版本：Visual Studio 6.0 + Service Pack 5 下的MFC6

文档类：CRichEditDoc的派生类

视图类：包括CRichEditView派生类及非CRichEditView派生类在内的多个视图

问题：程序在关闭文档时出错。

分析：

在CDocument里
void CDocument::OnCloseDocument()
{
        while (!m_viewList.IsEmpty())
        {
                // get frame attached to the view
                CView* pView = (CView*)m_viewList.GetHead();
                ASSERT_VALID(pView);
                CFrameWnd* pFrame = pView->GetParentFrame();
                ASSERT_VALID(pFrame);
                // and close it
                PreCloseFrame(pFrame);
                pFrame->DestroyWindow();
                        // will destroy the view as well
        }
        ......
}
在CRichEditDoc里
CRichEditView* CRichEditDoc::GetView() const
{
        POSITION pos = GetFirstViewPosition();
        if (pos == NULL)
                return NULL;
        // find the first view that is a CRichEditView
        CView* pView;
        while (pos != NULL)
        {
                pView = GetNextView(pos);
                if (pView->IsKindOf(RUNTIME_CLASS(CRichEditView)))
                        return (CRichEditView*) pView;
        }
        // can't find one--return NULL
        return NULL;
}
void CRichEditDoc::PreCloseFrame(CFrameWnd* pFrameArg)
{
        ......
        // deactivate any inplace active items on this frame
        GetView()->m_lpRichEditOle->InPlaceDeactivate();   ................................................................1
        ......
}

可以发现，CDocument::OnCloseDocument在关闭每一个视图的时候总会调用PreCloseFrame来处理一些善后的工作，而CRichEditDoc::PreCloseFrame总调用CRichEditDoc::GetView() 来获得这些视图类的指针，但是CRichEditDoc::GetView() 只返回类型为CRichEditView派生类的视图对象的指针，这就造成CRichEditDoc::GetView() 在遇到非CRichEditView派生类的视图对象时候只是返回一个NULL，于是在1处程序出错，所以在这种情况下我们必须在CDocument::OnCloseDocument被调用之前手动关闭掉所有与CRichEditDoc相关联的非CRichEditView的派生类的视图。

我不知到这是不是微软特意这样做，总之在往CRichEditDoc里添加View后，关闭的
时候都要先手动关闭其他不是CRichEditView派生出来的View,不知各位有什么见解
^_^