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

demo/Ursa.Demo/DataTemplates/ToolBarItemTemplateSelector.cs

@@ -0,0 +1,48 @@
+using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
+using Avalonia.Controls.Templates;
+using Avalonia.Data;
+using Ursa.Demo.ViewModels;
+
+namespace Ursa.Demo.Converters;
+
+public class ToolBarItemTemplateSelector: IDataTemplate
+{
+    public static ToolBarItemTemplateSelector Instance { get; } = new();
+    public Control? Build(object? param)
+    {
+        if (param is null) return null;
+        if (param is ToolBarButtonItemViewModel vm)
+        {
+            return new Button()
+            {
+                [!ContentControl.ContentProperty] = new Binding() { Path = "Content" },
+                [!Button.CommandProperty] = new Binding() { Path = "Command" },
+            };
+        }
+        if (param is ToolBarCheckBoxItemViweModel cb)
+        {
+            return new CheckBox()
+            {
+                [!ContentControl.ContentProperty] = new Binding() { Path = "Content" },
+                [!ToggleButton.IsCheckedProperty] = new Binding() { Path = "IsChecked" },
+                [!Button.CommandProperty] = new Binding() { Path = "Command" },
+            };
+        }
+        if (param is ToolBarComboBoxItemViewModel combo)
+        {
+            return new ComboBox()
+            {
+                [!ContentControl.ContentProperty] = new Binding() { Path = "Content" },
+                [!SelectingItemsControl.SelectedItemProperty] = new Binding() { Path = "SelectedItem" },
+                [!ItemsControl.ItemsSourceProperty] = new Binding() { Path = "Items" },
+            };
+        }
+        return new Button() { Content = "Undefined Item" };
+    }
+
+    public bool Match(object? data)
+    {
+        return data is ToolBarItemViewModel;
+    }
+}