Simplify the TreeView.SelectedItem binding logic.

 There were many situations where the code would fail, it also accessed
 private methods.

 Automating the ScrollViewer seems much simpler than messing around with
 the ItemContainerGenerator internals.

FoxTunes.UI.Windows/Extensions/Extensions.cs

@@ -3,6 +3,7 @@
 using System.Linq;
 using System.Windows;
 using System.Windows.Controls;
+using System.Windows.Controls.Primitives;
 using System.Windows.Data;
 using System.Windows.Documents;
 using System.Windows.Interop;
@@ -312,5 +313,15 @@ public static WriteableBitmap Resize(this WriteableBitmap source, Size size)
             target.Render(visual);
             return new WriteableBitmap(target);
         }
+
+        public static void ScrollToItemOffset<T>(this ScrollViewer scrollViewer, int offset) where T : FrameworkElement
+        {
+            var item = scrollViewer.FindChild<T>();
+            if (item == null)
+            {
+                return;
+            }
+            scrollViewer.ScrollToVerticalOffset(offset * item.ActualHeight);
+        }
     }
 }

FoxTunes.UI.Windows/Extensions/TreeView_SelectedItem.cs

@@ -1,6 +1,5 @@
 using FoxTunes.Interfaces;
 using System.Collections.Generic;
-using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Windows;
 using System.Windows.Controls;
@@ -46,25 +45,6 @@ private static void OnSelectedItemPropertyChanged(DependencyObject sender, Depen
 
         private class SelectedItemBehaviour : UIBehaviour
         {
-            private static readonly PropertyInfo ItemsHost = typeof(ItemsControl).GetProperty(
-                "ItemsHost",
-                BindingFlags.Instance | BindingFlags.NonPublic
-             );
-
-            private static readonly MethodInfo EnsureGenerator = typeof(Panel).GetMethod(
-                "EnsureGenerator",
-                BindingFlags.Instance | BindingFlags.NonPublic
-            );
-
-#if NET40
-
-            private static readonly MethodInfo BringIndexIntoView = typeof(VirtualizingPanel).GetMethod(
-                "BringIndexIntoView",
-                BindingFlags.Instance | BindingFlags.NonPublic
-            );
-
-#endif
-
             public SelectedItemBehaviour(TreeView treeView)
             {
                 this.TreeView = treeView;
@@ -126,73 +106,48 @@ protected virtual void Select(Stack<IHierarchical> stack)
                     }
                     if (item != null)
                     {
-                        //If we had a previous item then expand it.
                         item.IsExpanded = true;
                         items = item;
                     }
                     else
                     {
-                        //Else it's the first iteration.
                         items = this.TreeView;
                     }
-                    //Try the easy method.
-                    item = items.ItemContainerGenerator.ContainerFromItem(value) as TreeViewItem;
+                    item = this.BringIntoView(items, value);
                     if (item == null)
                     {
-                        //Looks like the item hasn't been generated.
-                        //Apply any templates we might need.
-                        if (items.Template != null)
-                        {
-                            items.ApplyTemplate();
-                            var presenter = items.Template.FindName("ItemsHost", items) as ItemsPresenter;
-                            if (presenter != null)
-                            {
-                                presenter.ApplyTemplate();
-                            }
-                        }
-                        //Update the layout and get the panel.
-                        items.UpdateLayout();
-                        var panel = ItemsHost.GetValue(items, null) as VirtualizingPanel;
-                        if (panel != null)
-                        {
-                            //Enssure the ItemContainerGenerator is constructed.
-                            EnsureGenerator.Invoke(panel, null);
-                            //Get the index of the value.
-                            var index = items.Items.IndexOf(value);
-                            if (index < 0)
-                            {
-                                //There is no item corresponding to the current value.
-                                //Nothing can be done.
-                                break;
-                            }
-                            //Tell the panel to being the index into view.
-                            //This will create the item we're looking for.
-#if NET40
-                            BringIndexIntoView.Invoke(panel, new object[] { index });
-#else
-                            panel.BringIndexIntoViewPublic(index);
-#endif
-                        }
-                        //Try the easy method (again).
-                        item = items.ItemContainerGenerator.ContainerFromItem(value) as TreeViewItem;
-                        if (item == null)
-                        {
-                            //Looks like the item hasn't been generated.
-                            //Nothing can be done.
-                            break;
-                        }
+                        return;
                     }
                 } while (stack.Count > 0);
+                if (item != null && !item.IsSelected)
+                {
+                    item.IsSelected = true;
+                }
+            }
 
+            protected virtual TreeViewItem BringIntoView(ItemsControl items, object value)
+            {
+                var index = items.Items.IndexOf(value);
+                if (index < 0)
+                {
+                    return null;
+                }
+                var item = items.ItemContainerGenerator.ContainerFromItem(value) as TreeViewItem;
                 if (item != null)
                 {
-                    //Found the item, select it.
-                    item.IsSelected = true;
+                    item.BringIntoView();
                 }
                 else
                 {
-
+                    var scrollViewer = items.FindChild<ScrollViewer>();
+                    if (scrollViewer != null)
+                    {
+                        scrollViewer.ScrollToItemOffset<TreeViewItem>(index);
+                        items.UpdateLayout();
+                        item = items.ItemContainerGenerator.ContainerFromItem(value) as TreeViewItem;
+                    }
                 }
+                return item;
             }
 
             protected virtual void OnSelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)

FoxTunes.UI.Windows/LibraryTree.xaml

@@ -34,7 +34,6 @@
         <TreeView x:Name="TreeView" Margin="0,2,0,2"
                   ItemsSource="{Binding Items, Source={StaticResource ViewModel}, IsAsync=True}"
                   Windows:TreeViewExtensions.SelectedItem="{Binding SelectedItem, Source={StaticResource ViewModel}}"
-                  Windows:TreeViewExtensions.EnsureSelectedItemVisible="True"
                   Windows:TreeViewExtensions.RightButtonSelect="True"
                   Windows:TreeViewExtensions.DragSource="True"
                   Windows:TreeViewExtensions.DragSourceInitialized="DragSourceInitialized"