Fix ScrollBar.Value.

Wasn't being updated inside ListBox and this is why...

Perspex.Controls/Primitives/ScrollBar.cs

@@ -9,6 +9,7 @@ namespace Perspex.Controls.Primitives
     using System;
     using System.Reactive;
     using System.Reactive.Linq;
+    using Perspex.Controls.Templates;
 
     public class ScrollBar : TemplatedControl
     {
@@ -88,6 +89,18 @@ namespace Perspex.Controls.Primitives
             return base.MeasureOverride(availableSize);
         }
 
+        protected override void OnTemplateApplied()
+        {
+            base.OnTemplateApplied();
+
+            // Binding between this.Value and track.Value must be done explicitly like this rather 
+            // than using standard bindings as it shouldn't be able to to be overridden by binding
+            // e.g. ScrollBar.Value.
+            var track = this.GetTemplateChild<Track>("track");
+            track.GetObservable(ValueProperty).Subscribe(x => this.Value = x);
+            this.GetObservable(ValueProperty).Subscribe(x => track.Value = x);
+        }
+
         private bool CalculateIsVisible()
         {
             switch (this.Visibility)

Perspex.Themes.Default/ScrollBarStyle.cs

@@ -66,9 +66,9 @@ namespace Perspex.Themes.Default
                 Background = Brushes.Silver,
                 Content = new Track
                 {
+                    Id = "track",
                     [~Track.MinimumProperty] = control[~ScrollBar.MinimumProperty],
                     [~Track.MaximumProperty] = control[~ScrollBar.MaximumProperty],
-                    [~~Track.ValueProperty] = control[~ScrollBar.ValueProperty],
                     [~Track.ViewportSizeProperty] = control[~ScrollBar.ViewportSizeProperty],
                     [~Track.OrientationProperty] = control[~ScrollBar.OrientationProperty],
                     Thumb = new Thumb

Perspex.Themes.Default/ScrollViewerStyle.cs

@@ -31,7 +31,9 @@ namespace Perspex.Themes.Default
 
         private Control Template(ScrollViewer control)
         {
-            return new Grid
+            ScrollBar vert;
+
+            var result = new Grid
             {
                 ColumnDefinitions = new ColumnDefinitions
                 {
@@ -59,23 +61,27 @@ namespace Perspex.Themes.Default
                         Id = "horizontalScrollBar",
                         Orientation = Orientation.Horizontal,
                         [~ScrollBar.MaximumProperty] = control[~ScrollViewer.HorizontalScrollBarMaximumProperty],
-                        [~~ScrollBar.ValueProperty] = control[~~ScrollViewer.HorizontalScrollBarValueProperty],
+                        //[~~ScrollBar.ValueProperty] = control[~~ScrollViewer.HorizontalScrollBarValueProperty],
                         [~ScrollBar.ViewportSizeProperty] = control[~ScrollViewer.HorizontalScrollBarViewportSizeProperty],
                         [~ScrollBar.VisibilityProperty] = control[~ScrollViewer.HorizontalScrollBarVisibilityProperty],
                         [Grid.RowProperty] = 1,
                     },
-                    new ScrollBar
+                    (vert = new ScrollBar
                     {
                         Id = "verticalScrollBar",
                         Orientation = Orientation.Vertical,
                         [~ScrollBar.MaximumProperty] = control[~ScrollViewer.VerticalScrollBarMaximumProperty],
-                        [~~ScrollBar.ValueProperty] = control[~~ScrollViewer.VerticalScrollBarValueProperty],
+                        //[~~ScrollBar.ValueProperty] = control[~~ScrollViewer.VerticalScrollBarValueProperty],
                         [~ScrollBar.ViewportSizeProperty] = control[~ScrollViewer.VerticalScrollBarViewportSizeProperty],
                         [~ScrollBar.VisibilityProperty] = control[~ScrollViewer.VerticalScrollBarVisibilityProperty],
                         [Grid.ColumnProperty] = 1,
-                    },
+                    }),
                 },
             };
+
+            vert[~~ScrollBar.ValueProperty] = control[~~ScrollViewer.VerticalScrollBarValueProperty];
+
+            return result;
         }
     }
 }