An application sends a ZGM_COMBOADDSTRING message to load the in-cell droplist combo box with selection items. This is normally done in response to the ZGN_LOADCOMBO notification message after a ZGM_COMBOCLEAR.
ZGM_COMBOADDSTRING
wParam = 0; //not used; must be zero
lParam = (LPARAM) lpszString; //address of string to add
This message does not return a value.