PRB: Problems Showing an ATL Dialog Box as Modeless in ATL .exe

• The Microsoft Active Template Library (ATL), versions 2.1, 3.0, included with:
  • Microsoft Visual C++, 32-bit Editions, versions 5.0, 6.0

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 doesn't 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 Behavior

1. Use the ATL COM Wizard to generate an ATL .exe project.



2. On the Insert menu, click New ATL Object to insert a dialog box object from the Micellaneous category of the ATL Object Wizard dialog box. Name the dialog box class, CMyDialog.



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.

Additional query words:

Keywords          : kbATL210 kbATLWC kbVC500 kbVC600 kbATL300 
Version           : WINDOWS:2.1,3.0
Platform          : WINDOWS 
Issue type        : kbprb 

Last Reviewed: March 5, 1999