MSG_NEXT_PAGE
fNext = new BButton(bounds, "next", "Next page", new BMessage(MSG_NEXT_PAGE));
case MSG_NEXT_PAGE:
fNext = new BButton(BRect(left, top, left+10, top+10), "Next", "Next Page", new BMessage(MSG_NEXT_PAGE));
case MSG_NEXT_PAGE: fPreview->ShowNextPage();