Started to implement data validation on TextBox.

Not working still - added a failing test to demonstrate it.

src/Avalonia.Base/DirectProperty.cs

@@ -85,19 +85,26 @@ namespace Avalonia
         /// The value to use when the property is set to <see cref="AvaloniaProperty.UnsetValue"/>
         /// </param>
         /// <param name="defaultBindingMode">The default binding mode for the property.</param>
+        /// <param name="enableDataValidation">
+        /// Whether the property is interested in data validation.
+        /// </param>
         /// <returns>The property.</returns>
         public DirectProperty<TNewOwner, TValue> AddOwner<TNewOwner>(
             Func<TNewOwner, TValue> getter,
             Action<TNewOwner, TValue> setter = null,
             TValue unsetValue = default(TValue),
-            BindingMode defaultBindingMode = BindingMode.OneWay)
+            BindingMode defaultBindingMode = BindingMode.OneWay,
+            bool enableDataValidation = false)
                 where TNewOwner : AvaloniaObject
         {
             var result = new DirectProperty<TNewOwner, TValue>(
                 this,
                 getter,
                 setter,
-                new DirectPropertyMetadata<TValue>(unsetValue, defaultBindingMode));
+                new DirectPropertyMetadata<TValue>(
+                    unsetValue: unsetValue,
+                    defaultBindingMode: defaultBindingMode,
+                    enableDataValidation: enableDataValidation));
 
             AvaloniaPropertyRegistry.Instance.Register(typeof(TNewOwner), result);
             return result;

src/Avalonia.Controls/TextBox.cs

@@ -35,6 +35,9 @@ namespace Avalonia.Controls
                 o => o.CaretIndex,
                 (o, v) => o.CaretIndex = v);
 
+        public static readonly StyledProperty<bool> IsReadOnlyProperty =
+            AvaloniaProperty.Register<TextBox, bool>(nameof(IsReadOnly));
+
         public static readonly DirectProperty<TextBox, int> SelectionStartProperty =
             AvaloniaProperty.RegisterDirect<TextBox, int>(
                 nameof(SelectionStart),
@@ -51,7 +54,8 @@ namespace Avalonia.Controls
             TextBlock.TextProperty.AddOwner<TextBox>(
                 o => o.Text,
                 (o, v) => o.Text = v,
-                defaultBindingMode: BindingMode.TwoWay);
+                defaultBindingMode: BindingMode.TwoWay,
+                enableDataValidation: true);
 
         public static readonly StyledProperty<TextAlignment> TextAlignmentProperty =
             TextBlock.TextAlignmentProperty.AddOwner<TextBox>();
@@ -65,9 +69,6 @@ namespace Avalonia.Controls
         public static readonly StyledProperty<bool> UseFloatingWatermarkProperty =
             AvaloniaProperty.Register<TextBox, bool>("UseFloatingWatermark");
 
-        public static readonly StyledProperty<bool> IsReadOnlyProperty =
-            AvaloniaProperty.Register<TextBox, bool>(nameof(IsReadOnly));
-
         struct UndoRedoState : IEquatable<UndoRedoState>
         {
             public string Text { get; }
@@ -145,6 +146,12 @@ namespace Avalonia.Controls
             }
         }
 
+        public bool IsReadOnly
+        {
+            get { return GetValue(IsReadOnlyProperty); }
+            set { SetValue(IsReadOnlyProperty, value); }
+        }
+
         public int SelectionStart
         {
             get
@@ -198,12 +205,6 @@ namespace Avalonia.Controls
             set { SetValue(UseFloatingWatermarkProperty, value); }
         }
 
-        public bool IsReadOnly
-        {
-            get { return GetValue(IsReadOnlyProperty); }
-            set { SetValue(IsReadOnlyProperty, value); }
-        }
-
         public TextWrapping TextWrapping
         {
             get { return GetValue(TextWrappingProperty); }
@@ -461,6 +462,11 @@ namespace Avalonia.Controls
             }
         }
 
+        protected override void UpdateDataValidation(AvaloniaProperty property, BindingNotification status)
+        {
+            ((IPseudoClasses)Classes).Set(":error", status != null && status.ErrorType != BindingErrorType.None);
+        }
+
         private int CoerceCaretIndex(int value)
         {
             var text = Text;

tests/Avalonia.Controls.UnitTests/TextBoxTests_ValidationState.cs

@@ -5,8 +5,13 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.ComponentModel;
+using Avalonia.Controls.Presenters;
+using Avalonia.Controls.Templates;
+using Avalonia.Data;
 using Avalonia.Markup.Xaml.Data;
+using Avalonia.Platform;
 using Avalonia.UnitTests;
+using Moq;
 using Xunit;
 
 namespace Avalonia.Controls.UnitTests
@@ -14,63 +19,44 @@ namespace Avalonia.Controls.UnitTests
     public class TextBoxTests_ValidationState
     {
         [Fact]
-        public void Setter_Exceptions_Should_Set_ValidationState()
+        public void Setter_Exceptions_Should_Set_Error_Pseudoclass()
         {
-            using (UnitTestApplication.Start(TestServices.MockThreadingInterface))
+            using (UnitTestApplication.Start(Services))
             {
-                var target = new TextBox();
+                var target = new TextBox
-                var binding = new Binding(nameof(ExceptionTest.LessThan10));
+                {
-                binding.Source = new ExceptionTest();
+                    DataContext = new ExceptionTest(),
-                ////binding.EnableValidation = true;
+                    [!TextBox.TextProperty] = new Binding(nameof(ExceptionTest.LessThan10), BindingMode.TwoWay),
-                target.Bind(TextBox.TextProperty, binding);
+                    Template = CreateTemplate(),
+                };
 
-                Assert.True(false);
+                target.ApplyTemplate();
-                //Assert.True(target.ValidationStatus.IsValid);
-                //target.Text = "20";
-                //Assert.False(target.ValidationStatus.IsValid);
-                //target.Text = "1";
-                //Assert.True(target.ValidationStatus.IsValid);
-            }
-        }
 
-        [Fact(Skip = "TODO: Not yet passing")]
+                Assert.False(target.Classes.Contains(":error"));
-        public void Unconvertable_Value_Should_Set_ValidationState()
+                target.Text = "20";
-        {
+                Assert.True(target.Classes.Contains(":error"));
-            using (UnitTestApplication.Start(TestServices.MockThreadingInterface))
+                target.Text = "1";
-            {
+                Assert.False(target.Classes.Contains(":error"));
-                var target = new TextBox();
-                var binding = new Binding(nameof(ExceptionTest.LessThan10));
-                binding.Source = new ExceptionTest();
-                ////binding.EnableValidation = true;
-                target.Bind(TextBox.TextProperty, binding);
-
-                Assert.True(false);
-                //Assert.True(target.ValidationStatus.IsValid);
-                //target.Text = "foo";
-                //Assert.False(target.ValidationStatus.IsValid);
-                //target.Text = "1";
-                //Assert.True(target.ValidationStatus.IsValid);
             }
         }
 
-        [Fact]
+        private static TestServices Services => TestServices.MockThreadingInterface.With(
-        public void Indei_Should_Set_ValidationState()
+            standardCursorFactory: Mock.Of<IStandardCursorFactory>());
-        {
-            using (UnitTestApplication.Start(TestServices.MockThreadingInterface))
-            {
-                var target = new TextBox();
-                var binding = new Binding(nameof(ExceptionTest.LessThan10));
-                binding.Source = new IndeiTest();
-                ////binding.EnableValidation = true;
-                target.Bind(TextBox.TextProperty, binding);
 
-                Assert.True(false);
+        private IControlTemplate CreateTemplate()
-                //Assert.True(target.ValidationStatus.IsValid);
+        {
-                //target.Text = "20";
+            return new FuncControlTemplate<TextBox>(control =>
-                //Assert.False(target.ValidationStatus.IsValid);
+                new TextPresenter
-                //target.Text = "1";
+                {
-                //Assert.True(target.ValidationStatus.IsValid);
+                    Name = "PART_TextPresenter",
-            }
+                    [!!TextPresenter.TextProperty] = new Binding
+                    {
+                        Path = "Text",
+                        Mode = BindingMode.TwoWay,
+                        Priority = BindingPriority.TemplatedParent,
+                        RelativeSource = new RelativeSource(RelativeSourceMode.TemplatedParent),
+                    },
+                });
         }
 
         private class ExceptionTest