CBN_EDITUPDATE
idComboBox = LOWORD(wParam);
hwndComboBox = (HWND)lParam;
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.
idComboBox
Value of low word of wParam. Specifies the combo-box ID.
hwndComboBox
Value of lParam. Specifies the combo-box window handle.
This message does not occur if the combo box does not contain an edit control.
WM_COMMAND