Pass EnableDataValidation to ExpressionObserver.

src/Avalonia.Base/AvaloniaObjectExtensions.cs

@@ -216,7 +216,11 @@ namespace Avalonia
             Contract.Requires<ArgumentNullException>(property != null);
             Contract.Requires<ArgumentNullException>(binding != null);
 
-            var result = binding.Initiate(target, property, anchor);
+            var result = binding.Initiate(
+                target,
+                property,
+                anchor, 
+                property.GetMetadata(target.GetType()).EnabledDataValidation);
 
             if (result != null)
             {
@@ -311,7 +315,8 @@ namespace Avalonia
             public InstancedBinding Initiate(
                 IAvaloniaObject target,
                 AvaloniaProperty targetProperty,
-                object anchor = null)
+                object anchor = null,
+                bool enableDataValidation = false)
             {
                 return new InstancedBinding(_source);
             }

src/Avalonia.Base/AvaloniaProperty.cs

@@ -275,7 +275,8 @@ namespace Avalonia
             var metadata = new StyledPropertyMetadata<TValue>(
                 defaultValue,
                 validate: Cast(validate),
-                defaultBindingMode: defaultBindingMode);
+                defaultBindingMode: defaultBindingMode,
+                enableDataValidation: enableDataValidation);
 
             var result = new StyledProperty<TValue>(
                 name,
@@ -316,7 +317,8 @@ namespace Avalonia
             var metadata = new StyledPropertyMetadata<TValue>(
                 defaultValue,
                 validate: Cast(validate),
-                defaultBindingMode: defaultBindingMode);
+                defaultBindingMode: defaultBindingMode,
+                enableDataValidation: enableDataValidation);
 
             var result = new AttachedProperty<TValue>(name, typeof(TOwner), metadata, inherits);
             AvaloniaPropertyRegistry.Instance.Register(typeof(THost), result);
@@ -353,7 +355,8 @@ namespace Avalonia
             var metadata = new StyledPropertyMetadata<TValue>(
                 defaultValue,
                 validate: Cast(validate),
-                defaultBindingMode: defaultBindingMode);
+                defaultBindingMode: defaultBindingMode,
+                enableDataValidation: enableDataValidation);
 
             var result = new AttachedProperty<TValue>(name, ownerType, metadata, inherits);
             AvaloniaPropertyRegistry.Instance.Register(typeof(THost), result);
@@ -389,7 +392,8 @@ namespace Avalonia
 
             var metadata = new DirectPropertyMetadata<TValue>(
                 unsetValue: unsetValue,
-                defaultBindingMode: defaultBindingMode);
+                defaultBindingMode: defaultBindingMode,
+                enableDataValidation: enableDataValidation);
 
             var result = new DirectProperty<TOwner, TValue>(name, getter, setter, metadata);
             AvaloniaPropertyRegistry.Instance.Register(typeof(TOwner), result);

src/Avalonia.Base/Data/IBinding.cs

@@ -19,12 +19,14 @@ namespace Avalonia.Data
         /// order to locate named controls or resources. The <paramref name="anchor"/> parameter 
         /// can be used to provice this context.
         /// </param>
+        /// <param name="enableDataValidation">Whether data validation should be enabled.</param>
         /// <returns>
         /// A <see cref="InstancedBinding"/> or null if the binding could not be resolved.
         /// </returns>
         InstancedBinding Initiate(
             IAvaloniaObject target, 
             AvaloniaProperty targetProperty,
-            object anchor = null);
+            object anchor = null,
+            bool enableDataValidation = false);
     }
 }

src/Avalonia.Base/Data/IndexerBinding.cs

@@ -21,7 +21,11 @@ namespace Avalonia.Data
         public AvaloniaProperty Property { get; }
         private BindingMode Mode { get; }
 
-        public InstancedBinding Initiate(IAvaloniaObject target, AvaloniaProperty targetProperty, object anchor = null)
+        public InstancedBinding Initiate(
+            IAvaloniaObject target,
+            AvaloniaProperty targetProperty,
+            object anchor = null,
+            bool enableDataValidation = false)
         {
             var mode = Mode == BindingMode.Default ?
                 targetProperty.GetMetadata(target.GetType()).DefaultBindingMode :

src/Markup/Avalonia.Markup.Xaml/Data/Binding.cs

@@ -78,16 +78,12 @@ namespace Avalonia.Markup.Xaml.Data
         /// </summary>
         public object Source { get; set; }
 
-        /// <summary>
-        /// Gets or sets a value indicating whether the property should be validated.
-        /// </summary>
-        public bool EnableValidation { get; set; }
-
         /// <inheritdoc/>
         public InstancedBinding Initiate(
             IAvaloniaObject target,
             AvaloniaProperty targetProperty,
-            object anchor = null)
+            object anchor = null,
+            bool enableDataValidation = false)
         {
             Contract.Requires<ArgumentNullException>(target != null);
 
@@ -105,7 +101,7 @@ namespace Avalonia.Markup.Xaml.Data
             }
             else if (Source != null)
             {
-                observer = CreateSourceObserver(Source, pathInfo.Path);
+                observer = CreateSourceObserver(Source, pathInfo.Path, enableDataValidation);
             }
             else if (RelativeSource == null || RelativeSource.Mode == RelativeSourceMode.DataContext)
             {
@@ -113,7 +109,8 @@ namespace Avalonia.Markup.Xaml.Data
                     target,
                     pathInfo.Path,
                     targetProperty == Control.DataContextProperty,
-                    anchor);
+                    anchor,
+                    enableDataValidation);
             }
             else if (RelativeSource.Mode == RelativeSourceMode.TemplatedParent)
             {
@@ -197,7 +194,8 @@ namespace Avalonia.Markup.Xaml.Data
             IAvaloniaObject target,
             string path,
             bool targetIsDataContext,
-            object anchor)
+            object anchor,
+            bool enableDataValidation)
         {
             Contract.Requires<ArgumentNullException>(target != null);
 
@@ -220,7 +218,7 @@ namespace Avalonia.Markup.Xaml.Data
                     () => target.GetValue(Control.DataContextProperty),
                     path,
                     update,
-                    EnableValidation);
+                    enableDataValidation);
 
                 return result;
             }
@@ -229,7 +227,7 @@ namespace Avalonia.Markup.Xaml.Data
                 return new ExpressionObserver(
                     GetParentDataContext(target),
                     path,
-                    EnableValidation);
+                    enableDataValidation);
             }
         }
 
@@ -240,15 +238,18 @@ namespace Avalonia.Markup.Xaml.Data
             var result = new ExpressionObserver(
                 ControlLocator.Track(target, elementName),
                 path,
-                EnableValidation);
+                false);
             return result;
         }
 
-        private ExpressionObserver CreateSourceObserver(object source, string path)
+        private ExpressionObserver CreateSourceObserver(
+            object source,
+            string path,
+            bool enabledDataValidation)
         {
             Contract.Requires<ArgumentNullException>(source != null);
 
-            return new ExpressionObserver(source, path, EnableValidation);
+            return new ExpressionObserver(source, path, enabledDataValidation);
         }
 
         private ExpressionObserver CreateTemplatedParentObserver(

src/Markup/Avalonia.Markup.Xaml/Data/MultiBinding.cs

@@ -53,7 +53,8 @@ namespace Avalonia.Markup.Xaml.Data
         public InstancedBinding Initiate(
             IAvaloniaObject target,
             AvaloniaProperty targetProperty,
-            object anchor = null)
+            object anchor = null,
+            bool enableDataValidation = false)
         {
             if (Converter == null)
             {

src/Markup/Avalonia.Markup.Xaml/Data/StyleResourceBinding.cs

@@ -37,7 +37,8 @@ namespace Avalonia.Markup.Xaml.Data
         public InstancedBinding Initiate(
             IAvaloniaObject target,
             AvaloniaProperty targetProperty,
-            object anchor = null)
+            object anchor = null,
+            bool enableDataValidation = false)
         {
             if (Name == "Red")
             {

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/BindingExtension.cs

@@ -29,7 +29,6 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
                 Mode = Mode,
                 Path = Path,
                 Priority = Priority,
-                EnableValidation = EnableValidation,
             };
         }
 
@@ -41,6 +40,5 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
         public string Path { get; set; }
         public BindingPriority Priority { get; set; } = BindingPriority.LocalValue;
         public object Source { get; set; }
-        public bool EnableValidation { get; set; }
     }
 }

tests/Avalonia.Controls.UnitTests/TextBoxTests_ValidationState.cs

@@ -21,7 +21,7 @@ namespace Avalonia.Controls.UnitTests
                 var target = new TextBox();
                 var binding = new Binding(nameof(ExceptionTest.LessThan10));
                 binding.Source = new ExceptionTest();
-                binding.EnableValidation = true;
+                ////binding.EnableValidation = true;
                 target.Bind(TextBox.TextProperty, binding);
 
                 Assert.True(false);
@@ -41,7 +41,7 @@ namespace Avalonia.Controls.UnitTests
                 var target = new TextBox();
                 var binding = new Binding(nameof(ExceptionTest.LessThan10));
                 binding.Source = new ExceptionTest();
-                binding.EnableValidation = true;
+                ////binding.EnableValidation = true;
                 target.Bind(TextBox.TextProperty, binding);
 
                 Assert.True(false);
@@ -61,7 +61,7 @@ namespace Avalonia.Controls.UnitTests
                 var target = new TextBox();
                 var binding = new Binding(nameof(ExceptionTest.LessThan10));
                 binding.Source = new IndeiTest();
-                binding.EnableValidation = true;
+                ////binding.EnableValidation = true;
                 target.Bind(TextBox.TextProperty, binding);
 
                 Assert.True(false);

tests/Avalonia.Markup.Xaml.UnitTests/Data/BindingTests_Validation.cs

@@ -25,15 +25,15 @@ namespace Avalonia.Markup.Xaml.UnitTests.Data
         }
 
         [Fact]
-        public void Validated_Property_Does_Not_Receive_BindingNotifications()
+        public void Validated_Property_Receives_BindingNotifications()
         {
             var source = new ValidationTestModel { MustBePositive = 5 };
             var target = new TestControl
             {
                 DataContext = source,
-                [!TestControl.ValidatedProperty] = new Binding(nameof(source.MustBePositive)),
             };
 
+            target.Bind(TestControl.ValidatedProperty, new Binding(nameof(source.MustBePositive)));
             source.MustBePositive = 6;
 
             Assert.Equal(

tests/Avalonia.Styling.UnitTests/SetterTests.cs

@@ -27,7 +27,7 @@ namespace Avalonia.Styling.UnitTests
             var control = new TextBlock();
             var subject = new BehaviorSubject<object>("foo");
             var descriptor = new InstancedBinding(subject);
-            var binding = Mock.Of<IBinding>(x => x.Initiate(control, TextBlock.TextProperty, null) == descriptor);
+            var binding = Mock.Of<IBinding>(x => x.Initiate(control, TextBlock.TextProperty, null, false) == descriptor);
             var style = Mock.Of<IStyle>();
             var setter = new Setter(TextBlock.TextProperty, binding);