feat: wow, first prototype of navigation menu.

demo/Ursa.Demo/Pages/NavigationMenuDemo.axaml

@@ -0,0 +1,47 @@
+<UserControl
+    x:Class="Ursa.Demo.Pages.NavigationMenuDemo"
+    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"
+    xmlns:vm="clr-namespace:Ursa.Demo.ViewModels"
+    d:DesignHeight="450"
+    d:DesignWidth="800"
+    x:CompileBindings="True"
+    x:DataType="vm:NavigationMenuDemoViewModel"
+    mc:Ignorable="d">
+    <StackPanel>
+        <u:NavigationMenu Name="menu" ItemsSource="{Binding MenuItems}">
+            <u:NavigationMenu.ItemTemplate>
+                <DataTemplate>
+                    <u:NavigationMenuItem Header="{Binding MenuHeader}" ItemsSource="{Binding Children}" />
+                </DataTemplate>
+            </u:NavigationMenu.ItemTemplate>
+        </u:NavigationMenu>
+
+        <TreeView ItemsSource="{Binding MenuItems}">
+            <TreeView.ItemTemplate>
+                <TreeDataTemplate ItemsSource="{Binding Children}">
+                    <ContentControl Content="{Binding MenuHeader}" />
+                </TreeDataTemplate>
+            </TreeView.ItemTemplate>
+        </TreeView>
+
+        <TextBlock Text="{ReflectionBinding #menu.SelectedMenuItem.MenuHeader}" />
+
+        <u:NavigationMenu>
+            <u:NavigationMenuItem Header="111" />
+            <u:NavigationMenuItem Header="222" />
+            <u:NavigationMenuItem Header="333" />
+        </u:NavigationMenu>
+
+        <u:NavigationMenu ItemsSource="{Binding MenuItems}">
+            <u:NavigationMenu.ItemTemplate>
+                <DataTemplate>
+                    <u:NavigationMenuItem Header="{Binding MenuHeader}" />
+                </DataTemplate>
+            </u:NavigationMenu.ItemTemplate>
+        </u:NavigationMenu>
+    </StackPanel>
+</UserControl>

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

@@ -0,0 +1,15 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+using Ursa.Demo.ViewModels;
+
+namespace Ursa.Demo.Pages;
+
+public partial class NavigationMenuDemo : UserControl
+{
+    public NavigationMenuDemo()
+    {
+        InitializeComponent();
+        this.DataContext = new NavigationMenuDemoViewModel();
+    }
+}

demo/Ursa.Demo/ViewModels/NavigationMenuDemoViewModel.cs

@@ -0,0 +1,41 @@
+using System.Collections.ObjectModel;
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace Ursa.Demo.ViewModels;
+
+public class NavigationMenuDemoViewModel: ObservableObject
+{
+    public ObservableCollection<NavigationMenuItemViewModel> MenuItems { get; set; } = new()
+    {
+        new NavigationMenuItemViewModel()
+        {
+            MenuHeader = "1",
+            Children = new ObservableCollection<NavigationMenuItemViewModel>()
+            {
+                new NavigationMenuItemViewModel(){
+                    MenuHeader = "11" , 
+                    Children = new ObservableCollection<NavigationMenuItemViewModel>()
+                    {
+                        new NavigationMenuItemViewModel(){MenuHeader = "111"},
+                        new NavigationMenuItemViewModel(){MenuHeader = "112"}
+                    }},
+                new NavigationMenuItemViewModel(){MenuHeader = "12"}
+            }
+        },
+        new NavigationMenuItemViewModel()
+        {
+            MenuHeader = "2",
+            Children = new ObservableCollection<NavigationMenuItemViewModel>()
+            {
+                new NavigationMenuItemViewModel(){MenuHeader = "21"},
+                new NavigationMenuItemViewModel(){MenuHeader = "22"}
+            }
+        }
+    };
+}
+
+public class NavigationMenuItemViewModel: ObservableObject
+{
+    public string MenuHeader { get; set; }
+    public ObservableCollection<NavigationMenuItemViewModel> Children { get; set; } = new();
+}

demo/Ursa.Demo/Views/MainWindow.axaml

@@ -35,6 +35,9 @@
             <TabItem Header="IPv4Box">
                 <pages:IPv4BoxDemo />
             </TabItem>
+            <TabItem Header="Navigation">
+                <pages:NavigationMenuDemo />
+            </TabItem>
             <TabItem Header="Pagination">
                 <pages:PaginationDemo />
             </TabItem>