在"文檔/視圖"架構的MFC程序中，提供了文檔模板管理者類CDocManager，由它管理應用程序所包含的文檔模板。我們先看看這個類的聲明：

/ // CDocTemplate manager object class CDocManager : public CObject {DECLARE_DYNAMIC(CDocManager)public:// ConstructorCDocManager();//Document functionsvirtual void AddDocTemplate(CDocTemplate* pTemplate);virtual POSITION GetFirstDocTemplatePosition() const;virtual CDocTemplate* GetNextDocTemplate(POSITION& pos) const;virtual void RegisterShellFileTypes(BOOL bCompat);void UnregisterShellFileTypes();virtual CDocument* OpenDocumentFile(LPCTSTR lpszFileName); // open named filevirtual BOOL SaveAllModified(); // save before exitvirtual void CloseAllDocuments(BOOL bEndSession); // close documents before exitingvirtual int GetOpenDocumentCount();// helper for standard commdlg dialogsvirtual BOOL DoPromptFileName(CString& fileName, UINT nIDSTitle,DWORD lFlags, BOOL bOpenFileDialog, CDocTemplate* pTemplate);//Commands// Advanced: process async DDE requestvirtual BOOL OnDDECommand(LPTSTR lpszCommand);virtual void OnFileNew();virtual void OnFileOpen();// Implementationprotected:CPtrList m_templateList;int GetDocumentCount(); // helper to count number of total documentspublic:static CPtrList* pStaticList; // for static CDocTemplate objectsstatic BOOL bStaticInit; // TRUE during static initializationstatic CDocManager* pStaticDocManager; // for static CDocTemplate objectspublic:virtual ~CDocManager();#ifdef _DEBUGvirtual void AssertValid() const;virtual void Dump(CDumpContext& dc) const;#endif };

從上述代碼可以看出，CDocManager類維護一個CPtrList類型的鏈表m_templateList（即文檔模板鏈表，實際上，MFC的設計者在MFC的實現中大量使用了鏈表這種數據結構），CPtrList類型定義為：

class CPtrList : public CObject {DECLARE_DYNAMIC(CPtrList)protected:struct CNode{CNode* pNext; CNode* pPrev;void* data;};public:// ConstructionCPtrList(int nBlockSize = 10);// Attributes (head and tail)// count of elementsint GetCount() const;BOOL IsEmpty() const;// peek at head or tailvoid*& 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 tailPOSITION AddHead(void* newElement);POSITION AddTail(void* newElement);// add another list of elements before head or after tailvoid AddHead(CPtrList* pNewList);void AddTail(CPtrList* pNewList);// remove all elementsvoid RemoveAll();// iterationPOSITION 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 positionvoid*& GetAt(POSITION position);void* GetAt(POSITION position) const;void SetAt(POSITION pos, void* newElement);void RemoveAt(POSITION position);// inserting before or after a given positionPOSITION 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 foundPOSITION FindIndex(int nIndex) const;// get the 'nIndex'th element (may return NULL)// Implementationprotected: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 _DEBUGvoid Dump(CDumpContext&) const;void AssertValid() const;#endif// local typedefs for class templatestypedef void* BASE_TYPE;typedef void* BASE_ARG_TYPE; };很顯然，CPtrList是對鏈表結構體
struct CNode
{
　CNode* pNext;?
　CNode* pPrev;
　void* data;
};
　　本身及其GetNext、GetPrev、GetAt、SetAt、RemoveAt、InsertBefore、InsertAfter、Find、FindIndex等各種操作的封裝。
　　作為一個抽象的鏈表類型，CPtrList并未定義其中節點的具體類型，而以一個void指針（struct CNode 中的void* data）巧妙地實現了鏈表節點成員具體類型的"模板"化。很顯然，在Visual C++6.0開發的年代，C++語言所具有的語法特征"模板"仍然沒有得到廣泛的應用。
而CDocManager類的成員函數
virtual void AddDocTemplate(CDocTemplate* pTemplate);
virtual POSITION GetFirstDocTemplatePosition() const;
virtual CDocTemplate* GetNextDocTemplate(POSITION& pos) const;

則完成對m_TemplateList鏈表的添加及遍歷操作的封裝，我們來看看這三個函數的源代碼：

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 listpTemplate->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.文檔模板類CDocTemplate

　　文檔模板類CDocTemplate是一個抽象基類（這意味著不能直接用它來定義對象而必須用它的派生類），它定義了文檔模板的基本處理函數接口。對一個單文檔界面程序，需使用單文檔模板類CSingleDocTemplate，而對于一個多文檔界面程序，需使用多文檔模板類CMultipleDocTemplate。我們首先來看看CDocTemplate類的聲明：?

class CDocTemplate : public CCmdTarget {DECLARE_DYNAMIC(CDocTemplate)// Constructorsprotected:CDocTemplate(UINT nIDResource, CRuntimeClass* pDocClass, CRuntimeClass* pFrameClass, CRuntimeClass* pViewClass);public:virtual void LoadTemplate();// Attributespublic:// setup for OLE containersvoid SetContainerInfo(UINT nIDOleInPlaceContainer);// setup for OLE serversvoid SetServerInfo(UINT nIDOleEmbedding, UINT nIDOleInPlaceServer = 0, CRuntimeClass* pOleFrameClass = NULL, CRuntimeClass* pOleViewClass = NULL);// iterating over open documentsvirtual POSITION GetFirstDocPosition() const = 0;virtual CDocument* GetNextDoc(POSITION& rPos) const = 0;// Operationspublic:virtual void AddDocument(CDocument* pDoc); // must overridevirtual void RemoveDocument(CDocument* pDoc); // must overrideenum DocStringIndex{windowTitle, // default window titledocName, // user visible name for default documentfileNewName, // user visible name for FileNew// for file based documents:filterName, // user visible name for FileOpenfilterExt, // user visible extension for FileOpen// for file based documents with Shell open support:regFileTypeId, // REGEDIT visible registered file type identifierregFileTypeName, // Shell visible registered file type name};virtual BOOL GetDocString(CString& rString, enum DocStringIndex index) const; // get one of the info stringsCFrameWnd* CreateOleFrame(CWnd* pParentWnd, CDocument* pDoc,BOOL bCreateView);// Overridablespublic:enum Confidence{noAttempt,maybeAttemptForeign,maybeAttemptNative,yesAttemptForeign,yesAttemptNative,yesAlreadyOpen};virtual Confidence MatchDocType(LPCTSTR lpszPathName,CDocument*& rpDocMatch);virtual CDocument* CreateNewDocument();virtual CFrameWnd* CreateNewFrame(CDocument* pDoc, CFrameWnd* pOther);virtual void InitialUpdateFrame(CFrameWnd* pFrame, CDocument* pDoc,BOOL bMakeVisible = TRUE);virtual BOOL SaveAllModified(); // for all documentsvirtual void CloseAllDocuments(BOOL bEndSession);virtual CDocument* OpenDocumentFile(LPCTSTR lpszPathName, BOOL bMakeVisible = TRUE) = 0;// open named file// if lpszPathName == NULL => create new file with this typevirtual void SetDefaultTitle(CDocument* pDocument) = 0;// Implementationpublic:BOOL m_bAutoDelete;virtual ~CDocTemplate();// back pointer to OLE or other server (NULL if none or disabled)CObject* m_pAttachedFactory;// menu & accelerator resources for in-place containerHMENU m_hMenuInPlace;HACCEL m_hAccelInPlace;// menu & accelerator resource for server editing embeddingHMENU m_hMenuEmbedding;HACCEL m_hAccelEmbedding;// menu & accelerator resource for server editing in-placeHMENU m_hMenuInPlaceServer;HACCEL m_hAccelInPlaceServer;#ifdef _DEBUGvirtual void Dump(CDumpContext&) const;virtual void AssertValid() const;#endifvirtual void OnIdle(); // for all documentsvirtual BOOL OnCmdMsg(UINT nID, int nCode, void* pExtra,AFX_CMDHANDLERINFO* pHandlerInfo);protected:UINT m_nIDResource; // IDR_ for frame/menu/accel as wellUINT m_nIDServerResource; // IDR_ for OLE inplace frame/menu/accelUINT m_nIDEmbeddingResource; // IDR_ for OLE open frame/menu/accelUINT m_nIDContainerResource; // IDR_ for container frame/menu/accelCRuntimeClass* m_pDocClass; // class for creating new documentsCRuntimeClass* m_pFrameClass; // class for creating new framesCRuntimeClass* m_pViewClass; // class for creating new viewsCRuntimeClass* m_pOleFrameClass; // class for creating in-place frameCRuntimeClass* m_pOleViewClass; // class for creating in-place viewCString m_strDocStrings; // '\n' separated names// The document names sub-strings are represented as _one_ string:// windowTitle\ndocName\n ... (see DocStringIndex enum) };

文檔模板掛接了后面要介紹的文檔、視圖和框架窗口，使得它們得以互相關聯。通過文檔模板，程序確定了創建或打開一個文檔時，以什么樣的視圖和框架窗口來顯示。文檔模板依靠保存相互對應的文檔、視圖和框架窗口的CRuntimeClass對象指針來實現上述掛接，這就是文檔模板類中的成員變量m_pDocClass、m_pFrameClass、m_pViewClass的由來。實際上，對m_pDocClass、m_pFrameClass、m_pViewClass的賦值在CDocTemplate類的構造函數中實施：

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 heapif (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 heapLoadTemplate();} }

文檔模板類CDocTemplate還保存了它所支持的全部文檔類的信息，包括所支持文檔的文件擴展名、文檔在框架窗口中的名字、圖標等。CDocTemplate類的AddDocument、RemoveDocument成員函數使得CDocument* pDoc參數所指向的文檔歸屬于本文檔模板（通過將this指針賦值給pDoc所指向CDocument對象的m_pDocTemplate成員變量）或脫離與本文檔模板的關系：

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

而CDocTemplate類的CreateNewDocument成員函數則首先調用CDocument運行時類的CreateObject函數創建一個CDocument對象，再調用AddDocument成員函數將其歸屬于本文檔模板類：

CDocument* CDocTemplate::CreateNewDocument() {// default implementation constructs one from CRuntimeClassif (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; }文檔類對象由文檔模板類構造生成，單文檔模板類CSingleDocTemplate只能生成一個文檔類對象，并用成員變量 m_pOnlyDoc 指向該對象；多文檔模板類可以生成多個文檔類對象，用成員變量 m_docList 指向文檔對象組成的鏈表。

　　CSingleDocTemplate的構造函數、AddDocument及RemoveDocument成員函數都在CDocTemplate類相應函數的基礎上增加了對m_pOnlyDoc指針的處理：

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 pleaseASSERT_VALID(pDoc);CDocTemplate::AddDocument(pDoc);m_pOnlyDoc = pDoc; } void CSingleDocTemplate::RemoveDocument(CDocument* pDoc) {ASSERT(m_pOnlyDoc == pDoc); // must be this oneASSERT_VALID(pDoc);CDocTemplate::RemoveDocument(pDoc);m_pOnlyDoc = NULL; }

同樣，CMultiDocTemplate類的相關函數也需要對m_docList所指向的鏈表進行操作（實際上AddDocument和RemoveDocument成員函數是文檔模板管理其所包含文檔的函數）：

// 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 listm_docList.AddTail(pDoc); } void CMultiDocTemplate::RemoveDocument(CDocument* pDoc) {ASSERT_VALID(pDoc);CDocTemplate::RemoveDocument(pDoc);m_docList.RemoveAt(m_docList.Find(pDoc)); }

由于CMultiDocTemplate類可包含多個文檔，依靠其成員函數GetFirstDocPosition和GetNextDoc完成對文檔鏈表m_docList的遍歷：

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

而CSingleDocTemplate的這兩個函數實際上并無太大的意義，僅僅是MFC要玩的某種"招數"，這個"招數"高明嗎？相信看完MFC的相關源代碼后你或許不會這么認為，實際上CSingleDocTemplate的GetFirstDocPosition、GetNextDoc函數僅僅只能判斷m_pOnlyDoc的是否為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 documentASSERT(m_pOnlyDoc != NULL);pDoc = m_pOnlyDoc;}rPos = NULL; // no morereturn pDoc; }

筆者認為，MFC的設計者們將GetFirstDocPosition、GetNextDoc作為基類CDocTemplate的成員函數是不合理的，一種更好的做法是將GetFirstDocPosition、GetNextDoc移至CMultiDocTemplate派生類。

CDocTemplate還需完成對其對應文檔的關閉與保存操作：

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();} }前文我們提到，由于MFC的設計者將CSingleDocTemplate和CMultiDocTemplate的行為未進行規范的區分，它對僅僅對應一個文檔的CSingleDocTemplate也提供了所謂的GetFirstDocPosition、GetNextDoc遍歷操作，所以基類CDocTemplate的SaveAllModified和CloseAllDocuments函數（都是遍歷）就可統一CSingleDocTemplate和CMultiDocTemplate兩個本身并不相同類的SaveAllModified和CloseAllDocuments行為（實際上，對于CSingleDocTemplate而言，SaveAllModified和CloseAllDocuments中的"All"是沒有太大意義的。教室里有1個老師和N個同學，老師可以對同學們說"所有同學"，而學生對老師說"所有老師"相信會被當成神經病）。MFC的設計者們特意使用了"將錯就錯"的方法意圖簡化CSingleDocTemplate和CMultiDocTemplate類的設計，讀者朋友可以不認同他們的做法。

　　CDocTemplate還提供了框架窗口的創建和初始化函數：

/ // Default frame creation CFrameWnd* CDocTemplate::CreateNewFrame(CDocument* pDoc, CFrameWnd* pOther) {if (pDoc != NULL)ASSERT_VALID(pDoc);// create a frame wired to the specified documentASSERT(m_nIDResource != 0); // must have a resource ID to load fromCCreateContext 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 resourceif (!pFrame->LoadFrame(m_nIDResource,WS_OVERLAPPEDWINDOW | FWS_ADDTOTITLE, // default frame styles NULL, &context)){TRACE0("Warning: CDocTemplate couldn't create a frame.\n");// frame will be deleted in PostNcDestroy cleanupreturn NULL;}// it worked !return pFrame; } void CDocTemplate::InitialUpdateFrame(CFrameWnd* pFrame, CDocument* pDoc,BOOL bMakeVisible) {// just delagate to implementation in CFrameWndpFrame->InitialUpdateFrame(pDoc, bMakeVisible); }3. CWinApp與CDocManager/CDocTemplate類

　　應用程序CWinApp類對象與CDocManager和CDocTemplate類的關系是：CWinApp對象中包含一個CDocManager指針類型的共有數據成員m_pDocManager，CWinApp::InitInstance函數調用CWinApp::AddDocTemplate函數向鏈表m_templateList添加模板指針(實際上是調用前文所述CDocManager的AddDocTemplate函數)。另外，CWinApp也提供了GetFirstDocTemplatePosition和GetNextDocTemplate函數實現來對m_templateList鏈表進行訪問（實際上也是調用了前文所述CDocManager的GetFirstDocTemplatePosition、GetNextDocTemplate函數）。我們僅摘取CWinApp類聲明的一小部分：

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

來看CWinApp派生類CSDIExampleApp（單文檔）、CMDIExampleApp（多文檔）的InitInstance成員函數的例子（僅僅摘取與文檔模板相關的部分）：

BOOL CSDIExampleApp::InitInstance() {…CSingleDocTemplate* pDocTemplate;pDocTemplate = new CSingleDocTemplate(IDR_MAINFRAME,RUNTIME_CLASS(CSDIExampleDoc), RUNTIME_CLASS(CMainFrame), // main SDI frame window RUNTIME_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 frameRUNTIME_CLASS(CMDIExampleView));AddDocTemplate(pDocTemplate);… }讀者朋友，看完本次連載，也許您有許多不明白的地方，這是正常的。因為其所講解的內容與后續幾次連載息息相關，我們愈往后看，就會愈加清晰。對于本次連載的內容，您只需要建立基本的印象。最初的淺嘗輒止是為了最終的深入脊髓！


　　我們試圖對MFC的深層機理刨根究底，"撥開云霧見月明"的過程是艱辛的！

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