Using the WPF FocusScope

using System;
using System.Windows;
using System.Windows.Input;
using System.Windows.Media;

namespace TestApp
{
	/// <summary>
	/// Attached behavior for improved focus scope handling.
	/// </summary>
	public static class EnhancedFocusScope
	{
		public static void SetFocusOnActiveElementInScope(UIElement scope)
		{
			IInputElement focusedElement = FocusManager.GetFocusedElement(scope);
			if (focusedElement != null) {
				Keyboard.Focus(focusedElement);
			} else {
				scope.MoveFocus(new TraversalRequest(FocusNavigationDirection.First));
			}
		}
		
		public static bool GetIsEnhancedFocusScope(UIElement element)
		{
			return (bool)element.GetValue(IsEnhancedFocusScopeProperty);
		}
		
		public static void SetIsEnhancedFocusScope(UIElement element, bool value)
		{
			element.SetValue(IsEnhancedFocusScopeProperty, value);
		}
		
		public static readonly DependencyProperty IsEnhancedFocusScopeProperty =
			DependencyProperty.RegisterAttached(
				"IsEnhancedFocusScope",
				typeof(bool),
				typeof(EnhancedFocusScope),
				new UIPropertyMetadata(false, OnIsEnhancedFocusScopeChanged));
		
		static void OnIsEnhancedFocusScopeChanged(DependencyObject depObj, DependencyPropertyChangedEventArgs e)
		{
			UIElement item = depObj as UIElement;
			if (item == null)
				return;
			
			if ((bool)e.NewValue) {
				FocusManager.SetIsFocusScope(item, true);
				item.GotKeyboardFocus += OnGotKeyboardFocus;
			} else {
				FocusManager.SetIsFocusScope(item, false);
				item.GotKeyboardFocus -= OnGotKeyboardFocus;
			}
		}
		
		static void OnGotKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
		{
			IInputElement focusedElement = e.NewFocus;
			for (DependencyObject d = focusedElement as DependencyObject; d != null; d = VisualTreeHelper.GetParent(d)) {
				if (FocusManager.GetIsFocusScope(d)) {
					d.SetValue(FocusManager.FocusedElementProperty, focusedElement);
					if (!(bool)d.GetValue(IsEnhancedFocusScopeProperty)) {
						break;
					}
				}
			}
		}
	}
}