ForwardFocusBehavior

    public class ForwardFocusBehavior
    : System.Windows.Interactivity.Behavior<FrameworkElement>
    {

        private FrameworkElement ForwardTo = null;

        protected override void OnAttached()
        {
            base.OnAttached();
            this.ForwardTo = (FrameworkElement)Find(
                AssociatedObject,
                d => d.GetType() == ForwardToChildOfType);
            this.ForwardFrom.GotKeyboardFocus += AssociatedObject_GotKeyboardFocus;
        }

        protected override void OnDetaching()
        {
            base.OnDetaching();
            this.ForwardFrom.GotKeyboardFocus -= AssociatedObject_GotKeyboardFocus;
            this.ForwardTo = null;
        }

        void AssociatedObject_GotKeyboardFocus(object sender, System.Windows.Input.KeyboardFocusChangedEventArgs e)
        {
            if (null == ForwardTo)
            {
                this.ForwardTo = (FrameworkElement)Find(
                    AssociatedObject,
                    d => d.GetType() == ForwardToChildOfType);
            }

            // Detect a reverse traversal request.
            if (e.OldFocus == ForwardTo
        && e.NewFocus == ForwardFrom
        && e.KeyboardDevice.IsKeyDown(Key.Tab))
            {
                this.ForwardFrom.MoveFocus(
            new TraversalRequest(FocusNavigationDirection.Previous));
            }
            else if (this.ForwardFrom.IsKeyboardFocused)
            {
                this.ForwardTo.Focus();
            }
        }


        public FrameworkElement ForwardFrom
        {
            get { return (FrameworkElement)GetValue(ForwardFromProperty); }
            set { SetValue(ForwardFromProperty, value); }
        }

        public static readonly DependencyProperty ForwardFromProperty =
            DependencyProperty.Register("ForwardFrom", typeof(FrameworkElement),
            typeof(ForwardFocusBehavior), new UIPropertyMetadata(null));

        public Type ForwardToChildOfType
        {
            get { return (Type)GetValue(ForwardToChildOfTypeProperty); }
            set { SetValue(ForwardToChildOfTypeProperty, value); }
        }

        public static readonly DependencyProperty ForwardToChildOfTypeProperty =
            DependencyProperty.Register("ForwardToChildOfType", typeof(Type),
            typeof(ForwardFocusBehavior), new UIPropertyMetadata(null));





        /// <summary>
        /// Searches for a child element of a DependencyObject that
    /// matches the lambda condition given.
        /// </summary>
        /// <param name="obj"></param>
        /// <param name="name"></param>
        private static DependencyObject Find(DependencyObject obj, Func<DependencyObject, bool> condition)
        {
            if ((obj == null))
                return null;

            if (condition(obj))
                return obj;

            DependencyObject result = null;
            for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
            {
                result = Find(VisualTreeHelper.GetChild(obj, i), condition);

                if (null != result)
                    return result;
            }

            return null;
        }
    }