handling arrow key events on textbox attached AutoCompleteExtender

Hi,

    I use arrow keys(up、down、left、right and enter) to switch focus between mutilple controls like textbox or dropdownlist.
It work fine.If I use an autocomplete textbox with Ajax AutoCompleteExtender and the Ajax AutoCompleteExtender show the
data.I press the up or down arrow key,it switch focus to next control and can not assign value from dropdown list to textbox.

I must know if the AutoCompleteExtender show any value(data) and avoid the up or down arrow key to switch focus to next control.

How can I know the AutoCompleteExtender show any value? Thanks.