An assertion failure occurs or some keys do not work as expected when displaying the ATL dialog box object as a modeless dialog box (216503)


The information in this article applies to:

  • The Microsoft Active Template Library (ATL) 3.0, when used with:
    • Microsoft Visual C++, 32-bit Enterprise Edition 5.0
    • Microsoft Visual C++, 32-bit Enterprise Edition 6.0
    • Microsoft Visual C++, 32-bit Professional Edition 5.0
    • Microsoft Visual C++, 32-bit Professional Edition 6.0
    • Microsoft Visual C++, 32-bit Learning Edition 6.0
    • Microsoft Visual C++ .NET (2002)
    • Microsoft Visual C++ .NET (2003)
  • The Microsoft Active Template Library (ATL) 2.1, when used with:
    • Microsoft Visual C++, 32-bit Enterprise Edition 5.0
    • Microsoft Visual C++, 32-bit Enterprise Edition 6.0
    • Microsoft Visual C++, 32-bit Professional Edition 5.0
    • Microsoft Visual C++, 32-bit Professional Edition 6.0
    • Microsoft Visual C++, 32-bit Learning Edition 6.0
    • Microsoft Visual C++ .NET (2002)
    • Microsoft Visual C++ .NET (2003)
This article was previously published under Q216503

SYMPTOMS

The ATL Object Wizard dialog box provides an option to create an ATL dialog box object. However, the following problems are found when displaying the ATL dialog box object as a modeless dialog box from within an ATL .exe project:
  • Clicking OK or Cancel causes an assertion failure.
  • The TAB or accelerator key does not work as expected.

CAUSE

The code generated by the ATL wizard is designed to show the dialog box as a modal dialog box.

RESOLUTION

Add/modify the code below to the ATL .exe project to show the ATL dialog box as modeless dialog box:
  1. The EndDialog() call in both the OnOK() and OnCancel() functions cause the assertion failure. Call DestroyWindow() instead for modeless dialog box. 
    LRESULT OnOK(WORD wNotifyCode, WORD wID, HWND hWndCtl, BOOL& bHandled)
{
   DestroyWindow();
   PostQuitMessage(0); // OPTIONAL - call this to terminate the app.
   return 0;
}

LRESULT OnCancel(WORD wNotifyCode, WORD wID, HWND hWndCtl, BOOL& bHandled)
{
   DestroyWindow();
   PostQuitMessage(0); // OPTIONAL - call this to terminate the app.
   return 0;
}
  2. Modify the GetMessage() loop in the _tWinMain() function so IsDialogMessage() is called for a modeless dialog box. This method takes care of both the tab and accelerator keys processing problem. 
    MSG msg;
while (GetMessage(&msg, 0, 0, 0))
{
   if ((gModelessDlg) && 
      (!::IsDialogMessage(gModelessDlg->m_hWnd,&msg)))
      DispatchMessage(&msg);
}
    Note TranslateMessage() is not required in the GetMessage() loop.

STATUS

This behavior is by design.

MORE INFORMATION

Steps to reproduce the behavior

  1. Use the ATL COM Wizard to generate an ATL .exe project.
  2. Create a dialog box class named CMyDialog:

    Visual C++ 6.0
    1. On the Insert menu, click New ATL Object to insert a dialog box object from the Miscellaneous category of the ATL Object Wizard dialog box.
    2. Name the dialog box class CMyDialog.
    Visual C++ .NET
    1. On the Project menu, click Add Class.
    2. In the Add Class dialog box, select ATL Dialog under Templates, and then click Open.
    3. In the ATL Dialog wizard, name the dialog box class CMyDialog, and then click Finish.
  3. Add the following code to the file that contains the _tWinMain() function to show CMyDialog as a modeless dialog box. 
    // Include the header file for CMyDialog and declare a global variable of 
// CMyDialog type.
#include "mydialog.h" 
CMyDialog* gMainDialog = NULL;

extern "C" int WINAPI _tWinMain(HINSTANCE hInstance, 
   HINSTANCE /*hPrevInstance*/, LPTSTR lpCmdLine, int /*nShowCmd*/)
{
   // ... other stuff

   // Show the CMyDialog as a modeless dialog box.
   gMainDialog = new CMyDialog;
   gMainDialog->Create(GetDesktopWindow());
   gMainDialog->ShowWindow(SW_SHOW);

   MSG msg;
   while (GetMessage(&msg, 0, 0, 0))
      DispatchMessage(&msg);


   // ... other stuff

   // Destroy the C++ object for the modeless dialog box.
   if (gMainDialog)
      delete gMainDialog;  

   // ... other stuff
}

REFERENCES

(c) Microsoft Corporation 1999, All Rights Reserved. Contributions by Yeong-Kah Tam, Microsoft Corporation.
Modification Type:MajorLast Reviewed:10/3/2005
Keywords:kbtshoot kbATLWC kbDlg kbprb KB216503 kbAudDeveloper
©2004 Microsoft Corporation. All rights reserved.