Merge overridden direct property metadata.

src/Avalonia.Base/DirectProperty.cs

@@ -30,7 +30,7 @@ namespace Avalonia
             string name,
             Func<TOwner, TValue> getter,
             Action<TOwner, TValue> setter,
-            PropertyMetadata metadata)
+            DirectPropertyMetadata<TValue> metadata)
             : base(name, typeof(TOwner), metadata)
         {
             Contract.Requires<ArgumentNullException>(getter != null);
@@ -50,7 +50,7 @@ namespace Avalonia
             AvaloniaProperty<TValue> source,
             Func<TOwner, TValue> getter,
             Action<TOwner, TValue> setter,
-            PropertyMetadata metadata)
+            DirectPropertyMetadata<TValue> metadata)
             : base(source, typeof(TOwner), metadata)
         {
             Contract.Requires<ArgumentNullException>(getter != null);
@@ -93,18 +93,22 @@ namespace Avalonia
             Func<TNewOwner, TValue> getter,
             Action<TNewOwner, TValue> setter = null,
             TValue unsetValue = default(TValue),
-            BindingMode defaultBindingMode = BindingMode.OneWay,
+            BindingMode defaultBindingMode = BindingMode.Default,
             bool enableDataValidation = false)
                 where TNewOwner : AvaloniaObject
         {
+            var metadata = new DirectPropertyMetadata<TValue>(
+                unsetValue: unsetValue,
+                defaultBindingMode: defaultBindingMode,
+                enableDataValidation: enableDataValidation);
+
+            metadata.Merge(GetMetadata<TOwner>(), this);
+
             var result = new DirectProperty<TNewOwner, TValue>(
                 this,
                 getter,
                 setter,
-                new DirectPropertyMetadata<TValue>(
-                    unsetValue: unsetValue,
-                    defaultBindingMode: defaultBindingMode,
-                    enableDataValidation: enableDataValidation));
+                metadata);
 
             AvaloniaPropertyRegistry.Instance.Register(typeof(TNewOwner), result);
             return result;

src/Avalonia.Base/DirectPropertyMetadata`1.cs

@@ -23,7 +23,7 @@ namespace Avalonia
         public DirectPropertyMetadata(
             TValue unsetValue = default(TValue),
             BindingMode defaultBindingMode = BindingMode.Default,
-            bool enableDataValidation = false)
+            bool? enableDataValidation = null)
                 : base(defaultBindingMode)
         {
             UnsetValue = unsetValue;
@@ -44,7 +44,7 @@ namespace Avalonia
         /// control (such as a TextBox's Text property) will be interested in recieving data
         /// validation messages so this feature must be explicitly enabled by setting this flag.
         /// </remarks>
-        public bool EnableDataValidation { get; }
+        public bool? EnableDataValidation { get; private set; }
 
         /// <inheritdoc/>
         object IDirectPropertyMetadata.UnsetValue => UnsetValue;
@@ -62,6 +62,11 @@ namespace Avalonia
                 {
                     UnsetValue = src.UnsetValue;
                 }
+
+                if (EnableDataValidation == null)
+                {
+                    EnableDataValidation = src.EnableDataValidation;
+                }
             }
         }
     }

src/Avalonia.Base/IDirectPropertyMetadata.cs

@@ -16,6 +16,6 @@ namespace Avalonia
         /// <summary>
         /// Gets a value indicating whether the property is interested in data validation.
         /// </summary>
-        bool EnableDataValidation { get; }
+        bool? EnableDataValidation { get; }
     }
 }

tests/Avalonia.Base.UnitTests/AvaloniaObjectTests_Direct.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Reactive.Subjects;
+using Avalonia;
 using Avalonia.Data;
 using Avalonia.Logging;
 using Avalonia.UnitTests;
@@ -410,6 +411,34 @@ namespace Avalonia.Base.UnitTests
             Assert.True(called);
         }
 
+        [Fact]
+        public void AddOwner_Should_Inherit_DefaultBindingMode()
+        {
+            var foo = new DirectProperty<Class1, string>(
+                "foo",
+                o => "foo",
+                null,
+                new DirectPropertyMetadata<string>(defaultBindingMode: BindingMode.TwoWay));
+            var bar = foo.AddOwner<Class2>(o => "bar");
+
+            Assert.Equal(BindingMode.TwoWay, bar.GetMetadata<Class1>().DefaultBindingMode);
+            Assert.Equal(BindingMode.TwoWay, bar.GetMetadata<Class2>().DefaultBindingMode);
+        }
+
+        [Fact]
+        public void AddOwner_Can_Override_DefaultBindingMode()
+        {
+            var foo = new DirectProperty<Class1, string>(
+                "foo",
+                o => "foo",
+                null,
+                new DirectPropertyMetadata<string>(defaultBindingMode: BindingMode.TwoWay));
+            var bar = foo.AddOwner<Class2>(o => "bar", defaultBindingMode: BindingMode.OneWayToSource);
+
+            Assert.Equal(BindingMode.TwoWay, bar.GetMetadata<Class1>().DefaultBindingMode);
+            Assert.Equal(BindingMode.OneWayToSource, bar.GetMetadata<Class2>().DefaultBindingMode);
+        }
+
         private class Class1 : AvaloniaObject
         {
             public static readonly DirectProperty<Class1, string> FooProperty =

tests/Avalonia.Base.UnitTests/DirectPropertyTests.cs

@@ -34,7 +34,7 @@ namespace Avalonia.Base.UnitTests
                 "test", 
                 o => null, 
                 null, 
-                new PropertyMetadata());
+                new DirectPropertyMetadata<string>());
 
             Assert.True(target.IsDirect);
         }