All the Dynamic Data Exchange (DDE) messages are discarded when a Microsoft Foundation Classes (MFC) application displays a modal dialog box (280467)

MORE INFORMATION

1. Add the following definitions to your CMainFrame class:

   // Attributes
   private:
       // if TRUE cache the DDE requests received while the window is disabled
       BOOL          m_bEnableDdeCmdCaching;
       // Array of strings that holds the cached DDE commands
       CStringArray  m_aStrDdeCmd;
   
   // Operations
   public:
       void          EnableDdeCmdCaching()
                     { m_bEnableDdeCmdCaching = TRUE; }
       int           FlushDdeCmdCache();
   					

2. Add a message handler declaration for WM_DDE_EXECUTE in your CMainFrame declaration:

   afx_msg LRESULT OnDDEExecute(WPARAM wParam, LPARAM lParam);

3. Add the following entry in CMainFrame's message map:

   ON_MESSAGE(WM_DDE_EXECUTE, OnDDEExecute)
   					

4. Add a

   #include <dde.h>

   in CMainFrame's implementation file and the following function implementations:

   // Handle the WM_DDE_EXECUTE message and batch the DDE request for later
   LRESULT CMainFrame::OnDDEExecute(WPARAM wParam, LPARAM lParam)
   {
       if ( !IsWindowEnabled() && m_bEnableDdeCmdCaching )
       {
           UINT unused;
           HGLOBAL hData;
           VERIFY(UnpackDDElParam(WM_DDE_EXECUTE, lParam, &unused, (UINT*)&hData));
   
           // get the command string
           LPCTSTR lpsz = (LPCTSTR) GlobalLock(hData);
   
           // Cache the command string for later
           m_aStrDdeCmd.Add(CString(lpsz));
   
           GlobalUnlock(hData);
       }
   
       return CMDIFrameWnd::OnDDEExecute(wParam, lParam);
   }
   
   // Returns the number of successfully satisfied "open" requests
   int CMainFrame::FlushDdeCmdCache()
   {
       if ( !IsWindowEnabled() )
           return -1;
   
       int nSuccessOpen = 0;
       for ( int i = 0; i <= m_aStrDdeCmd.GetUpperBound ( ); i++ )
       {
           if ( !AfxGetApp()->OnDDECommand((LPTSTR)(LPCTSTR) m_aStrDdeCmd[i]) )
               TRACE1("Error: failed to execute DDE command '%s'.\n", m_aStrDdeCmd[i]);
           else if ( m_aStrDdeCmd[i].Left(7) == _T("[open(\"") )
           {
               nSuccessOpen++;
           }
       }
       m_aStrDdeCmd.RemoveAll();
       m_bEnableDdeCmdCaching = FALSE;
   
       return nSuccessOpen;
   }
   					

5. Next, everywhere that you bring up a modal dialog box that must allow for the DDE commands to be executed, do something like the following:

   CMainFrame *pMainFrame = (CMainFrame*) AfxGetMainWnd();
   pMainFrame->EnableDdeCmdCaching();
   
   // Display the modal dialog that disables the main frame
   CAboutDlg dlg;
   dlg.DoModal();
   
   // Handle the possible batched DDE commands
   pMainFrame->FlushDdeCmdCache();
   					

6. If used in the CWinApp::InitInstance() override, you might want to suppress the opening of a blank new document when the user attempts to open a document during the dialog box display. This can be achieved through code like the following:

   // ...
   // Enable DDE Execute open
   EnableShellOpen();
   RegisterShellFileTypes(TRUE);
   
   pMainFrame->EnableDdeCmdCaching();
   
   CPasswordDlg dlg;
   if ( dlg.DoModal() != IDOK || dlg.NotValidPassword() )
           return FALSE;
   
   int nOpen = pMainFrame->FlushDdeCmdCache();
   
   // Parse command line for standard shell commands, DDE, file open
   CCommandLineInfo cmdInfo;
   ParseCommandLine(cmdInfo);
   
   if ( nOpen > 0 && cmdInfo.m_nShellCommand == CCommandLineInfo::FileNew )
           cmdInfo.m_nShellCommand = CCommandLineInfo::FileNothing;
   // ... 
   					

Steps to Reproduce Behavior

1. Create a new MFC MDI application. In step 4 specify the extension ".zzz".
2. Run the application, and from the File menu, choose Save as in order to create two files, A1.zzz and A2.zzz.
3. Close all open files.
4. Open the About dialog box.
5. Switch to Windows Explorer and double-click A1.zzz.Result: Nothing happens.
   
   Expected result: The file opens in your application.