Document/View的初始化过程

最近正在看《mfc深入浅出》，看到第8章Document/View深入探讨时候，对Document/View的建立过程不是很清楚，于是下大力气猛啃书和各种百度，明白了一些，做个小结：

先从CTest_DrawRectApp::InitInstance()开始

Test_DrawRect.cpp(这个文件是我建立名为Test_DrawRect工程自动生成的文件)

CSingleDocTemplate* pDocTemplate;
	pDocTemplate = new CSingleDocTemplate(
		IDR_MAINFRAME,
		RUNTIME_CLASS(CTest_DrawRectDoc),
		RUNTIME_CLASS(CMainFrame),       // 主 SDI 框架窗口
		RUNTIME_CLASS(CTest_DrawRectView));
	if (!pDocTemplate)
		return FALSE;
	AddDocTemplate(pDocTemplate);

afxwin.h

class CSingleDocTemplate : public CDocTemplate

class AFX_NOVTABLE CDocTemplate : public CCmdTarget
{
	DECLARE_DYNAMIC(CDocTemplate)		
	......
virtual CDocument* CreateNewDocument();
virtual CFrameWnd* CreateNewFrame(CDocument* pDoc, CFrameWnd* pOther);
	......
}

doctempl.cpp

CDocument* CDocTemplate::CreateNewDocument()
{
	// default implementation constructs one from CRuntimeClass
	if (m_pDocClass == NULL)
	{
		TRACE(traceAppMsg, 0, "Error: you must override CDocTemplate::CreateNewDocument.\n");
		ASSERT(FALSE);
		return NULL;
	}
	CDocument* pDocument = (CDocument*)m_pDocClass->CreateObject();
	if (pDocument == NULL)
	{
		TRACE(traceAppMsg, 0, "Warning: Dynamic create of document type %hs failed.\n",
			m_pDocClass->m_lpszClassName);
		return NULL;
	}
	ASSERT_KINDOF(CDocument, pDocument);
	AddDocument(pDocument);
	return pDocument;
}

/////////////////////////////////////////////////////////////////////////////
// Default frame creation

CFrameWnd* 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)
	{
		TRACE(traceAppMsg, 0, "Error: you must override CDocTemplate::CreateNewFrame.\n");
		ASSERT(FALSE);
		return NULL;
	}
	CFrameWnd* pFrame = (CFrameWnd*)m_pFrameClass->CreateObject();
	if (pFrame == NULL)
	{
		TRACE(traceAppMsg, 0, "Warning: Dynamic create of frame %hs failed.\n",
			m_pFrameClass->m_lpszClassName);
		return NULL;
	}
	ASSERT_KINDOF(CFrameWnd, pFrame);

	if (context.m_pNewViewClass == NULL)
		TRACE(traceAppMsg, 0, "Warning: creating frame with no default view.\n");

	// create new from resource
	if (!pFrame->LoadFrame(m_nIDResource,
			WS_OVERLAPPEDWINDOW | FWS_ADDTOTITLE,   // default frame styles
			NULL, &context))
	{
		TRACE(traceAppMsg, 0, "Warning: CDocTemplate couldn't create a frame.\n");
		// frame will be deleted in PostNcDestroy cleanup
		return NULL;
	}

	// it worked !
	return pFrame;
}

上面的意思就是DocTemplate这个类管理CDocument、CFrameWnd、CView这三个对象，在CDocTemplate类里有创建CFrameWnd、CDocument这两个对象的函数。那么CView对象在哪里生成呢？

在CFrameWnd里生成。

BOOL CFrameWnd::Create(LPCTSTR lpszClassName,
	LPCTSTR lpszWindowName,
	DWORD dwStyle,
	const RECT& rect,
	CWnd* pParentWnd,
	LPCTSTR lpszMenuName,
	DWORD dwExStyle,
	CCreateContext* pContext)
{
	HMENU hMenu = NULL;
	if (lpszMenuName != NULL)
	{
		// load in a menu that will get destroyed when window gets destroyed
		HINSTANCE hInst = AfxFindResourceHandle(lpszMenuName, ATL_RT_MENU);
		if ((hMenu = ::LoadMenu(hInst, lpszMenuName)) == NULL)
		{
			TRACE(traceAppMsg, 0, "Warning: failed to load menu for CFrameWnd.\n");
			PostNcDestroy();            // perhaps delete the C++ object
			return FALSE;
		}
	}

	m_strTitle = lpszWindowName;    // save title for later

	if (!CreateEx(dwExStyle, lpszClassName, lpszWindowName, dwStyle,
		rect.left, rect.top, rect.right - rect.left, rect.bottom - rect.top,
		pParentWnd->GetSafeHwnd(), hMenu, (LPVOID)pContext))
	{
		TRACE(traceAppMsg, 0, "Warning: failed to create CFrameWnd.\n");
		if (hMenu != NULL)
			DestroyMenu(hMenu);
		return FALSE;
	}

	return TRUE;
}

CWnd* CFrameWnd::CreateView(CCreateContext* pContext, UINT nID)
{
	ASSERT(m_hWnd != NULL);
	ASSERT(::IsWindow(m_hWnd));
	ENSURE_ARG(pContext != NULL);
	ENSURE_ARG(pContext->m_pNewViewClass != NULL);

	// Note: can be a CWnd with PostNcDestroy self cleanup
	CWnd* pView = (CWnd*)pContext->m_pNewViewClass->CreateObject();
	if (pView == NULL)
	{
		TRACE(traceAppMsg, 0, "Warning: Dynamic create of view type %hs failed.\n",
			pContext->m_pNewViewClass->m_lpszClassName);
		return NULL;
	}
	ASSERT_KINDOF(CWnd, pView);

	// views are always created with a border!
	if (!pView->Create(NULL, NULL, AFX_WS_DEFAULT_VIEW,
		CRect(0,0,0,0), this, nID, pContext))
	{
		TRACE(traceAppMsg, 0, "Warning: could not create view for frame.\n");
		return NULL;        // can't continue without a view
	}

	if (pView->GetExStyle() & WS_EX_CLIENTEDGE)
	{
		// remove the 3d style from the frame, since the view is
		//  providing it.
		// make sure to recalc the non-client area
		ModifyStyleEx(WS_EX_CLIENTEDGE, 0, SWP_FRAMECHANGED);
	}
	return pView;
}

BOOL CFrameWnd::OnCreateClient(LPCREATESTRUCT, CCreateContext* pContext)
{
	// default create client will create a view if asked for it
	if (pContext != NULL && pContext->m_pNewViewClass != NULL)
	{
		if (CreateView(pContext, AFX_IDW_PANE_FIRST) == NULL)
			return FALSE;
	}
	return TRUE;
}

int CFrameWnd::OnCreate(LPCREATESTRUCT lpcs)
{
	ENSURE_ARG(lpcs != NULL);
	CCreateContext* pContext = (CCreateContext*)lpcs->lpCreateParams;
	return OnCreateHelper(lpcs, pContext);
}

int CFrameWnd::OnCreateHelper(LPCREATESTRUCT lpcs, CCreateContext* pContext)
{
	if (CWnd::OnCreate(lpcs) == -1)
		return -1;

	// create special children first
	if (!OnCreateClient(lpcs, pContext))
	{
		TRACE(traceAppMsg, 0, "Failed to create client pane/view for frame.\n");
		return -1;
	}

	// post message for initial message string
	PostMessage(WM_SETMESSAGESTRING, AFX_IDS_IDLEMESSAGE);

	// make sure the child windows have been properly sized
	RecalcLayout();

	return 0;   // create ok
}

这段代码的意思是，在CSingleDocTemplate::CreateNewFrame(CDocument* pDoc, CFrameWnd* pOther)中，使得CFrameWnd::Create()得到调用，CFrameWnd::Create(...)调用CFrameWnd::CreateEx(...),此函数会使得系统在还未创建窗口前发送一个WM_CREATE消息，此消息得到CFrameWnd::OnCreate(...)响应，CFrameWnd::OnCreate(...)调用CFrameWnd::OnCreateHelper(...)函数，CFrameWnd::OnCreateHelper(...)函数会调用CFrameWnd::OnCreateClient(...)函数，而CFrameWnd::OnCreateClient(...)函数会最终调用CFrameWnd::OnCreateView(...)完成CView对象的生成。

总结过程就是：

CXXXApp::InitInstance()->CSingleTemplate::CreateNewDocument(),CSingleTemplate::CreateNewFrame()->

CFrameWnd::Create()->CFrameWnd::CreateEx()->发送WM_CREATE消息->CFrameWnd::OnCreate()->

CFrameWnd::OnCreateHelper()->CFrameWnd::OnCreateClient()->CFrameWnd::CreateView()(可算到了！)。