An application sends an LB_RESETCONTENT to remove all items from a list box.
LB_RESETCONTENT wParam = 0; // not used; must be zero lParam = 0; // not used; must be zero
This message has no parameters.
This message does not return a value.
If you create the list box with an owner-drawn style but without the LBS_HASSTRINGS style, the owner of the list box receives a WM_DELETEITEM message for each item in the list box.