Derived GridComboBoxCellRenderer

Hi,

I have derived from a GridComboBoxCellRenderer, and I want to enable the mouse wheel for scrolling thru the items. I added the following code:

public override bool ProcessMouseWheel(MouseEventArgs e)
{
if (this.IsDroppedDown)
{
if (e.Delta < 0)
this.ListBoxPart.TopIndex++;
else
this.ListBoxPart.TopIndex--;
return true;
}
return false;
}

But when I use the wheel nothing happens. During a debug session I found out, that the ListBoxPart.TopIndex++ or -- doesn't have any influence on the value - it remains 0.

Any ideas what's wrong there?

Cheers,
Tom