单文档，自定义打开/保存对话框
在多文档下，可以通过在string table添加另外的字符串增加文件类型，如
IDR_MDITYPE：/n图像/n新建图像/n图像文件(*.aaa;*.bbb)/n.aaa;.bbb/nMDI.Document/nMDI.Document
IDR_OtherTYPE：/n文本/n新建文本/n文本文件(*.ccc;*.ddd)/n.ccc;.ddd/nMDI.Document/nMDI.Document
这时，弹出的打开与保存对话框就可以选择相应的文件类型。
但是在单文档情况下，这种办法就不可取了。因为在单文档下，通常只有一个字符串资源和菜单IDR_MAINFRAME，当我们添加IDR_OtherTYPE的字符串资源时，就必须增加相应的菜单资源，这种作法似乎不是MFC的初衷。如画图等程序只有一个菜单，在新建时不会弹出文件类型选择提示框（不同与多文档），而打开和保存时却能选择多种文件类型。要是通过添加字符串来增加文件类型，虽然在打开和保存时能选择多种文件类型，但是新建时会弹出文件类型选择提示框，而且在一个文档打开的情况下，若新建或打开另一类型的文档，不会提示保存当前文档，而是直接在新的窗口打开。这显然与单文档的“定义”不符。为此，此处通过修改CDocManager::DoPromptFileName()来达到打开与保存多种文件类型的目的。工程名为SDI。
首先考虑打开对话框。第一步是要弄清，打开对话框是什么时候（在哪）弹出来的？
默认情况下，CSDIApp调用CWinApp::OnFileOpen方法处理FileOpen事件：
ON_COMMAND(ID_FILE_OPEN, &CWinApp::OnFileOpen)
CWinApp::OnFileOpen又调用CDocManager::OnFileOpen处理FileOpen事件：
void CWinApp::OnFileOpen()
{
ENSURE(m_pDocManager != NULL);
m_pDocManager->OnFileOpen();
}
CDocManager::OnFileOpen显示对话框与用户交互，然后调用CWinApp::OpenDocumentFile方法：
void CDocManager::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
AfxGetApp()->OpenDocumentFile(newName);
// if returns NULL, the user has already been alerted
}
显然，一种可能的解决办法是绕过CWinApp和CDocManager，在CSDIApp::OnFileOpen方法中显示自定义对话框，然后调用CWinApp::OpenDocumentFile方法。
ON_COMMAND(ID_FILE_OPEN, &CSDIApp::OnFileOpen)
void CSDIApp::OnFileOpen()
{
LPCTSTR szFilter = L"图像文件(*.aaa;*.bbb)|*.aaa;*.bbb|文本文件(*.ccc;*.ddd)|*.ccc;*.ddd||";
CFileDialog oFileDlg(TRUE, NULL, NULL, 4|2, szFilter);
if(oFileDlg.DoModal() == IDOK)
OpenDocumentFile(oFileDlg.GetFileName());
// CSDIApp不需要重写CWinApp::OpenDocumentFile方法
}
现在考虑保存对话框。第一步仍然是弄清，保存对话框是什么时候（在哪）弹出来的？
分发消息时，调用了CDocument::DoFileSave虚方法：
BOOL CDocument::DoFileSave()
{
DWORD dwAttrib = GetFileAttributes(m_strPathName);
if (dwAttrib & FILE_ATTRIBUTE_READONLY)
{
// we do not have read-write access or the file does not (now) exist
if (!DoSave(NULL))
{
TRACE(traceAppMsg, 0, "Warning: File save with new name failed./n");
return FALSE;
}
}
else
{
if (!DoSave(m_strPathName))
{
TRACE(traceAppMsg, 0, "Warning: File save failed./n");
return FALSE;
}
}
return TRUE;
}
CDocument::DoFileSave调用CDocument::DoSave，也是一个虚方法：（注：没有DoSaveAs方法，lpszPathName参数决定了CDocument::DoSave是表现为“保存”还是“另存为”。）
BOOL CDocument::DoSave(LPCTSTR lpszPathName, BOOL bReplace /*= TRUE*/)
// Save the document data to a file
// lpszPathName = path name where to save document file
// if lpszPathName is NULL then the user will be prompted (SaveAs)
// note: lpszPathName can be different than 'm_strPathName'
// if 'bReplace' is TRUE will change file name if successful (SaveAs)
// if 'bReplace' is FALSE will not change path name (SaveCopyAs)
{
CString newName = lpszPathName;
if (newName.IsEmpty())
{
CDocTemplate* pTemplate = GetDocTemplate();
ASSERT(pTemplate != NULL);
newName = m_strPathName;
if (bReplace && newName.IsEmpty())
{
newName = m_strTitle;
// check for dubious filename
int iBad = newName.FindOneOf(_T(":///"));
if (iBad != -1)
newName.ReleaseBuffer(iBad);
// append the default suffix if there is one
CString strExt;
if (pTemplate->GetDocString(strExt, CDocTemplate::filterExt) &&
!strExt.IsEmpty())
{
ASSERT(strExt[0] == '.');
int iStart = 0;
newName += strExt.Tokenize(_T(";"), iStart);
}
}
if (!AfxGetApp()->DoPromptFileName(newName,
bReplace ? AFX_IDS_SAVEFILE : AFX_IDS_SAVEFILECOPY,
OFN_HIDEREADONLY | OFN_PATHMUSTEXIST, FALSE, pTemplate))
return FALSE; // don't even attempt to save
}
CWaitCursor wait;
if (!OnSaveDocument(newName))
{
if (lpszPathName == NULL)
{
// be sure to delete the file
TRY
{
CFile::Remove(newName);
}
CATCH_ALL(e)
{
TRACE(traceAppMsg, 0,
"Warning: failed to delete file after failed SaveAs./n");
DELETE_EXCEPTION(e);
}
END_CATCH_ALL
}
return FALSE;
}
// reset the title and change the document name
if (bReplace)
SetPathName(newName);
return TRUE; // success
}
CDocument::DoSave虚方法调用CWinApp::DoPromptFileName方法弹出保存对话框，后者又调用CDocManager::DoPromptFileName虚方法（情形与打开文件时相同）：
BOOL CDocManager::DoPromptFileName(CString& fileName, UINT nIDSTitle,
DWORD lFlags, BOOL bOpenFileDialog, CDocTemplate* pTemplate)
{
CFileDialog dlgFile(bOpenFileDialog, NULL, NULL,
OFN_HIDEREADONLY | OFN_OVERWRITEPROMPT, NULL, NULL, 0);
CString title;
VERIFY(title.LoadString(nIDSTitle));
dlgFile.m_ofn.Flags |= lFlags;
CString strFilter;
CString strDefault;
if (pTemplate != NULL)
{
ASSERT_VALID(pTemplate);
_AfxAppendFilterSuffix(strFilter, dlgFile.m_ofn, pTemplate, &strDefault);
}
else
{
// do for all doc template
POSITION pos = m_templateList.GetHeadPosition();
BOOL bFirst = TRUE;
while (pos != NULL)
{
pTemplate = (CDocTemplate*)m_templateList.GetNext(pos);
_AfxAppendFilterSuffix(strFilter, dlgFile.m_ofn, pTemplate,
bFirst ? &strDefault : NULL);
bFirst = FALSE;
}
}
// append the "*.*" all files filter
CString allFilter;
VERIFY(allFilter.LoadString(AFX_IDS_ALLFILTER));
strFilter += allFilter;
strFilter += (TCHAR)'/0'; // next string please
strFilter += _T("*.*");
strFilter += (TCHAR)'/0'; // last string
dlgFile.m_ofn.nMaxCustFilter++;
dlgFile.m_ofn.lpstrFilter = strFilter;
dlgFile.m_ofn.lpstrTitle = title;
dlgFile.m_ofn.lpstrFile = fileName.GetBuffer(_MAX_PATH);
INT_PTR nResult = dlgFile.DoModal();
fileName.ReleaseBuffer();
return nResult == IDOK;
}
AFX_STATIC void AFXAPI _AfxAppendFilterSuffix(CString& filter, OPENFILENAME& ofn,
CDocTemplate* pTemplate, CString* pstrDefaultExt)
{
ENSURE_VALID(pTemplate);
ASSERT_KINDOF(CDocTemplate, pTemplate);
CString strFilterExt, strFilterName;
if (pTemplate->GetDocString(strFilterExt, CDocTemplate::filterExt) &&
!strFilterExt.IsEmpty() &&
pTemplate->GetDocString(strFilterName, CDocTemplate::filterName) &&
!strFilterName.IsEmpty())
{
if (pstrDefaultExt != NULL)
pstrDefaultExt->Empty();
// add to filter
filter += strFilterName;
ASSERT(!filter.IsEmpty()); // must have a file type name
filter += (TCHAR)'/0'; // next string please
int iStart = 0;
do
{
CString strExtension = strFilterExt.Tokenize( _T( ";" ), iStart );
if (iStart != -1)
{
// a file based document template - add to filter list
// If you hit the following ASSERT, your document template
// string is formatted incorrectly. The section of your
// document template string that specifies the allowable file
// extensions should be formatted as follows:
// .<ext1>;.<ext2>;.<ext3>
// Extensions may contain wildcards (e.g. '?', '*'), but must
// begin with a '.' and be separated from one another by a ';'.
// Example:
// .jpg;.jpeg
ASSERT(strExtension[0] == '.');
if ((pstrDefaultExt != NULL) && pstrDefaultExt->IsEmpty())
{
// set the default extension
*pstrDefaultExt = strExtension.Mid( 1 ); // skip the '.'
ofn.lpstrDefExt = const_cast< LPTSTR >((LPCTSTR)(*pstrDefaultExt));
ofn.nFilterIndex = ofn.nMaxCustFilter + 1; // 1 based number
}
filter += (TCHAR)'*';
filter += strExtension;
filter += (TCHAR)';'; // Always append a ';'. The last ';' will get replaced with a '/0' later.
}
} while (iStart != -1);
filter.SetAt( filter.GetLength()-1, '/0' );; // Replace the last ';' with a '/0'
ofn.nMaxCustFilter++;
}
}
看起来，重写CDocManager::DoPromptFileName方法比重写CDocument::DoSave方法要省事些：
BOOL CSDIDocMgr::DoPromptFileName(CString& fileName, UINT nIDSTitle,
DWORD lFlags, BOOL bOpenFileDialog, CDocTemplate* pTemplate)
{
LPCTSTR strFilter = L"图像文件(*.aaa)/0*.aaa/0文本文件 (*.bbb)/0*.bbb/0/0";
CFileDialog dlgFile(bOpenFileDialog, NULL, NULL, OFN_HIDEREADONLY | OFN_OVERWRITEPROMPT, strFilter, NULL, 0);
CString title;
VERIFY(title.LoadString(nIDSTitle));
dlgFile.m_ofn.lpstrFilter = strFilter;
dlgFile.m_ofn.lpstrDefExt = _T(".aaa");
dlgFile.m_ofn.lpstrTitle = title;
dlgFile.m_ofn.lpstrFile = fileName.GetBuffer(_MAX_PATH);
INT_PTR nResult = dlgFile.DoModal();
fileName.ReleaseBuffer();
return nResult == IDOK;
}
CSDIDocMgr是派生自CDocManager的类。下一步的问题是：怎么为CWinApp::m_pDocManager创建CSDIDocMgr对象（而非CDocManager对象）？m_pDocManager是在重写的CWinApp::InitInstance虚方法中创建的，具体来说，是在CWinApp::AddDocTemplate方法中创建的，CWinApp::AddDocTemplate方法在创建m_pDocManager之前会检查它是否为NULL，只有当m_pDocManager为NULL时才为它创建CDocManager对象，所以现在并不需要重写CWinApp::AddDocTemplate方法，而只需要在重写的CWinApp::InitInstance方法中、在调用CWinApp::AddDocTemplate方法之前为m_pDocManager创建CSDIDocMgr对象。
一旦重写了CDocManager::DoPromptFileName方法，之前提到的自定义打开对话框文件扩展名的方法也就多此一举了，也不再需要修改资源文件中的IDR_DTriNetTYPE字段，因为无论打开还是保存对话框，最终都是由CDocManager::DoPromptFileName执行的。