Advanced MFC Programming

Chapter 14. Views
Original mapping:
ON_COMMAND(ID_FILE_OPEN, CWinApp::OnFileOpen)
New mapping:
ON_COMMAND(ID_FILE_OPEN, OnFileOpen)
Customizing “Save As” Dialog Box
Besides file open, we also need to think about file saving. This is more complex than file open,
because we need to allow the user to save the file being edited with a different format. In case the user
changes data format, we must also change the original file extension (from “rtf” to “txt” or vice versa).
To customize file saving to support multiple file formats, we need to override function CDocument::
DoSave(…). This is an undocumented member function of MFC. Unfortunately, because file dialog box is
implemented within this function, we have no other choice to support multiple file format without
modifying it. Although using undocumented functions is not recommendable, sometimes we have to do so
in order to make our applications perfect.
Function CDocument::DoSave(…) has two parameters:
BOOL CDocument::DoSave(LPCTSTR lpszPathName, BOOL bReplace);
The first parameter is a pointer to the buffers containing the file name, the second is a Boolean type
variable indicating if the file name should be changed. Actually, this parameter is always set to TRUE so
we can neglect its value.
Pointer lpszPathName gives us the file name that should be used for saving data. But this pointer can
also be NULL. If the file being edited is created through File | New command and the user has selected File
| Save or File | Save As command, lpszPathName will be NULL. The following table lists the values of
lpszPathName and bReplace under different situations:
File creation command Save command Value of lpszPathName
File | New File | Save NULL
File | New File | Save As NULL
File | Open File | Save Actual File Path
File | Open File | Save As NULL
Based on the above analysis, we can override function CDocument::DoSave(…) as follows: obtaining
the file name from lpszPathName, if it is NULL, we implement the “Save As” dialog box with multiple file
filters. After the user has selected a file name, we need to add extension to it according to the filter selected
by the user. Also, we need to set data format for file saving. Then we can call function CDocument::
OnSaveDocument(…) and pass the file name to it to implement file saving.
In the derived function CWordPadDoc::DoSave(…), we need to implement the customized “Save As”
dialog box and also, add file extension, change file format if necessary. The following is a portion of this
function:
……
dlg.m_ofn.lpstrFilter=STRING_FILTER;
dlg.m_ofn.nFilterIndex=1;
if(dlg.DoModal() == IDOK)newName=dlg.GetPathName();
else return FALSE;
if(dlg.m_ofn.nFilterIndex == 1)m_bRTF=TRUE;
else m_bRTF=FALSE;
if(bReplace)
{
CString szFind;
if(dlg.m_ofn.nFilterIndex == 1)
{
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