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MFC多文档程序，从菜单关闭一个文档和直接点击右上角的x效果不同
若文档内容有修改，则前者会询问用户，是否保存修改；后者不保存修改直接关闭。
原因在于，从菜单关闭时，调用OnClose，一定会调用SaveModified()，其源码如下
/
// Standard file menu commandsvoid CDocument::OnFileClose()
{if (!SaveModified())return;// shut it downOnCloseDocument();// this should destroy the document
}
而点击x关闭时，CanCloseFrame()函数会判断是否保存文档，其源码如下：
BOOL CDocument::CanCloseFrame(CFrameWnd* pFrameArg)// permission to close all views using this frame// (at least one of our views must be in this frame)
{ASSERT_VALID(pFrameArg);UNUSED(pFrameArg); // unused in release buildsPOSITION pos = GetFirstViewPosition();while (pos != NULL){CView* pView = GetNextView(pos);ASSERT_VALID(pView);CFrameWnd* pFrame = pView->GetParentFrame();// assume frameless views are ok to closeif (pFrame != NULL){// assumes 1 document per frameASSERT_VALID(pFrame);if (pFrame->m_nWindow > 0)return TRUE; // more than one frame refering to us}}// otherwise only one frame that we know aboutreturn SaveModified();
}
可见，仅当父框架的窗口为0时才会执行SaveModified()语句，其余情况都只会返回TRUE。在使用多文档编程时，要注意为了文档的安全，在自己重载的CanCloseFrame()中加上SaveModified()语句。
如何默默保存，不询问用户？
CDocument::SaveModified()的实现如下：
BOOL CDocument::SaveModified()
{if (!IsModified())return TRUE; // ok to continue// get name/title of documentCString name;if (m_strPathName.IsEmpty()){// get name based on captionname = m_strTitle;if (name.IsEmpty())VERIFY(name.LoadString(AFX_IDS_UNTITLED));}else{// get name based on file title of path namename = m_strPathName;if (afxData.bMarked4){AfxGetFileTitle(m_strPathName, name.GetBuffer(_MAX_PATH), _MAX_PATH);name.ReleaseBuffer();}}CString prompt;AfxFormatString1(prompt, AFX_IDP_ASK_TO_SAVE, name);switch (AfxMessageBox(prompt, MB_YESNOCANCEL, AFX_IDP_ASK_TO_SAVE)){case IDCANCEL:return FALSE; // don't continuecase IDYES:// If so, either Save or Update, as appropriateif (!DoFileSave())return FALSE; // don't continuebreak;case IDNO:// If not saving changes, revert the documentbreak;default:ASSERT(FALSE);break;}return TRUE; // keep going
}
可见，真正执行“保存”动作的是DoFileSave()，因此开发者可以考虑在用户进行某些动作时执行该函数，默默保存当前编辑结果，而无需弹出对话框让用户确认。