FIX: Asserts When Creating a Dialog Box in an MFC Regular DLL
ID: Q194300
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The information in this article applies to:
-
The Microsoft Foundation Classes (MFC), used with:
-
Microsoft Visual C++, 32-bit Editions, version 6.0
SYMPTOMS
When an MFC EXE SDI/MDI application in the context of a command handler
calls an exported function in MFC regular DLL, which creates a MFC modal
dialog box, the following asserts may be triggered:
ASSERT in wincore.cpp line 884
ASSERT in wincore.cpp line 883
If the asserts are ignored, the behavior of the application is normal. The
EXE and regular DLL must be dynamically linked to MFC.
CAUSE
When a parent is not explicitly specified for a modal dialog box, MFC in
the PreModal() call determines the parent with a call to
CWnd::GetSafeOwner_(). This call returns the routing frame
(AfxGetThreadState()->m_pRoutingFrame). m_pRoutingFrame is assigned in a
command handler. [See CPushRoutingFrame in CFrameWnd::OnCmdMsg()].
The routing frame is set in the command handler in the EXE, to a frame
window of the EXE. Because the thread state is the same in the EXE and the
DLL, AfxGetThreadState()->m_pRoutingFrame returns the EXE frame window. A temporary CWnd is created, in the temporary handle map of the DLL, for the routing frame in the CDialog::PreModal() call when calling
CWnd::FromHandle(::GetActiveWindow()). This assert, in CWnd::AssertValid(),
is caused by the fact that routing frame does not match the temporary CWnd
present in the temporary handle map of the regular DLL.
This problem affects all modal windows that are created in a command
handler in the context of a regular DLL, where CWnd::GetSafeOwner_() is
called. CWnd::GetSafeOwner_() is called during the creation of modal
windows. This includes MFC message boxes, OLE property sheets,
CDatabase::Connect, dialogs boxes, property sheets, and OLE busy dialog
boxes. Note that this problem does not affect modeless windows because
CWnd::GetSafeOwner_() is not called in this context.
RESOLUTION
One workaround is to temporarily set AfxGetThreadState()->m_pRoutingFrame
to NULL for the duration of the DoModal() call. The following code can be
used:
class tempRoutingFrame {
CFrameWnd* m_pFrame ;
public:
tempRoutingFrame(CFrameWnd * pWnd= NULL)
{
// Save current value
m_pFrame = AfxGetThreadState()->m_pRoutingFrame;
// Set to value passed in. NULL by default.
AfxGetThreadState()->m_pRoutingFrame = pWnd;
}
~tempRoutingFrame()
{
// Restore m_pRoutingFrame to original value.
AfxGetThreadState()->m_pRoutingFrame = m_pFrame;
}
};
extern "C" void __declspec(dllexport) TestFunction();
void TestFunction()
{
AFX_MANAGE_STATE(AfxGetStaticModuleState())
#ifdef _DEBUG
// Workaround for ASSERT in WINCORE.CPP 884 (CWnd::AssertValid)
tempRoutingFrame rframe;
#endif
CMyDialog dlg;
dlg.DoModal();
}
Another workaround, in the case of dialog boxes and property sheets, is to
explicitly set the parent of the dialog box as follows:
void TestFunction()
{
AFX_MANAGE_STATE(AfxGetStaticModuleState())
CMyDialog dlg(AfxGetMainWnd());
dlg.DoModal();
}
STATUS
Microsoft has confirmed this to be a bug in the Microsoft products listed
at the beginning of this article.
This bug was corrected in Visual Studio 6.0 Service Pack 3.
For more information about Visual Studio service packs, please see the following articles in the Microsoft Knowledge Base:
Q194022 INFO: Visual Studio 6.0 Service Packs, What, Where, Why
Q194295 HOWTO: Tell That Visual Studio 6.0 Service Packs Are Installed
MORE INFORMATION
Steps to Reproduce Behavior
- Create a regular MFC DLL project using the App Wizard.
- Create a new dialog box resource with one edit control, and OK and CANCEL buttons.
- Create a class for the dialog box derived from CDialog. Name this class CMyDialog.
- Add the following function in mydialog.cpp:
extern "C" void __declspec(dllexport) TestFunction();
void TestFunction()
{
AFX_MANAGE_STATE(AfxGetStaticModuleState());
CMyDialog dlg;
dlg.DoModal();
}
- Build the DLL.
- Create a default App Wizard application EXE project.
- Replace the OnAppAbout function with the following:
extern "C" void __declspec(dllimport) TestFunction();
void CMyTestApp::OnAppAbout()
{
TestFunction();
}
- Add the export library created in step 5 to the project created in step 6.
- Copy the DLL built in step 5 to the debug folder for the application
built in step 6.
- Build and run.
- On the Help menu, click About.
RESULTS: ASSERTS in wincore.cpp, lines 883 and 884 are triggered.
REFERENCES
TN058: MFC Module State Implementation
© Microsoft Corporation 1998, All Rights Reserved.
Contributions by Mike Francis, Microsoft Corporation
Keywords : kbservicepack kbVC600bug kbVS600sp2 kbVS600SP1 kbVS600sp3fix kbMFC600bug
Version : winnt:6.0
Platform : winnt
Issue type : kbbug