PRB: CScrollView Scroll Range Limited to 32K

• The Microsoft Foundation Classes (MFC) included with: - Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1, 4.2, 5.0

SYMPTOMS

If the scroll range exceeds 32K when you are using the Scroll Thumb to scroll, CScrollView does not handle scrolling correctly. Unusual behavior occurs when you try to scroll beyond 32K.

CAUSE

This behavior is by design. The code to handle ranges greater than 32K was not added to CScrollView because it could fail if a WM_xSCROLL message is sent to the view to programatically scroll the contents.

RESOLUTION

You can work around the problem easily by adding support to handle scroll ranges greater than 32K to a CScrollView derived class. Override the function as follows:

   BOOL CMyScrollView::OnScroll(UINT nScrollCode, UINT nPos, BOOL
                                bDoScroll)
   {
      SCROLLINFO info;
      info.cbSize = sizeof(SCROLLINFO);
      info.fMask = SIF_TRACKPOS;

      if (LOBYTE(nScrollCode) == SB_THUMBTRACK)
      {
         GetScrollInfo(SB_HORZ, &info);
         nPos = info.nTrackPos;
      }

      if (HIBYTE(nScrollCode) == SB_THUMBTRACK)
      {
         GetScrollInfo(SB_VERT, &info);
         nPos = info.nTrackPos;
      }

      return CScrollView::OnScroll(nScrollCode, nPos, bDoScroll);
   }

NOTE: Windows 95 and Win32s only support logical and device coordinates up to 32K. Since CScrollView uses logical units in SetScrollSizes(), you should specify a scroll range < 32K on when using CSrollView derived classes on these operating systems.

(c) Microsoft Corporation 1997, All Rights Reserved. Contributions by Sridhar S. Madhugiri, Microsoft Corporation