The LVM_GETCOUNTPERPAGE message calculates the number of items that can fit vertically in the visible area of a list view control when in list or report view. Only fully-visible items are counted. You can send this message explicitly, or by using the ListView_GetCountPerPage macro.
LVM_GETCOUNTPERPAGE wParam = 0; lParam = 0;
Returns the number of fully-visible items if successful. If the current view is icon or small icon view, the return value is the total number of items in the list view control.