How to enhance the method of using the Open File common dialog class with multiple extension filters

MORE INFORMATION

1. The open file dialog box is used to open a file, not save one.
2. The flag OFN_ALLOWMULTISELECT is not specified in the m_ofn.Flags member variable.
3. The m_ofn.lpstrDefExt variable specifies a NULL default extension.

Step-by-step procedure

1. Using ClassWizard, add a new class derived from CFileDialog, and name it CMultiExtFilterFileDialog.
2. Using ClassWizard, add a new BOOL variable, m_bFileMustExist, to the new class.
3. Add the following line to your implementation file:

   #define WM_SETUP_FLAGS  WM_APP+0x500
   						

   Your dialog uses this as a private internal message.
4. Add overrides for the DoModal() and OnFileNameOK() functions.
5. In the dialog implementation file, define the DoModal() override as follows:

   int CMultiExtFilterFileDialog::DoModal()
   {
       // If opening a file, and multi select is not enabled,
       // and no default extension is specified:
       if (m_bOpenFileDialog && !(m_ofn.Flags & OFN_ALLOWMULTISELECT) &&
           !m_ofn.lpstrDefExt)
       {
           m_bFileMustExist = m_ofn.Flags & OFN_FILEMUSTEXIST;
           m_ofn.Flags &= ~OFN_FILEMUSTEXIST;
       }
   
       return CFileDialog::DoModal();
   }
   					

6. In the dialog implementation file, define the OnFileNameOK() override as follows:

   BOOL CMultiExtFilterFileDialog::OnFileNameOK()
   {
       // If saving, or if multi select is enabled, or a default extension
       // is available, preserve original functionality:
       if (!m_bOpenFileDialog ||
           (m_ofn.Flags & OFN_ALLOWMULTISELECT) ||
           (m_ofn.lpstrDefExt))
           return CFileDialog::OnFileNameOK();
   
       CString strFName = GetPathName();
       WIN32_FIND_DATA fd;
   
       // Use if the file exists as specified in the file name edit box:
       if (::FindFirstFile(strFName, &fd) != INVALID_HANDLE_VALUE)
       {
           // Accept file name:
           return 0;
       }
       // Use if a file extension was specified:
       if (strFName.ReverseFind('.') > strFName.ReverseFind('\\'))
       {
           // Reject file name:
           return 1;
       }
   
       CString strMultiExt, strExt;
   
       // Get current filter extensions:
       AfxExtractSubString(strMultiExt, m_ofn.lpstrFilter,
           2*m_ofn.nFilterIndex - 1, (TCHAR)'\0');
   
       // For every extension in the filter:
       for (int i = 0;
           AfxExtractSubString(strExt, strMultiExt, i, (TCHAR)';');
           i++)
       {
           // No '*' is allowed in filter extensions:
           if (_tcsrchr((LPCTSTR)strExt + 1, (TCHAR)'*'))
               continue;
           if (INVALID_HANDLE_VALUE !=
               ::FindFirstFile(strFName+((LPCTSTR)strExt+1), &fd))
           {
               unsigned int flen = _tcslen(m_ofn.lpstrFile);
               // If the buffer is not big enough, ignore this extension:
               if (flen + strExt.GetLength() > m_ofn.nMaxFile)
                   continue;
   
               _tcscpy(m_ofn.lpstrFile + flen, (LPCTSTR)strExt+1);
               // Accept the file name:
               return 0;
           }
       }
   
       // To get FileMustExist validation, reset the flag:
       if (m_bFileMustExist)
       {
           // Set the file exist check back to the original:
           m_ofn.Flags |= OFN_FILEMUSTEXIST;
           // Get default processing (for instance, the file must exist 
           // message box):
           PostMessage(WM_KEYDOWN, (WPARAM)(VK_RETURN), (LPARAM)(1));
           // Reset the file exist check:
           PostMessage(WM_SETUP_FLAGS);
           return 1;
       }
       else
           return 0;
   }
   					

7. Finally, provide a handler for the user message specified in step 3:
   1. In your header file, in the declaration of multiExtFilterFileDialog, add the following lines:

      class CMultiExtFilterFileDialog: public CFileDialog
      {
          // ...
          afx_msg LRESULT OnSetupFlags(WPARAM, LPARAM);  // <-- Add this
          DECLARE_MESSAGE_MAP()
      };
      							

   2. In your implementation file, add the following code:

      
      BEGIN_MESSAGE_MAP(CMultiExtFilterFileDialog, CFileDialog)
          //{{AFX_MSG_MAP(CMultiExtFilterFileDialog)
          //}}AFX_MSG_MAP
          ON_MESSAGE(WM_SETUP_FLAGS, OnSetupFlags)
      END_MESSAGE_MAP()
      
      
      LRESULT CMultiExtFilterFileDialog::OnSetupFlags(WPARAM, LPARAM)
      {
          if (m_bFileMustExist)
              m_ofn.Flags &= ~OFN_FILEMUSTEXIST;
          return 0;
      }
      							

TCHAR szFilters[] =
    _T("Text Files (*.txt;*.log;*.bak)\0*.txt;*.log;*.bak\0")
    _T("C++ Files (*.cc;*.cpp;*.h;*.hpp)\0*.cc;*.cpp;*.h;*.hpp\0");
CMultiExtFilterFileDialog ofdlg(TRUE);
ofdlg.m_ofn.lpstrFilter = szFilters;
if (ofdlg.DoModal() == IDOK)
{
    AfxGetApp()->m_pDocManager->OpenDocumentFile(ofdlg.m_ofn.lpstrFile);
}