+ assert(c && c->ctrl->generic.type == CTRL_LISTBOX);
+ if (c->ctrl->listbox.multisel) {
+ assert(c->ctrl->listbox.height != 0); /* not combo box */
+ ret = SendDlgItemMessage(dp->hwnd, c->base_id+1, LB_GETSELCOUNT, 0, 0);
+ if (ret == LB_ERR || ret > 1)
+ return -1;
+ }