Property changes.

src/Avalonia.Controls/Window.cs

@@ -78,9 +78,16 @@ namespace Avalonia.Controls
         public static readonly StyledProperty<WindowIcon> IconProperty =
             AvaloniaProperty.Register<Window, WindowIcon>(nameof(Icon));
 
+        /// <summary>
+        /// Defines the <see cref="WindowStartupLocation"/> proeprty.
+        /// </summary>
+        public static readonly DirectProperty<Window, WindowStartupLocation> WindowStartupLocationProperty =
+            AvaloniaProperty.RegisterDirect<Window, WindowStartupLocation>(nameof(WindowStartupLocation), o => o.WindowStartupLocation);
+
         private readonly NameScope _nameScope = new NameScope();
         private object _dialogResult;
         private readonly Size _maxPlatformClientSize;
+        private WindowStartupLocation _windowStartupLoction;
 
         /// <summary>
         /// Initializes static members of the <see cref="Window"/> class.
@@ -188,8 +195,8 @@ namespace Avalonia.Controls
         /// </summary>
         public WindowStartupLocation WindowStartupLocation
         {
-            get;
-            set;
+            get { return _windowStartupLoction; }
+            set { SetAndRaise(WindowStartupLocationProperty, ref _windowStartupLoction, value); }
         }
 
         /// <inheritdoc/>
@@ -336,6 +343,8 @@ namespace Avalonia.Controls
         {
             if (WindowStartupLocation == WindowStartupLocation.CenterScreen)
             {
+                // This should be using a Screen API, but we don't have one yet and
+                // PlatformImpl.MaxClientSize is the best we have.
                 if (PlatformImpl != null)
                 {
                     var positionAsSize = PlatformImpl.MaxClientSize / 2 - ClientSize / 2;

src/Avalonia.Controls/WindowBase.cs

@@ -32,12 +32,13 @@ namespace Avalonia.Controls
         /// <summary>
         /// Defines the <see cref="Owner"/> property.
         /// </summary>
-        public static readonly StyledProperty<WindowBase> OwnerProperty =
-            AvaloniaProperty.Register<WindowBase, WindowBase>(nameof(Owner));
+        public static readonly DirectProperty<WindowBase, WindowBase> OwnerProperty =
+            AvaloniaProperty.RegisterDirect<WindowBase, WindowBase>(nameof(Owner), o => o.Owner);
 
         private bool _hasExecutedInitialLayoutPass;
         private bool _isActive;
         private bool _ignoreVisibilityChange;
+        private WindowBase _owner;
 
         static WindowBase()
         {
@@ -111,8 +112,8 @@ namespace Avalonia.Controls
         /// </summary>
         public WindowBase Owner
         {
-            get { return GetValue(OwnerProperty); }
-            set { SetValue(OwnerProperty, value); }
+            get { return _owner; }
+            set { SetAndRaise(OwnerProperty, ref _owner, value); }
         }
 
         /// <summary>