Wpf ListBox Scrolling with Keyboard issue

Question

Ok, I have a listbox and have a trigger defined for a listboxitem as follows:

 <DataTrigger Binding="{Binding IsMouseOver,RelativeSource={RelativeSource Self}}" Value="True">
   <Setter Property="IsSelected" Value="True" />
  </DataTrigger>

This works fine as soon as i move my mouse over a listboxitem it gets selected. the problem comes when i try scrolling the list with keyboard down arrow. So assume that my mouse is over the third item in the list and thats selected by default. Now, when I press the down arrow, the first item is selected! Also, when i keeep the down arrow pressed, only the viewable list scrolls properly as soon as the selection moves to an item that was not in view before, the selection is put back on the item on which the mouse was over and scrolling starts from there!...so in other words, the keyboard scrolling works fine when the mouse IS NOT OVER THE LISTBOX at all....I really hope I made myself clear.

I may be doing something silly here and any suggestions are welcome Thanks

kowd kowd · Accepted Answer · 2011-03-10T01:50:50

Wow, this is a most amusing trigger :)

This behavior is kind of expected since the selected item is focused by the ListBoxItem and when the ScrollBar updates the IsMouseOver property changes for the new item below the mouse.

You basically need to disable selecting the item under the mouse if there is keyboard selection going on at the same time:

Hack Warning:

EventManager.RegisterClassHandler(typeof(ListBoxItem), ListBoxItem.SelectedEvent, new RoutedEventHandler(
            (s, e) => e.Handled = (Keyboard.IsKeyDown(Key.Down) || Keyboard.IsKeyDown(Key.Up)) && (s as FrameworkElement).IsMouseOver), true);

Place the above in any static constructor. It is crude but works for me.

Wpf ListBox Scrolling with Keyboard issue

1 Answers