深入浅出MFC文档/视图架构之文档模板

文档模板管理者类CDocManager

　　在"文档/视图"架构的MFC程序中，提供了文档模板管理者类CDocManager，由它管理应用程序所包含的文档模板。我们先看看这个类的声明：

 

class CPtrList : public CObject{　DECLARE_DYNAMIC(CPtrList)　protected:　　struct CNode　　{　　　CNode* pNext; 　　　CNode* pPrev;　　　void* data;　　};　public:　　// Construction　　CPtrList(int nBlockSize = 10);　　// Attributes (head and tail)　　// count of elements　　int GetCount() const;　　BOOL IsEmpty() const;　　// peek at head or tail　　void*& GetHead();　　void* GetHead() const;　　void*& GetTail();　　void* GetTail() const;　　// Operations　　// get head or tail (and remove it) - don't call on empty list!　　void* RemoveHead();　　void* RemoveTail();　　// add before head or after tail　　POSITION AddHead(void* newElement);　　POSITION AddTail(void* newElement);　　// add another list of elements before head or after tail　　void AddHead(CPtrList* pNewList);　　void AddTail(CPtrList* pNewList);　　// remove all elements　　void RemoveAll();　　// iteration　　POSITION GetHeadPosition() const;　　POSITION GetTailPosition() const;　　void*& GetNext(POSITION& rPosition); // return *Position++　　void* GetNext(POSITION& rPosition) const; // return *Position++　　void*& GetPrev(POSITION& rPosition); // return *Position--　　void* GetPrev(POSITION& rPosition) const; // return *Position--　　// getting/modifying an element at a given position　　void*& GetAt(POSITION position);　　void* GetAt(POSITION position) const;　　void SetAt(POSITION pos, void* newElement);　　void RemoveAt(POSITION position);　　// inserting before or after a given position　　POSITION InsertBefore(POSITION position, void* newElement);　　POSITION InsertAfter(POSITION position, void* newElement);　　// helper functions (note: O(n) speed)　　POSITION Find(void* searchValue, POSITION startAfter = NULL) const;　　// defaults to starting at the HEAD　　// return NULL if not found　　POSITION FindIndex(int nIndex) const;　　// get the 'nIndex'th element (may return NULL)　　// Implementation　protected:　　CNode* m_pNodeHead;　　CNode* m_pNodeTail;　　int m_nCount;　　CNode* m_pNodeFree;　　struct CPlex* m_pBlocks;　　int m_nBlockSize;　　CNode* NewNode(CNode*, CNode*);　　void FreeNode(CNode*);　public:　　~CPtrList();　　#ifdef _DEBUG　　　void Dump(CDumpContext&) const;　　　void AssertValid() const;　　#endif　　// local typedefs for class templates　　typedef void* BASE_TYPE;　　typedef void* BASE_ARG_TYPE;};很显然，CPtrList是对链表结构体struct CNode{　CNode* pNext; 　CNode* pPrev;　void* data;};

 本身及其GetNext、GetPrev、GetAt、SetAt、RemoveAt、InsertBefore、InsertAfter、Find、FindIndex等各种操作的封装。

　　作为一个抽象的链表类型，CPtrList并未定义其中节点的具体类型，而以一个void指针（struct CNode 中的void* data）巧妙地实现了链表节点成员具体类型的"模板"化。很显然，在Visual C++6.0开发的年代，C++语言所具有的语法特征"模板"仍然没有得到广泛的应用。
而CDocManager类的成员函数

virtual void AddDocTemplate(CDocTemplate* pTemplate);virtual POSITION GetFirstDocTemplatePosition() const;virtual CDocTemplate* GetNextDocTemplate(POSITION& pos) const; 

则完成对m_TemplateList链表的添加及遍历操作的封装，我们来看看这三个函数的源代码：

void CDocManager::AddDocTemplate(CDocTemplate* pTemplate){　if (pTemplate == NULL)　{　　if (pStaticList != NULL)　　{　　　POSITION pos = pStaticList->GetHeadPosition();　　　while (pos != NULL)　　　{　　　　CDocTemplate* pTemplate = (CDocTemplate*)pStaticList->GetNext(pos);　　　　AddDocTemplate(pTemplate);　　　}　　　delete pStaticList;　　　pStaticList = NULL;　　}　　bStaticInit = FALSE;　}　else　{　　ASSERT_VALID(pTemplate);　　ASSERT(m_templateList.Find(pTemplate, NULL) == NULL);// must not be in list　　pTemplate->LoadTemplate();　　m_templateList.AddTail(pTemplate);　}}POSITION CDocManager::GetFirstDocTemplatePosition() const{　return m_templateList.GetHeadPosition();}CDocTemplate* CDocManager::GetNextDocTemplate(POSITION& pos) const{　return (CDocTemplate*)m_templateList.GetNext(pos);}

2.文档模板类CDocTemplate

　　文档模板类CDocTemplate是一个抽象基类（这意味着不能直接用它来定义对象而必须用它的派生类），它定义了文档模板的基本处理函数接口。对一个单文档界面程序，需使用单文档模板类CSingleDocTemplate，而对于一个多文档界面程序，需使用多文档模板类CMultipleDocTemplate。我们首先来看看CDocTemplate类的声明：

 

CDocTemplate::CDocTemplate(UINT nIDResource, CRuntimeClass* pDocClass,CRuntimeClass* pFrameClass, CRuntimeClass* pViewClass){　ASSERT_VALID_IDR(nIDResource);　ASSERT(pDocClass == NULL || pDocClass->IsDerivedFrom(RUNTIME_CLASS(CDocument)));　ASSERT(pFrameClass == NULL ||pFrameClass->IsDerivedFrom(RUNTIME_CLASS(CFrameWnd)));　ASSERT(pViewClass == NULL || pViewClass->IsDerivedFrom(RUNTIME_CLASS(CView)));　m_nIDResource = nIDResource;　m_nIDServerResource = NULL;　m_nIDEmbeddingResource = NULL;　m_nIDContainerResource = NULL;　m_pDocClass = pDocClass;　m_pFrameClass = pFrameClass;　m_pViewClass = pViewClass;　m_pOleFrameClass = NULL;　m_pOleViewClass = NULL;　m_pAttachedFactory = NULL;　m_hMenuInPlace = NULL;　m_hAccelInPlace = NULL;　m_hMenuEmbedding = NULL;　m_hAccelEmbedding = NULL;　m_hMenuInPlaceServer = NULL;　m_hAccelInPlaceServer = NULL;　// add to pStaticList if constructed as static instead of on heap　if (CDocManager::bStaticInit)　{　　m_bAutoDelete = FALSE;　　if (CDocManager::pStaticList == NULL)　　　CDocManager::pStaticList = new CPtrList;　　if (CDocManager::pStaticDocManager == NULL)　　　CDocManager::pStaticDocManager = new CDocManager;　　　CDocManager::pStaticList->AddTail(this);　}　else　{　　m_bAutoDelete = TRUE; // usually allocated on the heap　　LoadTemplate();　}}

 文档模板类CDocTemplate还保存了它所支持的全部文档类的信息，包括所支持文档的文件扩展名、文档在框架窗口中的名字、图标等。

CDocTemplate类的AddDocument、RemoveDocument成员函数使得CDocument* pDoc参数所指向的文档归属于本文档模板（通过将this指针赋值给pDoc所指向CDocument对象的m_pDocTemplate成员变量）或脱离与本文档模板的关系：

void CDocTemplate::AddDocument(CDocument* pDoc){　ASSERT_VALID(pDoc);　ASSERT(pDoc->m_pDocTemplate == NULL); // no template attached yet　pDoc->m_pDocTemplate = this;}void CDocTemplate::RemoveDocument(CDocument* pDoc){　ASSERT_VALID(pDoc);　ASSERT(pDoc->m_pDocTemplate == this); // must be attached to us　pDoc->m_pDocTemplate = NULL;}

而CDocTemplate类的CreateNewDocument成员函数则首先调用CDocument运行时类的CreateObject函数创建一个CDocument对象，再调用AddDocument成员函数将其归属于本文档模板类：

CDocument* CDocTemplate::CreateNewDocument(){　// default implementation constructs one from CRuntimeClass　if (m_pDocClass == NULL)　{　　TRACE0("Error: you must override CDocTemplate::CreateNewDocument./n");　　ASSERT(FALSE);　　return NULL;　}　CDocument* pDocument = (CDocument*)m_pDocClass->CreateObject();　if (pDocument == NULL)　{　　TRACE1("Warning: Dynamic create of document type %hs failed./n",m_pDocClass->m_lpszClassName);　　return NULL;　}　ASSERT_KINDOF(CDocument, pDocument);　AddDocument(pDocument);　return pDocument;}

文档类对象由文档模板类构造生成，单文档模板类CSingleDocTemplate只能生成一个文档类对象，并用成员变量 m_pOnlyDoc 指向该对象；多文档模板类可以生成多个文档类对象，用成员变量 m_docList 指向文档对象组成的链表。

　　CSingleDocTemplate的构造函数、AddDocument及RemoveDocument成员函数都在CDocTemplate类相应函数的基础上增加了对m_pOnlyDoc指针的处理：

CSingleDocTemplate::CSingleDocTemplate(UINT nIDResource,CRuntimeClass* pDocClass, CRuntimeClass* pFrameClass,CRuntimeClass* pViewClass): CDocTemplate(nIDResource, pDocClass, pFrameClass, pViewClass){　m_pOnlyDoc = NULL;}void CSingleDocTemplate::AddDocument(CDocument* pDoc){　ASSERT(m_pOnlyDoc == NULL); // one at a time please　ASSERT_VALID(pDoc);　CDocTemplate::AddDocument(pDoc);　m_pOnlyDoc = pDoc;}void CSingleDocTemplate::RemoveDocument(CDocument* pDoc){　ASSERT(m_pOnlyDoc == pDoc); // must be this one　ASSERT_VALID(pDoc);　CDocTemplate::RemoveDocument(pDoc);　m_pOnlyDoc = NULL;}

同样，CMultiDocTemplate类的相关函数也需要对m_docList所指向的链表进行操作（实际上AddDocument和RemoveDocument成员函数是文档模板管理其所包含文档的函数）：

// CMultiDocTemplate document management (a list of currently open documents)void CMultiDocTemplate::AddDocument(CDocument* pDoc){　ASSERT_VALID(pDoc);　CDocTemplate::AddDocument(pDoc);　ASSERT(m_docList.Find(pDoc, NULL) == NULL); // must not be in list　m_docList.AddTail(pDoc);}void CMultiDocTemplate::RemoveDocument(CDocument* pDoc){　ASSERT_VALID(pDoc);　CDocTemplate::RemoveDocument(pDoc);　m_docList.RemoveAt(m_docList.Find(pDoc));}

由于CMultiDocTemplate类可包含多个文档，依靠其成员函数GetFirstDocPosition和GetNextDoc完成对文档链表m_docList的遍历：

POSITION CMultiDocTemplate::GetFirstDocPosition() const{　return m_docList.GetHeadPosition();}CDocument* CMultiDocTemplate::GetNextDoc(POSITION& rPos) const{　return (CDocument*)m_docList.GetNext(rPos);}

而CSingleDocTemplate的这两个函数实际上并无太大的意义，仅仅是MFC要玩的某种"招数"，这个"招数"高明吗？相信看完MFC的相关源代码后你或许不会这么认为，实际上CSingleDocTemplate的GetFirstDocPosition、GetNextDoc函数仅仅只能判断m_pOnlyDoc的是否为NULL：

POSITION CSingleDocTemplate::GetFirstDocPosition() const{　return (m_pOnlyDoc == NULL) ? NULL : BEFORE_START_POSITION;}CDocument* CSingleDocTemplate::GetNextDoc(POSITION& rPos) const{　CDocument* pDoc = NULL;　if (rPos == BEFORE_START_POSITION)　{　　// first time through, return a real document　　ASSERT(m_pOnlyDoc != NULL);　　pDoc = m_pOnlyDoc;　}　rPos = NULL; // no more　return pDoc;}

笔者认为，MFC的设计者们将GetFirstDocPosition、GetNextDoc作为基类CDocTemplate的成员函数是不合理的，一种更好的做法是将GetFirstDocPosition、GetNextDoc移至CMultiDocTemplate派生类。
　　CDocTemplate还需完成对其对应文档的关闭与保存操作

BOOL CDocTemplate::SaveAllModified(){　POSITION pos = GetFirstDocPosition();　while (pos != NULL)　{　　CDocument* pDoc = GetNextDoc(pos);　　if (!pDoc->SaveModified())　　　return FALSE;　}　return TRUE;}void CDocTemplate::CloseAllDocuments(BOOL){　POSITION pos = GetFirstDocPosition();　while (pos != NULL)　{　　CDocument* pDoc = GetNextDoc(pos);　　pDoc->OnCloseDocument();　}} 

        前文我们提到，由于MFC的设计者将CSingleDocTemplate和CMultiDocTemplate的行为未进行规范的区分，它对仅仅对应一个文档的CSingleDocTemplate也提供了所谓的GetFirstDocPosition、GetNextDoc遍历操作，所以基类CDocTemplate的SaveAllModified和CloseAllDocuments函数（都是遍历）就可统一CSingleDocTemplate和CMultiDocTemplate两个本身并不相同类的SaveAllModified和CloseAllDocuments行为（实际上，对于CSingleDocTemplate而言，SaveAllModified和CloseAllDocuments中的"All"是没有太大意义的。教室里有1个老师和N个同学，老师可以对同学们说"所有同学"，而学生对老师说"所有老师"相信会被当成神经病）。MFC的设计者们特意使用了"将错就错"的方法意图简化CSingleDocTemplate和CMultiDocTemplate类的设计，读者朋友可以不认同他们的做法。
　　CDocTemplate还提供了框架窗口的创建和初始化函数：

/////////////////////////////////////////////////////////////////////////////// Default frame creationCFrameWnd* CDocTemplate::CreateNewFrame(CDocument* pDoc, CFrameWnd* pOther){　if (pDoc != NULL)　　ASSERT_VALID(pDoc);　　// create a frame wired to the specified document　ASSERT(m_nIDResource != 0); // must have a resource ID to load from　CCreateContext context;　context.m_pCurrentFrame = pOther;　context.m_pCurrentDoc = pDoc;　context.m_pNewViewClass = m_pViewClass;　context.m_pNewDocTemplate = this;　if (m_pFrameClass == NULL)　{　　TRACE0("Error: you must override CDocTemplate::CreateNewFrame./n");　　ASSERT(FALSE);　　return NULL;　}　CFrameWnd* pFrame = (CFrameWnd*)m_pFrameClass->CreateObject();　if (pFrame == NULL)　{　　TRACE1("Warning: Dynamic create of frame %hs failed./n",m_pFrameClass->m_lpszClassName);　　return NULL;　}　ASSERT_KINDOF(CFrameWnd, pFrame);　if (context.m_pNewViewClass == NULL)　　TRACE0("Warning: creating frame with no default view./n");　// create new from resource　if (!pFrame->LoadFrame(m_nIDResource,WS_OVERLAPPEDWINDOW | FWS_ADDTOTITLE, // default frame stylesNULL, &context))　{　　TRACE0("Warning: CDocTemplate couldn't create a frame./n");　　// frame will be deleted in PostNcDestroy cleanup　　return NULL;　}　// it worked !　return pFrame;}void CDocTemplate::InitialUpdateFrame(CFrameWnd* pFrame, CDocument* pDoc,BOOL bMakeVisible){　// just delagate to implementation in CFrameWnd　pFrame->InitialUpdateFrame(pDoc, bMakeVisible);} 

3. CWinApp与CDocManager/CDocTemplate类
　　应用程序CWinApp类对象与CDocManager和CDocTemplate类的关系是：CWinApp对象中包含一个CDocManager指针类型的共有数据成员m_pDocManager，CWinApp::InitInstance函数调用CWinApp::AddDocTemplate函数向链表m_templateList添加模板指针(实际上是调用前文所述CDocManager的AddDocTemplate函数)。另外，CWinApp也提供了GetFirstDocTemplatePosition和GetNextDocTemplate函数实现来对m_templateList链表进行访问（实际上也是调用了前文所述CDocManager的GetFirstDocTemplatePosition、GetNextDocTemplate函数）。我们仅摘取CWinApp类声明的一小部分：

class CWinApp : public CWinThread{　…　CDocManager* m_pDocManager;　// Running Operations - to be done on a running application　// Dealing with document templates　void AddDocTemplate(CDocTemplate* pTemplate);　POSITION GetFirstDocTemplatePosition() const;　CDocTemplate* GetNextDocTemplate(POSITION& pos) const;　// Dealing with files　virtual CDocument* OpenDocumentFile(LPCTSTR lpszFileName); // open named file　void CloseAllDocuments(BOOL bEndSession); // close documents before exiting　// Command Handlersprotected:　// map to the following for file new/open　afx_msg void OnFileNew();　afx_msg void OnFileOpen();　int GetOpenDocumentCount();　…}; 

来看CWinApp派生类CSDIExampleApp（单文档）、CMDIExampleApp（多文档）的InitInstance成员函数的例子（仅仅摘取与文档模板相关的部分）：

BOOL CSDIExampleApp::InitInstance(){　…　CSingleDocTemplate* pDocTemplate;　pDocTemplate = new CSingleDocTemplate(IDR_MAINFRAME,RUNTIME_CLASS(CSDIExampleDoc),RUNTIME_CLASS(CMainFrame), // main SDI frame windowRUNTIME_CLASS(CSDIExampleView));　AddDocTemplate(pDocTemplate);　…　return TRUE;}BOOL CMDIExampleApp::InitInstance(){　…　CMultiDocTemplate* pDocTemplate;　pDocTemplate = new CMultiDocTemplate(IDR_MDIEXATYPE,　　RUNTIME_CLASS(CMDIExampleDoc),　　RUNTIME_CLASS(CChildFrame), // custom MDI child frame　　RUNTIME_CLASS(CMDIExampleView));　　AddDocTemplate(pDocTemplate);　…}