PRB: MFC Does Not Reopen an Open Document (139828)

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.

/* 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()