Allow for using ScrollViewer.AllowAutoHide as an attached property.

src/Avalonia.Base/AvaloniaObjectExtensions.cs

@@ -585,6 +585,30 @@ namespace Avalonia
             });
         }
 
+        /// <summary>
+        /// Subscribes to a property changed notifications for changes that originate from a
+        /// <typeparamref name="TTarget"/>.
+        /// </summary>
+        /// <typeparam name="TTarget">The type of the property change sender.</typeparam>
+        /// /// <typeparam name="TValue">The type of the property..</typeparam>
+        /// <param name="observable">The property changed observable.</param>
+        /// <param name="action">
+        /// The method to call. The parameters are the sender and the event args.
+        /// </param>
+        /// <returns>A disposable that can be used to terminate the subscription.</returns>
+        public static IDisposable AddClassHandler<TTarget, TValue>(
+            this IObservable<AvaloniaPropertyChangedEventArgs<TValue>> observable,
+            Action<TTarget, AvaloniaPropertyChangedEventArgs<TValue>> action) where TTarget : AvaloniaObject
+        {
+            return observable.Subscribe(e =>
+            {
+                if (e.Sender is TTarget target)
+                {
+                    action(target, e);
+                }
+            });
+        }
+
         /// <summary>
         /// Subscribes to a property changed notifications for changes that originate from a
         /// <typeparamref name="TTarget"/>.

src/Avalonia.Controls/ScrollViewer.cs

@@ -176,8 +176,10 @@ namespace Avalonia.Controls
         /// <summary>
         /// Defines the <see cref="AllowAutoHide"/> property.
         /// </summary>
-        public static readonly StyledProperty<bool> AllowAutoHideProperty =
+        public static readonly AttachedProperty<bool> AllowAutoHideProperty =
-            ScrollBar.AllowAutoHideProperty.AddOwner<ScrollViewer>();
+            AvaloniaProperty.RegisterAttached<ScrollViewer, Control, bool>(
+                nameof(AllowAutoHide),
+                true);
 
         /// <summary>
         /// Defines the <see cref="ScrollChanged"/> event.
@@ -207,8 +209,8 @@ namespace Avalonia.Controls
         /// </summary>
         static ScrollViewer()
         {
-            HorizontalScrollBarVisibilityProperty.Changed.AddClassHandler<ScrollViewer>((x, e) => x.ScrollBarVisibilityChanged(e));
+            HorizontalScrollBarVisibilityProperty.Changed.AddClassHandler<ScrollViewer, ScrollBarVisibility>((x, e) => x.ScrollBarVisibilityChanged(e));
-            VerticalScrollBarVisibilityProperty.Changed.AddClassHandler<ScrollViewer>((x, e) => x.ScrollBarVisibilityChanged(e));
+            VerticalScrollBarVisibilityProperty.Changed.AddClassHandler<ScrollViewer, ScrollBarVisibility>((x, e) => x.ScrollBarVisibilityChanged(e));
         }
 
         /// <summary>
@@ -526,6 +528,26 @@ namespace Avalonia.Controls
             return control.GetValue(VerticalScrollBarVisibilityProperty);
         }
 
+        /// <summary>
+        /// Gets the value of the AllowAutoHideProperty attached property.
+        /// </summary>
+        /// <param name="control">The control to set the value on.</param>
+        /// <param name="value">The value of the property.</param>
+        public static void SetAllowAutoHide(Control control, bool value)
+        {
+            control.SetValue(AllowAutoHideProperty, value);
+        }
+
+        /// <summary>
+        /// Gets the value of the AllowAutoHideProperty attached property.
+        /// </summary>
+        /// <param name="control">The control to read the value from.</param>
+        /// <returns>The value of the property.</returns>
+        public static bool GetAllowAutoHide(Control control)
+        {
+            return control.GetValue(AllowAutoHideProperty);
+        }
+
         /// <summary>
         /// Gets the value of the VerticalScrollBarVisibility attached property.
         /// </summary>
@@ -604,10 +626,10 @@ namespace Avalonia.Controls
             CalculatedPropertiesChanged();
         }
 
-        private void ScrollBarVisibilityChanged(AvaloniaPropertyChangedEventArgs e)
+        private void ScrollBarVisibilityChanged(AvaloniaPropertyChangedEventArgs<ScrollBarVisibility> e)
         {
-            var wasEnabled = !ScrollBarVisibility.Disabled.Equals(e.OldValue);
+            var wasEnabled = e.OldValue.GetValueOrDefault() != ScrollBarVisibility.Disabled;
-            var isEnabled = !ScrollBarVisibility.Disabled.Equals(e.NewValue);
+            var isEnabled = e.NewValue.GetValueOrDefault() != ScrollBarVisibility.Disabled;
 
             if (wasEnabled != isEnabled)
             {

src/Avalonia.Themes.Default/ListBox.xaml

@@ -13,7 +13,8 @@
         <ScrollViewer Name="PART_ScrollViewer"
                       Background="{TemplateBinding Background}"
                       HorizontalScrollBarVisibility="{TemplateBinding (ScrollViewer.HorizontalScrollBarVisibility)}"
-                      VerticalScrollBarVisibility="{TemplateBinding (ScrollViewer.VerticalScrollBarVisibility)}">
+                      VerticalScrollBarVisibility="{TemplateBinding (ScrollViewer.VerticalScrollBarVisibility)}"
+                      AllowAutoHide="{TemplateBinding (ScrollViewer.AllowAutoHide)}">
           <ItemsPresenter Name="PART_ItemsPresenter"
                           Items="{TemplateBinding Items}"
                           ItemsPanel="{TemplateBinding ItemsPanel}"

src/Avalonia.Themes.Default/TextBox.xaml

@@ -57,7 +57,8 @@
                 <ContentPresenter Grid.Column="0" Grid.ColumnSpan="1" Content="{TemplateBinding InnerLeftContent}"/>
                 <ScrollViewer Grid.Column="1" Grid.ColumnSpan="1"
                               HorizontalScrollBarVisibility="{TemplateBinding (ScrollViewer.HorizontalScrollBarVisibility)}"
-                              VerticalScrollBarVisibility="{TemplateBinding (ScrollViewer.VerticalScrollBarVisibility)}">
+                              VerticalScrollBarVisibility="{TemplateBinding (ScrollViewer.VerticalScrollBarVisibility)}"
+                              AllowAutoHide="{TemplateBinding (ScrollViewer.AllowAutoHide)}">
                   <Panel>
                     <TextBlock Name="watermark"
                               Opacity="0.5"

src/Avalonia.Themes.Default/TreeView.xaml

@@ -11,7 +11,8 @@
               BorderThickness="{TemplateBinding BorderThickness}">
         <ScrollViewer Background="{TemplateBinding Background}"
                       HorizontalScrollBarVisibility="{TemplateBinding (ScrollViewer.HorizontalScrollBarVisibility)}"
-                      VerticalScrollBarVisibility="{TemplateBinding (ScrollViewer.VerticalScrollBarVisibility)}">
+                      VerticalScrollBarVisibility="{TemplateBinding (ScrollViewer.VerticalScrollBarVisibility)}"
+                      AllowAutoHide="{TemplateBinding (ScrollViewer.AllowAutoHide)}">
           <ItemsPresenter Name="PART_ItemsPresenter"
                           Items="{TemplateBinding Items}"
                           ItemsPanel="{TemplateBinding ItemsPanel}"

src/Avalonia.Themes.Fluent/Controls/ListBox.xaml

@@ -24,7 +24,8 @@
           <ScrollViewer Name="PART_ScrollViewer"
                         Background="{TemplateBinding Background}"
                         HorizontalScrollBarVisibility="{TemplateBinding (ScrollViewer.HorizontalScrollBarVisibility)}"
-                        VerticalScrollBarVisibility="{TemplateBinding (ScrollViewer.VerticalScrollBarVisibility)}">
+                        VerticalScrollBarVisibility="{TemplateBinding (ScrollViewer.VerticalScrollBarVisibility)}"
+                        AllowAutoHide="{TemplateBinding (ScrollViewer.AllowAutoHide)}">
             <ItemsPresenter Name="PART_ItemsPresenter"
                             Items="{TemplateBinding Items}"
                             ItemsPanel="{TemplateBinding ItemsPanel}"

src/Avalonia.Themes.Fluent/Controls/TextBox.xaml

@@ -65,7 +65,8 @@
                              Text="{TemplateBinding Watermark}"
                              DockPanel.Dock="Top" />
                   <ScrollViewer HorizontalScrollBarVisibility="{TemplateBinding (ScrollViewer.HorizontalScrollBarVisibility)}"
-                                VerticalScrollBarVisibility="{TemplateBinding (ScrollViewer.VerticalScrollBarVisibility)}">
+                                VerticalScrollBarVisibility="{TemplateBinding (ScrollViewer.VerticalScrollBarVisibility)}"
+                                AllowAutoHide="{TemplateBinding (ScrollViewer.AllowAutoHide)}">
                       <Panel>
                         <TextBlock Name="PART_Watermark"
                                 Opacity="0.5"

src/Avalonia.Themes.Fluent/Controls/TreeView.xaml

@@ -12,7 +12,8 @@
               BorderThickness="{TemplateBinding BorderThickness}">
         <ScrollViewer Background="{TemplateBinding Background}"
                       HorizontalScrollBarVisibility="{TemplateBinding (ScrollViewer.HorizontalScrollBarVisibility)}"
-                      VerticalScrollBarVisibility="{TemplateBinding (ScrollViewer.VerticalScrollBarVisibility)}">
+                      VerticalScrollBarVisibility="{TemplateBinding (ScrollViewer.VerticalScrollBarVisibility)}"
+                      AllowAutoHide="{TemplateBinding (ScrollViewer.AllowAutoHide)}">
           <ItemsPresenter Name="PART_ItemsPresenter"
                           Items="{TemplateBinding Items}"
                           ItemsPanel="{TemplateBinding ItemsPanel}"