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：
/// CDocTemplate manager object class CDocManager : public CObject{ DECLARE_DYNAMIC(CDocManager) public: // Constructor CDocManager(); //Document functions virtual 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 file virtual BOOL SaveAllModified(); // save before exit virtual void CloseAllDocuments(BOOL bEndSession); // close documents before exiting virtual int GetOpenDocumentCount(); // helper for standard commdlg dialogs virtual BOOL DoPromptFileName(CString& fileName, UINT nIDSTitle, DWORD lFlags, BOOL bOpenFileDialog, CDocTemplate* pTemplate); //Commands // Advanced: process async DDE request virtual BOOL OnDDECommand(LPTSTR lpszCommand); virtual void OnFileNew(); virtual void OnFileOpen(); // Implementation protected: CPtrList m_templateList; int GetDocumentCount(); // helper to count number of total documents public: static CPtrList* pStaticList; // for static CDocTemplate objects static BOOL bStaticInit; // TRUE during static initialization static CDocManager* pStaticDocManager; // for static CDocTemplate objects public: virtual ~CDocManager(); #ifdef _DEBUG virtual void AssertValid() const; virtual void Dump(CDumpContext& dc) const; #endif};
从上述代码可以看出，CDocManager类维护一个CPtrList类型的链表m_templateList（即文档模板链表，实际上，MFC的设计者在MFC的实现中大量使用了链表这种数据结构），CPtrList类型定义为：
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) - dont 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 nIndexth 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：
class CDocTemplate : public CCmdTarget{ DECLARE_DYNAMIC(CDocTemplate) // Constructors protected: CDocTemplate(UINT nIDResource, CRuntimeClass* pDocClass, CRuntimeClass* pFrameClass, CRuntimeClass* pViewClass); public: virtual void LoadTemplate(); // Attributes public: // setup for OLE containers void SetContainerInfo(UINT nIDOleInPlaceContainer); // setup for OLE servers void SetServerInfo(UINT nIDOleEmbedding, UINT nIDOleInPlaceServer = 0,CRuntimeClass* pOleFrameClass = NULL, CRuntimeClass* pOleViewClass = NULL); // iterating over open documents virtual POSITION GetFirstDocPosition() const = 0; virtual CDocument* GetNextDoc(POSITION& rPos) const = 0; // Operations public: virtual void AddDocument(CDocument* pDoc); // must override virtual void RemoveDocument(CDocument* pDoc); // must override enum DocStringIndex { windowTitle, // default window title docName, // user visible name for default document fileNewName, // user visible name for FileNew // for file based documents: filterName, // user visible name for FileOpen filterExt, // user visible extension for FileOpen // for file based documents with Shell open support: regFileTypeId, // REGEDIT visible registered file type identifier regFileTypeName, // Shell visible registered file type name }; virtual BOOL GetDocString(CString& rString,enum DocStringIndex index) const; // get one of the info strings CFrameWnd* CreateOleFrame(CWnd* pParentWnd, CDocument* pDoc,BOOL bCreateView); // Overridables public: 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 documents virtual void CloseAllDocuments(BOOL bEndSession); virtual CDocument* OpenDocumentFile( LPCTSTR lpszPathName, BOOL bMakeVisible = TRUE) = 0; // open named file // if lpszPathName == NULL => create new file with this type virtual void SetDefaultTitle(CDocument* pDocument) = 0; // Implementation public: 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 container HMENU m_hMenuInPlace; HACCEL m_hAccelInPlace; // menu & accelerator resource for server editing embedding HMENU m_hMenuEmbedding; HACCEL m_hAccelEmbedding; // menu & accelerator resource for server editing in-place HMENU m_hMenuInPlaceServer; HACCEL m_hAccelInPlaceServer; #ifdef _DEBUG virtual void Dump(CDumpContext&) const; virtual void AssertValid() const; #endif virtual void OnIdle(); // for all documents virtual BOOL OnCmdMsg(UINT nID, int nCode, void* pExtra,AFX_CMDHANDLERINFO* pHandlerInfo); protected: UINT m_nIDResource; // IDR_ for frame/menu/accel as well UINT m_nIDServerResource; // IDR_ for OLE inplace frame/menu/accel UINT m_nIDEmbeddingResource; // IDR_ for OLE open frame/menu/accel UINT m_nIDContainerResource; // IDR_ for container frame/menu/accel CRuntimeClass* m_pDocClass; // class for creating new documents CRuntimeClass* m_pFrameClass; // class for creating new frames CRuntimeClass* m_pViewClass; // class for creating new views CRuntimeClass* m_pOleFrameClass; // class for creating in-place frame CRuntimeClass* m_pOleViewClass; // class for creating in-place view CString m_strDocStrings; // separated names // The document names sub-strings are represented as _one_ string: // windowTitle docName ... (see DocStringIndex enum)};
文档模板挂接了后面要介绍的文档、视图和框架窗口，使得它们得以互相关联。通过文档模板，程序确定了创建或打开一个文档时，以什么样的视图和框架窗口来显示。文档模板依靠保存相互对应的文档、视图和框架窗口的CRuntimeClass对象指针来实现上述挂接，这就是文档模板类中的成员变量m_pDocClass、m_pFrameClass、m_pViewClass的由来。实际上，对m_pDocClass、m_pFrameClass、m_pViewClass的赋值在CDocTemplate类的构造函数中实施：
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 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. "); ASSERT(FALSE); return NULL; } CDocument* pDocument = (CDocument*)m_pDocClass->CreateObject(); if (pDocument == NULL) { TRACE1("Warning: Dynamic create of document type %hs failed. ",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. "); ASSERT(FALSE); return NULL; } CFrameWnd* pFrame = (CFrameWnd*)m_pFrameClass->CreateObject(); if (pFrame == NULL) { TRACE1("Warning: Dynamic create of frame %hs failed. ",m_pFrameClass->m_lpszClassName); return NULL; } ASSERT_KINDOF(CFrameWnd, pFrame); if (context.m_pNewViewClass == NULL) TRACE0("Warning: creating frame with no default view. "); // create new from resource if (!pFrame->LoadFrame(m_nIDResource,WS_OVERLAPPEDWINDOW | FWS_ADDTOTITLE, // default frame stylesNULL, &context)) { TRACE0("Warning: CDocTemplate couldnt create a frame. "); // 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); …}
读者朋友，看完本次连载，也许您有许多不明白的地方，这是正常的。因为其所讲解的内容与后续几次连载息息相关，我们愈往后看，就会愈加清晰。对于本次连载的内容，您只需要建立基本的印象。最初的浅尝辄止是为了最终的深入脊髓！
我们试图对MFC的深层机理刨根究底，"拨开云雾见月明"的过程是艰辛的！
