KeyboardTabBehavior to work with Telerik TextBox and PasswordBox

KeyboardTabBehavior.cs

public class KeyboardTabBehavior : Behavior<UIElement>
	{
		private KeyboardTabHelper _keyboardTabHelper;

		protected override void OnAttached()
		{
			base.OnAttached();
			_keyboardTabHelper = new KeyboardTabHelper(AssociatedObject);
		}

		protected override void OnDetaching()
		{
			base.OnDetaching();
			_keyboardTabHelper.OnDetach();
		}
	}

KeyboardTabHelper.cs

public class KeyboardTabHelper
	{
		private readonly UIElement _associatedObject;
		private readonly PhoneApplicationPage _phoneApplicationPage;
		private List<TabControl> _tabControls;
		private TabControl _lastTabControl;

		public KeyboardTabHelper(UIElement associatedObject)
		{
			_associatedObject = associatedObject;

			_phoneApplicationPage =
				((PhoneApplicationFrame) Application.Current.RootVisual).Content as PhoneApplicationPage;
			if (_phoneApplicationPage == null)
				throw new NullReferenceException("_phoneApplicationPage");

			_phoneApplicationPage.Loaded += OnPhoneApplicationPageOnLoaded;
			_associatedObject.KeyDown += OnAssociatedObjectKeyDown;
		}

		public void OnDetach()
		{
			UnRegisterTabControlEvents(_tabControls);
			_associatedObject.KeyDown -= OnAssociatedObjectKeyDown;
			_phoneApplicationPage.Loaded -= OnPhoneApplicationPageOnLoaded;
		}

		private void OnPhoneApplicationPageOnLoaded(object sender, RoutedEventArgs args)
		{
			FindTabControls((UIElement) sender);
		}

		private void FindTabControls(UIElement layoutRoot)
		{
			_tabControls = GetChildren(layoutRoot).OfType<Control>()
				.Where(c => c.IsTabStop && c.TabIndex != int.MaxValue)
				.OrderBy(c => c.TabIndex)
				.Select(c => new TabControl {Control = c, KeyboardFocusedControl = null})
				.ToList();

			RegisterTabControlEvents(_tabControls);

			if (_tabControls.Count > 0)
				_lastTabControl = _tabControls[_tabControls.Count - 1];
		}

		private void RegisterTabControlEvents(IEnumerable<TabControl> tabControls)
		{
			tabControls.Apply(tabControl => { tabControl.Control.GotFocus += OnTabbedControlGotFocus; });
		}

		private void UnRegisterTabControlEvents(IEnumerable<TabControl> tabbedControls)
		{
			tabbedControls.Apply(tabControl => { tabControl.Control.GotFocus -= OnTabbedControlGotFocus; });
		}

		private void OnTabbedControlGotFocus(object sender, RoutedEventArgs e)
		{
			var tabControlWithFocus = _tabControls.FirstOrDefault(t => t.Control == sender);
			if (tabControlWithFocus == null)
				return;

			tabControlWithFocus.KeyboardFocusedControl = e.OriginalSource as Control;
		}

		private void OnAssociatedObjectKeyDown(object sender, KeyEventArgs e)
		{
			if (e.Key == Key.Enter)
				HandleReturnKey();
		}

		private void HandleReturnKey()
		{
			var controlWithFocus = FocusManager.GetFocusedElement() as Control;
			if (controlWithFocus == null)
				return;

			var tabCcontrolWithFocus = FindTabControlWithFocus(controlWithFocus);
			if (tabCcontrolWithFocus == null)
				return;

			SetFocusOnNextControl(tabCcontrolWithFocus);
		}

		private TabControl FindTabControlWithFocus(Control controlWithFocus)
		{
			return _tabControls.FirstOrDefault(tabControl => tabControl.Control == controlWithFocus
			                                                 || tabControl.KeyboardFocusedControl == controlWithFocus);
		}

		private void SetFocusOnNextControl(TabControl tabControl)
		{
			if (_lastTabControl.KeyboardFocusedControl == tabControl.KeyboardFocusedControl)
				_phoneApplicationPage.Focus();
			else
			{
				var nextControl = _tabControls
					.FirstOrDefault(c => c.Control.TabIndex > tabControl.Control.TabIndex);
				var wasFocusSet = false;
				if (nextControl != null)
					wasFocusSet = nextControl.Control.Focus();

				if (!wasFocusSet)
					SetFocusOnNextControl(nextControl);
			}
		}

		private static IEnumerable<DependencyObject> GetChildren(DependencyObject root)
		{
			var children = new List<DependencyObject> {root};
			for (var i = 0; i < VisualTreeHelper.GetChildrenCount(root); i++)
				children.AddRange(GetChildren(VisualTreeHelper.GetChild(root, i)));

			return children;
		}

		private class TabControl
		{
			public Control Control { get; set; }
			public Control KeyboardFocusedControl { get; set; }
		}
	}