The CBN_EDITUPDATE notification message is sent when the edit-control portion of a combo box is about to display altered text. This notification is sent after the control has formatted the text, but before it displays the text. The parent window of the combo box 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_EDITUPDATE notification message in the high-order word.
This message does not occur if the combo box has the CBS_DROPDOWNLIST style.