chore: add avalonia DataValidationErrors demo.

src/Avalonia/HandyControlDemo_Avalonia/ViewModel/Common/InputElementDemoViewModel.cs

@@ -0,0 +1,19 @@
+using System.ComponentModel.DataAnnotations;
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace HandyControlDemo.ViewModel;
+
+public partial class InputElementDemoViewModel : ObservableValidator
+{
+    [Required] [EmailAddress] [ObservableProperty] [NotifyDataErrorInfo]
+    private string? _email1;
+
+    [Required] [EmailAddress] [ObservableProperty] [NotifyDataErrorInfo]
+    private string? _email2;
+
+    [Required] [ObservableProperty] [NotifyDataErrorInfo]
+    private string? _text1;
+
+    [Required] [ObservableProperty] [NotifyDataErrorInfo]
+    private string? _text2;
+}

src/Avalonia/HandyControlDemo_Avalonia/ViewModel/DemoViewModelBase`1.cs

@@ -3,13 +3,7 @@ using CommunityToolkit.Mvvm.ComponentModel;
 
 namespace HandyControlDemo.ViewModel;
 
-public class DemoViewModelBase<T> : ObservableObject
+public partial class DemoViewModelBase<T> : ObservableObject
 {
-    private IList<T> _dataList = [];
-
-    public IList<T> DataList
-    {
-        get => _dataList;
-        set => SetProperty(ref _dataList, value);
-    }
+    [ObservableProperty] private IList<T> _dataList = [];
 }

src/Avalonia/HandyControlDemo_Avalonia/ViewModel/ViewModelLocator.cs

@@ -19,9 +19,12 @@ public class ViewModelLocator
 
         services.AddSingleton<DataService>();
         services.AddTransient<MainViewModel>();
+        services.AddTransient<InputElementDemoViewModel>();
 
         _serviceProvider = services.BuildServiceProvider();
     }
 
     public MainViewModel Main => _serviceProvider.GetService<MainViewModel>()!;
+
+    public InputElementDemoViewModel InputElementDemo => _serviceProvider.GetService<InputElementDemoViewModel>()!;
 }