The CBN_CLOSEUP notification message is sent when the list box of a combo box is hidden. The control's parent window receives this notification message through a WM_COMMAND message.
wParam
Specifies the identifier of the combo box.
lParam
Specifies the handle of the combo box in the low-order word, and specifies the CBN_CLOSEUP notification message in the high-order word.
This notification message is not sent to a combo box that has the CBS_SIMPLE style.
The order in which notifications will be sent cannot be predicted. In parti-cular, a CBN_SELCHANGE notification may occur either before or after a CBN_CLOSEUP notification.