KB133025 - HOWTO: How to Store MFC Printer Information in a Document

MORE INFORMATION

There are two things that need to be considered when storing the printer information in the document:

When copying the information between the application and the document, you must ensure that separate copies of this information are maintained because both the application object and the document free and reallocate memory for the information structures frequently.
You must trap all changes to the application printer information, so that consistency is maintained between it and the current document object.

In the following sections, sample code is given for each of these considerations.

Copying Information

Below is an example of code that could be added to the CWinApp-derived class and CDocument-derived class to safely copy information between the objects. It is assumed that CMyApp is a class derived from CWinApp, CMyDoc is derived from CDocument, and CMyView is derived from CView. You need to add the function prototype for SetPrinterDeviceDefaults to the definition of CMyApp in the header file.

   // Note: for 32-bit compilers, replace occurrences of _fmemcpy()
   //       with memcpy() (or add windowsx.h to your include files)

   void CMyApp::SetPrinterDeviceDefaults(HGLOBAL hDevNames,
                                         HGLOBAL hDevMode)
   {
   // Lock the handles to the structures to get pointers
      LPDEVNAMES pDevNames = (LPDEVNAMES)::GlobalLock(hDevNames);
      LPDEVMODE  pDevMode  = (LPDEVMODE)::GlobalLock(hDevMode);

   // Free the old printer information if it exists
      if (m_hDevNames != NULL)
         ::GlobalFree(m_hDevNames);
      if (m_hDevMode != NULL)
         ::GlobalFree(m_hDevMode);

   // Allocate space for the new printer info structures
      m_hDevNames = ::GlobalAlloc(GPTR, ::GlobalSize(hDevNames));
      m_hDevMode = ::GlobalAlloc(GPTR, ::GlobalSize(hDevMode));

   // Lock the new handles
      LPDEVNAMES m_pDevNames = (LPDEVNAMES)::GlobalLock(m_hDevNames);
      LPDEVMODE  m_pDevMode  = (LPDEVMODE)::GlobalLock(m_hDevMode);

   // Copy the printer information into the document
      _fmemcpy(m_pDevNames, pDevNames,
               (size_t)::GlobalSize(hDevNames));
      _fmemcpy(m_pDevMode, pDevMode,
               (size_t)::GlobalSize(hDevMode));

   // Unlock the handles
      ::GlobalUnlock(hDevNames);
      ::GlobalUnlock(hDevMode);

      ::GlobalUnlock(m_hDevNames);
      ::GlobalUnlock(m_hDevMode);
   }

The function prototype for CMyDoc::SetPrinterDeviceDefaults() should be added to the class definition of CMyDoc in the header file. The following declarations should also be added to CMyDoc: HGLOBAL m_hDevMode; HGLOBAL m_hDevNames; void CMyDoc::SetPrinterDeviceDefaults() { // Allocate the structure to store the returned printer info PRINTDLG printDlg; // Get the printer information AfxGetApp()->GetPrinterDeviceDefaults(&printDlg); // Lock the handles to the structures to get pointers LPDEVNAMES pDevNames = (LPDEVNAMES)::GlobalLock(printDlg.hDevNames); LPDEVMODE pDevMode = (LPDEVMODE)::GlobalLock(printDlg.hDevMode); // Free the old printer information if it exists if (m_hDevNames != NULL) ::GlobalFree(m_hDevNames); if (m_hDevMode != NULL) ::GlobalFree(m_hDevMode); // Allocate space for the new printer info structures m_hDevNames = ::GlobalAlloc(GPTR, ::GlobalSize(printDlg.hDevNames)); m_hDevMode = ::GlobalAlloc(GPTR, ::GlobalSize(printDlg.hDevMode)); // Lock the new handles LPDEVNAMES m_pDevNames = (LPDEVNAMES)::GlobalLock(m_hDevNames); LPDEVMODE m_pDevMode = (LPDEVMODE)::GlobalLock(m_hDevMode); // Copy the printer information into the document _fmemcpy(m_pDevNames, pDevNames, (size_t)::GlobalSize(printDlg.hDevNames)); _fmemcpy(m_pDevMode, pDevMode, (size_t)::GlobalSize(printDlg.hDevMode)); // Unlock the handles ::GlobalUnlock(printDlg.hDevNames); ::GlobalUnlock(printDlg.hDevMode); ::GlobalUnlock(m_hDevNames); ::GlobalUnlock(m_hDevMode); } These routines are similar. They use the same code to allocate a new block of memory and copy the information from one set of structures to the other. This ensures that no matter what the application object or document object does to its respective printer information, the other object is not affected.

Trapping All Changes

Below is a code example that initializes the document's information and traps OnFilePrint and OnFilePrintSetup. OnFilePrintPreview is not included here because its implementation is virtually identical to OnFilePrint.

Here is the modified constructor for the CDocument derived class that initializes the new document with the application's current printer information:

   CMyDoc::CMyDoc()
   {
   // Initialize the handles to the printer information
      m_hDevNames = NULL;
      m_hDevMode = NULL;

   // Initialize printer settings
      SetPrinterDeviceDefaults();
   }

The next two member functions, one from the view and the other from the application, guarantee that the application uses the document's printer information and that the document's information is updated if the user changes it.

CMyView::OnFilePrint is a message handler for the ID_FILE_PRINT message, and CMyApp::OnFilePrintSetup is a message handler for the ID_FILE_PRINT_SETUP message. The message handlers can be added using ClassWizard.

   void CMyView::OnFilePrint()
   {
      CMyDoc* pDoc = GetDocument();

   // Set the application's printer information
      ((CMyApp *)AfxGetApp())->SetPrinterDeviceDefaults(
                                     pDoc->m_hDevNames,
                                     pDoc->m_hDevMode);

      CView::OnFilePrint();

   // Set the new printer information
      pDoc->SetPrinterDeviceDefaults();
   }

   void CMyApp::OnFilePrintSetup()
   {
      CFrameWnd* pFrame = ((CFrameWnd *)m_pMainWnd)->GetActiveFrame();

      CMyDoc* pDoc = (CMyDoc *)pFrame->GetActiveDocument();

   // Set the application's printer information
      SetPrinterDeviceDefaults(pDoc->m_hDevNames, pDoc->m_hDevMode);

      CWinApp::OnFilePrintSetup();

   // Set the new printer information
      pDoc->SetPrinterDeviceDefaults();
   }

Once these code changes are in place, each object derived from the modified document class stores its own printer information. Because this could lead to confusion for users who are used to the standard global printer configuration model, Microsoft recommends that you include the currently selected printer name as part of the document title.

HOWTO: How to Store MFC Printer Information in a Document

SUMMARY

MORE INFORMATION

Copying Information

Trapping All Changes