Fix focus when active tab page is changed via the Window menu

ILSpy/Commands/ShowPane.cs

@@ -1,5 +1,4 @@
 using ICSharpCode.ILSpy.Docking;
-using ICSharpCode.ILSpy.Properties;
 using ICSharpCode.ILSpy.ViewModels;
 
 namespace ICSharpCode.ILSpy.Commands
@@ -30,7 +29,13 @@ public TabPageCommand(TabPageModel model)
 
 		public override void Execute(object parameter)
 		{
-			DockWorkspace.Instance.ActiveTabPage = model;
+			var workspace = DockWorkspace.Instance;
+
+			// ensure the tab control is focused before setting the active tab page, else the tab will not be focused
+			workspace.ActiveTabPage?.Focus();
+			// reset first, else clicking on the already active tab will not focus the tab and the menu checkmark will not be updated
+			workspace.ActiveTabPage = null;
+			workspace.ActiveTabPage = model;
 		}
 	}
 }

ILSpy/Util/MenuService.cs

@@ -207,7 +207,8 @@ static Control CreateMenuItem(TabPageModel pane, DockWorkspace dock)
 			menuItem.SetBinding(MenuItem.IsCheckedProperty, new Binding(nameof(dock.ActiveTabPage)) {
 				Source = dock,
 				ConverterParameter = pane,
-				Converter = BinaryOperationConverter.Equality
+				Converter = BinaryOperationConverter.Equality,
+				Mode = BindingMode.OneWay
 			});
 
 			return menuItem;

ILSpy/ViewModels/TabPageModel.cs

@@ -17,10 +17,14 @@
 // DEALINGS IN THE SOFTWARE.
 
 using System;
+using System.Linq;
 using System.Threading.Tasks;
+using System.Windows;
 
 using ICSharpCode.ILSpy.TextView;
 
+using TomsToolbox.Wpf;
+
 namespace ICSharpCode.ILSpy.ViewModels
 {
 	public class TabPageModel : PaneModel
@@ -96,6 +100,19 @@ public static void ShowTextView(this TabPageModel tabPage, Action<DecompilerText
 			tabPage.Title = Properties.Resources.Decompiling;
 			action(textView);
 		}
+
+		public static void Focus(this TabPageModel tabPage)
+		{
+			if (tabPage.Content is not FrameworkElement content)
+				return;
+
+			var focusable = content
+				.VisualDescendantsAndSelf()
+				.OfType<FrameworkElement>()
+				.FirstOrDefault(item => item.Focusable);
+
+			focusable?.Focus();
+		}
 	}
 
 	public interface IHaveState