Call the GetExtendedUI member function to determine whether a combo box has the default user interface or the extended user interface.
The extended user interface can be identified in the following ways:
Clicking the static control displays the list box only for combo boxes with the CBS_DROPDOWNLIST style.
Pressing the DOWN ARROW key displays the list box (F4 is disabled).
Scrolling in the static control is disabled when the item list is not visible (arrow keys are disabled).