AutoCompleteBox validation not working for SelectedItem #5586

src/Avalonia.Controls/AutoCompleteBox.cs

@@ -483,7 +483,9 @@ namespace Avalonia.Controls
             AvaloniaProperty.RegisterDirect<AutoCompleteBox, object>(
                 nameof(SelectedItem),
                 o => o.SelectedItem,
-                (o, v) => o.SelectedItem = v);
+                (o, v) => o.SelectedItem = v,
+                defaultBindingMode: BindingMode.TwoWay,
+                enableDataValidation: true);
 
         /// <summary>
         /// Identifies the
@@ -1333,7 +1335,7 @@ namespace Avalonia.Controls
 
             base.OnApplyTemplate(e);
         }
-        
+
         /// <summary>
         /// Called to update the validation state for properties for which data validation is
         /// enabled.
@@ -1342,7 +1344,7 @@ namespace Avalonia.Controls
         /// <param name="value">The new binding value for the property.</param>
         protected override void UpdateDataValidation<T>(AvaloniaProperty<T> property, BindingValue<T> value)
         {
-            if (property == TextProperty)
+            if (property == TextProperty || property == SelectedItemProperty)
             {
                 DataValidationErrors.SetError(this, value.Error);
             }

tests/Avalonia.Controls.UnitTests/AutoCompleteBoxTests.cs

@@ -14,6 +14,8 @@ using Avalonia.UnitTests;
 using Moq;
 using Xunit;
 using System.Collections.ObjectModel;
+using System.Reactive.Linq;
+using System.Reactive.Subjects;
 
 namespace Avalonia.Controls.UnitTests
 {
@@ -396,6 +398,36 @@ namespace Avalonia.Controls.UnitTests
                 Assert.Equal(control.Text, control.ItemSelector(input, selectedItem));
             });
         }
+        
+        [Fact]
+        public void Text_Validation()
+        {
+            RunTest((control, textbox) =>
+            {
+                var exception = new InvalidCastException("failed validation");
+                var textObservable = new BehaviorSubject<BindingNotification>(new BindingNotification(exception, BindingErrorType.DataValidationError));
+                control.Bind(AutoCompleteBox.TextProperty, textObservable);
+                Dispatcher.UIThread.RunJobs();
+
+                Assert.Equal(DataValidationErrors.GetHasErrors(control), true);
+                Assert.Equal(DataValidationErrors.GetErrors(control).SequenceEqual(new[] { exception }), true);
+            });
+        }
+        
+        [Fact]
+        public void SelectedItem_Validation()
+        {
+            RunTest((control, textbox) =>
+            {
+                var exception = new InvalidCastException("failed validation");
+                var itemObservable = new BehaviorSubject<BindingNotification>(new BindingNotification(exception, BindingErrorType.DataValidationError));
+                control.Bind(AutoCompleteBox.SelectedItemProperty, itemObservable);
+                Dispatcher.UIThread.RunJobs();
+
+                Assert.Equal(DataValidationErrors.GetHasErrors(control), true);
+                Assert.Equal(DataValidationErrors.GetErrors(control).SequenceEqual(new[] { exception }), true);
+            });
+        }
 
         /// <summary>
         /// Retrieves a defined predicate filter through a new AutoCompleteBox