Fix focus when switching back to assembly list via keyboard

ILSpy/AssemblyTree/AssemblyListPane.xaml

@@ -7,6 +7,7 @@
 						xmlns:treeNodes="clr-namespace:ICSharpCode.ILSpy.TreeNodes"
 						xmlns:assemblyTree="clr-namespace:ICSharpCode.ILSpy.AssemblyTree"
 						xmlns:toms="urn:TomsToolbox"
+						xmlns:viewModels="clr-namespace:ICSharpCode.ILSpy.ViewModels"
 						mc:Ignorable="d" d:DesignHeight="450" d:DesignWidth="800"
 						d:DataContext="{d:DesignInstance assemblyTree:AssemblyTreeModel}"
 						AutomationProperties.Name="Assemblies and Classes"
@@ -15,7 +16,8 @@
 						AllowDrop="True"
 						BorderThickness="0" Visibility="Visible"
 						Root="{Binding Root}"
-						toms:MultiSelectorExtensions.SelectionBinding="{Binding SelectedItems, Mode=TwoWay}">
+						toms:MultiSelectorExtensions.SelectionBinding="{Binding SelectedItems, Mode=TwoWay}"
+						viewModels:Pane.IsActive="{Binding IsActive}">
 	<treeView:SharpTreeView.ItemContainerStyle>
 		<Style TargetType="treeView:SharpTreeViewItem">
 			<Setter Property="Template">

ILSpy/AssemblyTree/AssemblyListPane.xaml.cs

@@ -20,6 +20,9 @@ using System.ComponentModel.Composition;
 using System.Windows;
 using System.Windows.Threading;
 
+using ICSharpCode.ILSpy.ViewModels;
+using ICSharpCode.ILSpyX.TreeView;
+
 using TomsToolbox.Wpf.Composition.Mef;
 
 namespace ICSharpCode.ILSpy.AssemblyTree
@@ -59,6 +62,20 @@ namespace ICSharpCode.ILSpy.AssemblyTree
 					});
 				}
 			}
+			else if (e.Property == Pane.IsActiveProperty)
+			{
+				if (!true.Equals(e.NewValue))
+					return;
+
+				if (SelectedItem is SharpTreeNode selectedItem)
+				{
+					FocusNode(selectedItem);
+				}
+				else
+				{
+					Focus();
+				}
+			}
 		}
 	}
 }