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FIX: The CDialog::Create() function returns an incorrect value when a dialog box is created in Visual C++

Article ID: 193099 - View products that this article applies to.

This article was previously published under Q193099

SYMPTOMS

If a dialog box is created via the CDialog::Create() call, and the dialog box's OnInitDialog() (in response to WM_INITDIALOG message) ends the dialog box via EndDialog(), the CDialog::Create() function returns a non-zero value. The CDialog::Create() in this case should return zero.

Because the dialog box was destroyed due to an EndDialog() call in the dialog's OnInitDialog(), CDialog::m_hWnd is NULL in this case.

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CAUSE

An additional test was made in the WM_INITDIALOG code (at line 365 of Dlgcore.cpp), which leads to Create() succeeding even if the window handle is NULL.

MFC code for Visual C++ 5.0:

BOOL CWnd::CreateDlgIndirect(LPCDLGTEMPLATE lpDialogTemplate,

      CWnd* pParentWnd, HINSTANCE hInst)

   {

      // ...

      if (hWnd == NULL)
      {
         // ...
         // .. dump some debug information
         return FALSE;
      }

      ASSERT(hWnd == m_hWnd);
      return TRUE;
   }

MFC code for Visual C++ 6.0:

BOOL CWnd::CreateDlgIndirect(LPCDLGTEMPLATE lpDialogTemplate,

      CWnd* pParentWnd, HINSTANCE hInst)

   {

      // ...
      // Help with error diagnosis (only if WM_INITDIALOG didn't
      // EndDialog())
      if (hWnd == NULL && (m_nFlags &amp; WF_CONTINUEMODAL)) // <--- PROBLEM!!!

{
         // ... dump some debug information.
         return FALSE;
      }

      ASSERT(hWnd == m_hWnd);
      return TRUE;

   }

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RESOLUTION

When calling CDialog::Create check both the return value of CDialog::Create(), and the value of CDialog::m_hWnd. If CDialog::m_hWnd is NULL, then the dialog-box creation is unsuccessful.

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STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been fixed in the Visual Studio 6.0 Service Pack 1.

To obtain this service pack, please see:

http://msdn2.microsoft.com/en-us/vstudio/Aa718362.aspx

(http://msdn2.microsoft.com/en-us/vstudio/Aa718362.aspx)

For more information on the Visual Studio 6.0 Service Pack 1, please see the following articles in the Microsoft Knowledge Base:

193009 INFO: Visual Studio 6.0 Service Pack 1 Readme

(http://support.microsoft.com/kb/193009/EN-US/ )

194022 Visual Studio 6.0 service packs, what, where, why

(http://support.microsoft.com/kb/194022/EN-US/ )

194295 How To Tell That a Visual Studio Service Pack Is Installed

(http://support.microsoft.com/kb/194295/EN-US/ )

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MORE INFORMATION

Modify the code for displaying the dialog box so it also checks against the CDialog::m_hWnd variable. For instance:

 
   // Create a modeless dialog box. In this example, m_pModeless is a
   // member variable of type CModeless where CModeless is a CDialog-
   // derived class. IDD_MODELESS is the ID number of a dialog-box template
   // resource.
   m_pModeless = new CModeless;
   if (m_pModeless->Create(IDD_MODELESS, this) &&
      ::IsWindow(m_pModeless->m_hWnd))
   {
      // ... succeeded in dialog-box creation.
   }
   else
   {
      // ... failed in dialog-box creation.
   }

Steps to Reproduce Behavior

Copy the MFC sample MODELESS from the MSDN CDs.
Use ClassWizard to add an OnInitDialog() message handler (in response to WM_INITDIALOG message) to the CAdderDialog class. CAdderDialog is a CDialog-derived class.

Call EndDialog() in the CAdderDialog::OnInitDialog() as follows:

   BOOL CAdderDialog::OnInitDialog()
   {
      CDialog::OnInitDialog();

      // TODO: Add extra initialization here
      EndDialog(-1);
      return TRUE;  // return TRUE unless you set the focus to a control
               // EXCEPTION: OCX Property Pages should return FALSE
   }

Select Win32 Release build from VC++'s Build\Set Active Configuration menu command.
Build and then run the MODELESS sample.
Click Add in the dialog box. The m_pModeless->Create() call in Modeldlg.cpp file (at line 178) returns TRUE, in this case causing the Add button (for displaying the CAdderDialog modeless dialog box) to be disabled.

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