Microsoft.Windows.Controls.Ribbon.RibbonMenuButton.OnNavigationKeyDown C# (CSharp) Метод

        internal void OnNavigationKeyDown(KeyEventArgs e)
        {
            int focusedIndex = ItemContainerGenerator.IndexFromContainer(e.OriginalSource as DependencyObject);
            bool itemNavigateFromCurrentFocused = true;
            if (focusedIndex < 0)
            {
                UIElement popupChild = _popup.TryGetChild();
                if (popupChild != null &&
                    popupChild.IsKeyboardFocusWithin)
                {
                    // If the popup already has focus within,
                    // then the focused element is not the item container
                    // itself, but is inside one such container (eg. filter button
                    // of gallery). Hence do not navigate in such case, but do default
                    // keyboard navigation.
                    itemNavigateFromCurrentFocused = false;
                }
            }
            bool handled = false;
            DependencyObject focusedElement = Keyboard.FocusedElement as DependencyObject;
            switch (e.Key)
            {
                case Key.Home:
                    if (IsDropDownOpen)
                    {
                        handled = RibbonHelper.NavigateToNextMenuItemOrGallery(this, -1, BringIndexIntoView);
                    }
                    break;
                case Key.End:
                    if (IsDropDownOpen)
                    {
                        handled = RibbonHelper.NavigateToPreviousMenuItemOrGallery(this, -1, BringIndexIntoView);
                    }
                    break;
                case Key.Down:
                    if (IsDropDownOpen)
                    {
                        if (itemNavigateFromCurrentFocused)
                        {
                            // event could have bubbled up from MenuItem
                            // when it could not navigate to the next item (for eg. gallery)
                            handled = RibbonHelper.NavigateToNextMenuItemOrGallery(this, focusedIndex, BringIndexIntoView);
                        }
                        else
                        {
                            RibbonHelper.MoveFocus(FocusNavigationDirection.Down);
                            handled = true;
                        }
                    }
                    break;

                case Key.Up:
                    if (IsDropDownOpen)
                    {
                        if (itemNavigateFromCurrentFocused)
                        {
                            // event could have bubbled up from MenuItem
                            // when it could not navigate to the previous item (for eg. gallery)
                            handled = RibbonHelper.NavigateToPreviousMenuItemOrGallery(this, focusedIndex, BringIndexIntoView);
                        }
                        else
                        {
                            RibbonHelper.MoveFocus(FocusNavigationDirection.Up);
                            handled = true;
                        }
                    }
                    break;

                case Key.Tab:
                    if (IsDropDownOpen &&
                        (IsFocused || (focusedElement != null && TreeHelper.IsVisualAncestorOf(this, focusedElement))))
                    {
                        if ((Keyboard.Modifiers & ModifierKeys.Shift) == ModifierKeys.Shift)
                        {
                            handled = RibbonHelper.NavigateToPreviousMenuItemOrGallery(this, Items.Count, BringIndexIntoView);
                        }
                        else
                        {
                            handled = RibbonHelper.NavigateToNextMenuItemOrGallery(this, -1, BringIndexIntoView);
                        }
                    }
                    break;
            }

            e.Handled = handled;
        }