Q139828: PRB: MFC Does Not Reopen an Open Document

Article: Q139828
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbDocView kbFileIO kbMFC kbVC100 kbVC150 kbVC200 kbVC400 kbGrpDSMFCATL
Last Modified: 06-MAY-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++, versions 1.0, 1.5, 1.51, 1.52 
   - Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 2.1, 2.2, 4.0 
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SYMPTOMS
========

In a default MFC AppWizard application, the framework will not reopen a document
file from disk that is currently open in the application.

RESOLUTION
==========

This is by design. In a typical MFC application, the Open File command is mapped
to the CWinApp::OnFileOpen() function. In earlier versions of MFC, this function
in turn called the CWinApp::OpenDocumentFile() function. Since MFC 4.0, there is
now an intervening CDocManager class, but the call to OnFileOpen() still
eventually results in a call to CWinApp::OpenDocumentFile().

CWinApp::OpenDocumentFile() first processes the string holding the requested file
name. Then it searches through the list of document templates that were added
for the application by calls to AddDocTemplate in order to find the best match
between the name of the file and a document template to open it with. At this
point, if OpenDocumentFile() finds that this file is already currently opened
for one of the templates, OpenDocumentFile() activates the view for that file
and then returns. It does not re-open the file.

If that document file is not currently open and OpenDocumentFile() has found a
valid template to open the file with, it calls that template's
OpenDocumentFile() function. This function is responsible for opening the file
and loading its data into an appropriate document.

In some situations, you may want to reopen an open document. For example, Notepad
does this. On a file open request, Notepad first displays a prompt dialog to
allow the user to save a modified file. If the user does not click cancel on
this dialog box, Notepad then brings up the File Open dialog box. If the user
chooses to reopen the current file, Notepad rereads it from disk and discards
any unsaved changes.

To duplicate this behavior in an MFC program, the programmer needs to override
the OpenDocumentFile() member function of CWinApp. Or, if the appropriate
template for the file is easy to determine (such as when the application has
only one kind of doc template), it would be possible to call the template's
OpenDocumentFile() directly from an override of CWinApp::OnFileOpen(). This is
demonstrated in the "Sample Code" section of this article.

Note that MFC will display the Save Modified prompt dialog after the Open File
dialog box; this is counter to the behavior of Notepad.

STATUS
======

This behavior is by design.

MORE INFORMATION
================

Sample Code
-----------

  /* Compile options needed: none
  */ 

  void CWinApp::OnFileOpen()
  {
     // prompt the user (with all document templates)
     CString newName;
     if (!DoPromptFileName(newName, AFX_IDS_OPENFILE,
            OFN_HIDEREADONLY | OFN_FILEMUSTEXIST, TRUE, NULL))
         return; // open cancelled

     // Process newName string if necessary

     // Get pTemplate, a pointer to one of the app's document templates

     pTemplate->OpenDocumentFile(newName);
  } // end of CWinApp::OnFileOpen()

(c) Microsoft Corporation 1999, All Rights Reserved.
Contributions by Jason Strayer, Microsoft Corporation


Additional query words: 1.00 1.50 2.00 2.10 2.20 4.00 2.50 2.51 2.52 3.00 3.10 3.20

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Keywords          : kbDocView kbFileIO kbMFC kbVC100 kbVC150 kbVC200 kbVC400 kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:
Issue type        : kbprb

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