void ShowDropDown( BOOL bShowIt = TRUE );
bShowIt
Specifies whether the drop-down list box is to be shown or hidden. A value of TRUE shows the list box. A value of FALSE hides the list box.
Shows or hides the list box of a combo box that has the CBS_DROPDOWN or CBS_DROPDOWNLIST style. By default, a combo box of this style will show the list box.
This member function has no effect on a combo box created with the CBS_SIMPLE style.
CB_SHOWDROPDOWN