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1.00 1.50 1.51 1.52
WINDOWS
kbprg kbbuglist
The information in this article applies to:
- The Microsoft Foundation Classes, included with:
Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51, 1.52
SYMPTOMS
VBX Event handlers are not called even though the events have been properly
registered using AfxRegisterVBEvent. You can solve the problem by reducing
the size of the application's DGROUP by, for example, reducing stack size.
CAUSE
There is a bug in the routing mechanism for VBX events. The bug becomes
apparent when an event's registered value is greater than 0xFF00; at which
point, the program will not call the handler for the event because the
routing in CCmdTarget::OnCmdMsg will not route the VBX event as a
registered notification code but as a regular Windows message.
RESOLUTION
VBX events are registered using AfxRegisterVBEvent. The value assigned to
the VBX event is directly related to the amount of space available in the
default data segment. If an application's default data segment is nearing
maximum capacity (0xFFFF), then these values could end up being greater
than 0xFF00. Here are several possible workarounds for this problem:
- Put the module where you have the AfxRegisterVBEvent calls first in the
link order. This ensures that the events are registered before other
heap allocations occur during initialization of other modules. As a
result, the event values tend to be smaller. If you are building the
application from the Visual WorkBench, you can accomplish this by
removing the modules from your project and adding the module with the
AfxRegisterVBEvent calls before the other modules in your project
except a pre-compiled header module, such as STDAFX.CPP.
-or-
- Reduce your application's stack size. To be precise, you need to reduce
the stack size by at MOST 768 bytes.
-or-
- Use other techniques to reduce the size of DGROUP. For more information
on how to do this, please see the following article in the Microsoft
Knowledge Base:
ARTICLE-ID: Q49935
TITLE : PRB: L2028 Error Caused by HEAPSIZE, STACKSIZE and
DGROUP Size
-or-
- Reduce heap allocations done during global initialization. If your
application is built in small/medium memory model, these allocations
will come out of your default data segment. This will not help, however
if you are using the Compact/Large memory model.
-or-
- If your use of VBX controls is limited to one parent window (for
example, all your VBX controls exist on only one window) and you are
handling a limited number of events, you can handle the WM_VBXEVENT
message in the parent window class. Then you can take care of
decoding and handling the particular event and right in the OnVBXEvent
function. Please see MFC TechNote #24 for details.
-or-
- Modify the OnCmdMsg function to route the events correctly. This would
require that you rebuild the MFC libraries, so this solution should be
used as a last resort. For details on rebuilding the MFC Libraries,
please see the section titled "How To Build Other Library Versions"
in the "Class Library User's Guide." Or read the README.TXT file that
can be found in the MFC source directory (the default directory is
\MSVC\MFC\SRC). The modification would be to change the following lines
in CMDTARG.CPP:
From:
// Constant code...
if ((UINT)nCode < 0xC000 || (UINT)nCode > 0xFF00)
To:
if ((UINT)nCode < 0xC000 || (UINT)nCode == 0xFFFF)
And change the following lines:
From:
#endif //_DEBUG
if ((UINT)nCode < 0xC000 || (UINT)nCode > 0xFF00)
To:
#endif //_DEBUG
if ((UINT) nCode < 0xC000 || (UINT)nCode == 0xFFFF)
STATUS
Microsoft has confirmed this to be a bug in the Microsoft products listed
at the beginning of this article. We are researching this problem and will
post new information here in the Microsoft Knowledge Base as it becomes
available.
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