BUG: Scroll Bars May Be Re-Enabled or Crash Application When Clicked

ID: Q199538

The information in this article applies to:

Microsoft Visual C++, Macintosh Cross-Development Addon, versions 4.0, 4.0b

SYMPTOMS

When clicking a disabled scroll bar of a window, the scroll bar becomes enabled. If the mouse click occurs where the scroll thumb would be, the application crashes.

CAUSE

There is a bug in the Windows Portability Layer.

RESOLUTION

Set the scroll range to 0, 0 (zero, zero) using SetScrollSizes() or SetScrollInfo().

STATUS

Microsoft has confirmed this to be a problem in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

When a window has its scroll bar enabled, and is disabled using the following code


   // hWnd is a handle to window
   EnableScrollBar(hWnd, SB_BOTH, ESB_DISABLE_BOTH);

then the scroll bars are enabled if the user generates a mousedown in the disabled scroll bar. If the mousedown occurs where the scroll thumb would be, the application crashes with the following error message:

Sorry, a system error occurred.
"myapplication"
Bus error

This problem appears for the scroll bar of a combo box but does not appear for the scroll-bar control. This fails with both PowerPC and 68KB platforms.

The workaround is to set the scroll range to 0, 0, as demonstrated below:


   SCROLLINFO si;
   si.cbSize = sizeof(SCROLLINFO);
   si.fMask = SIF_RANGE;
   si.nMin = si.nMax = 0;
   SetScrollInfo(hWnd, SB_HORZ, &si, TRUE);
   SetScrollInfo(hWnd, SB_VERT, &si, TRUE);

REFERENCES

Additional query words: CScrollView CComboBox CScrollBar bus error scrollbar

Keywords : kbui kbMAC kbMFC KbUIDesign kbVC kbDSupport MacPrgIss
Version : MACINTOSH:4.0,4.0b
Platform : MACINTOSH
Issue type : kbbug