misc: add binding demo.

demo/Semi.Avalonia.Demo/Pages/TreeViewDemo.axaml

@@ -4,10 +4,13 @@
     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:vm="clr-namespace:Semi.Avalonia.Demo.Pages"
     d:DesignHeight="450"
     d:DesignWidth="800"
+    x:CompileBindings="True"
+    x:DataType="vm:TreeViewVm"
     mc:Ignorable="d">
-    <Panel HorizontalAlignment="Left">
+    <StackPanel HorizontalAlignment="Left">
         <TreeView>
             <TreeViewItem Header="Level 1">
                 <TreeViewItem Header="Level 2" />
@@ -42,5 +45,12 @@
                 </TreeViewItem>
             </TreeViewItem>
         </TreeView>
-    </Panel>
+        <TreeView ItemsSource="{Binding Items}">
+            <TreeView.ItemTemplate>
+                <TreeDataTemplate ItemsSource="{Binding Items}">
+                    <TextBlock Text="{Binding Name}" />
+                </TreeDataTemplate>
+            </TreeView.ItemTemplate>
+        </TreeView>
+    </StackPanel>
 </UserControl>

demo/Semi.Avalonia.Demo/Pages/TreeViewDemo.axaml.cs

@@ -1,6 +1,8 @@
+using System.Collections.ObjectModel;
 using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Markup.Xaml;
+using CommunityToolkit.Mvvm.ComponentModel;
 
 namespace Semi.Avalonia.Demo.Pages;
 
@@ -9,5 +11,34 @@ public partial class TreeViewDemo : UserControl
     public TreeViewDemo()
     {
         InitializeComponent();
+        this.DataContext = new TreeViewVm();
     }
+}
+
+public class TreeViewVm : ObservableObject
+{
+    public ObservableCollection<TreeViewItemVm> Items { get; set; }
+
+    public TreeViewVm()
+    {
+        Items = new ObservableCollection<TreeViewItemVm>()
+        {
+            new TreeViewItemVm() {Name = "Item 1", Id = "1"},
+            new TreeViewItemVm() {Name = "Item 2", Id = "2"},
+            new TreeViewItemVm() {Name = "Item 3", Id = "3", Items = new ObservableCollection<TreeViewItemVm>()
+            {
+                new TreeViewItemVm() {Name = "Item 3.1", Id = "3.1"},
+                new TreeViewItemVm() {Name = "Item 3.2", Id = "3.2"},
+                new TreeViewItemVm() {Name = "Item 3.3", Id = "3.3"},
+            },
+            },
+        };
+    }
+}
+
+public partial class TreeViewItemVm : ObservableObject
+{
+    public ObservableCollection<TreeViewItemVm> Items { get; set; }
+    public string Name { get; set; }
+    public string Id { get; set; }
 }