An application sends a LB_RESETCONTENT to remove all items from a list box.
wParam
This parameter is not used.
lParam
This parameter is not used.
This message always returns TRUE.
If the list box was created with an owner-draw style but without the LBS_HASSTRINGS style, the owner of the combo box receives a WM_DELETEITEM message for each item in the combo box.
WM_DELETEITEM