);
+        _parent = this.TemplatedParent as ToolBar;
+        if (_parent is null) return;
+        this[!OrientationProperty] = _parent[!OrientationProperty];
+    }
+
+    protected override Size MeasureOverride(Size availableSize)
+    {
+        return base.MeasureOverride(availableSize);
+        
+    }
+}

src/Ursa/Ursa.csproj

@@ -17,4 +17,8 @@
         <PackageReference Include="Irihi.Avalonia.Shared" Version="0.1.2" />
     </ItemGroup>
 
+    <ItemGroup>
+      <Folder Include="Controls\Panels\" />
+    </ItemGroup>
+
 </Project>