总结《二》MFC中WinMain和CALLBACK

MFC中WinMain和回调函数CALLBACK

一，路线

       1.一般普通窗口或控件建立调用的CWnd :: CreateEx函数

       2.经过资源对话框创建的即不调用的CWnd :: CreateEx函数

二，在WIN32SDK下编程我们总是从入口函数WINMAIN和给予窗口类指定窗口回调函数（CALLBACK），如下：

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI _tWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLine, int nShowCmd )
{
	WNDCLASSEX wc = { 0 };
	wc.cbSize = sizeof(WNDCLASSEX);
	wc.hbrBackground = (HBRUSH)GetStockObject(LTGRAY_BRUSH);
	wc.hCursor = LoadCursor(nullptr, IDC_ARROW);
	wc.hIcon = LoadIcon(nullptr, IDI_APPLICATION);
	wc.hInstance = hInstance;
	wc.lpfnWndProc = WndProc;//CALLBACK

那么MFC隐藏了这些细节，我们具体来解剖下。

三，WINMAIN

      在MFC中由appmodul.cpp中声明

extern int AFXAPI AfxWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
	_In_ LPTSTR lpCmdLine, int nCmdShow);

extern "C" int WINAPI
_tWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
	_In_ LPTSTR lpCmdLine, int nCmdShow)
#pragma warning(suppress: 4985)
{
	// call shared/exported WinMain
	return AfxWinMain(hInstance, hPrevInstance, lpCmdLine, nCmdShow);
}

winmain.cpp定义

int AFXAPI AfxWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
	_In_ LPTSTR lpCmdLine, int nCmdShow)
{
	ASSERT(hPrevInstance == NULL);

	int nReturnCode = -1;
	CWinThread* pThread = AfxGetThread();
	CWinApp* pApp = AfxGetApp();

	// AFX internal initialization
	if (!AfxWinInit(hInstance, hPrevInstance, lpCmdLine, nCmdShow))
		goto InitFailure;

	// App global initializations (rare)
	if (pApp != NULL && !pApp->InitApplication())
		goto InitFailure;

	// Perform specific initializations
	if (!pThread->InitInstance())
	{
		if (pThread->m_pMainWnd != NULL)
		{
			TRACE(traceAppMsg, 0, "Warning: Destroying non-NULL m_pMainWnd\n");
			pThread->m_pMainWnd->DestroyWindow();
		}
		nReturnCode = pThread->ExitInstance();
		goto InitFailure;
	}
	nReturnCode = pThread->Run();

InitFailure:
	AfxWinTerm();
	return nReturnCode;
}

三，CALLBACK

分析上述1，先看源码，一切源码说话

BOOL CWnd::CreateEx(DWORD dwExStyle, LPCTSTR lpszClassName,
	LPCTSTR lpszWindowName, DWORD dwStyle,
	int x, int y, int nWidth, int nHeight,
	HWND hWndParent, HMENU nIDorHMenu, LPVOID lpParam)
{
	ASSERT(lpszClassName == NULL || AfxIsValidString(lpszClassName) || 
		AfxIsValidAtom(lpszClassName));
	ENSURE_ARG(lpszWindowName == NULL || AfxIsValidString(lpszWindowName));
	
	// allow modification of several common create parameters
	CREATESTRUCT cs;
	cs.dwExStyle = dwExStyle;
	cs.lpszClass = lpszClassName;
	cs.lpszName = lpszWindowName;
	cs.style = dwStyle;
	cs.x = x;
	cs.y = y;
	cs.cx = nWidth;
	cs.cy = nHeight;
	cs.hwndParent = hWndParent;
	cs.hMenu = nIDorHMenu;
	cs.hInstance = AfxGetInstanceHandle();
	cs.lpCreateParams = lpParam;

	if (!PreCreateWindow(cs))
	{
		PostNcDestroy();
		return FALSE;
	}

	AfxHookWindowCreate(this);
	HWND hWnd = CreateWindowEx(cs.dwExStyle, cs.lpszClass,
			cs.lpszName, cs.style, cs.x, cs.y, cs.cx, cs.cy,
			cs.hwndParent, cs.hMenu, cs.hInstance, cs.lpCreateParams);

	if (!AfxUnhookWindowCreate())
		PostNcDestroy();        // cleanup if CreateWindowEx fails too soon

	if (hWnd == NULL)
		return FALSE;
	ASSERT(hWnd == m_hWnd); // should have been set in send msg hook
	return TRUE;
}

在正式创建窗口前加入一个的PreCreateWindow的虚函数，这样派生类就有机会重新定义它，当我们想改变窗口类里的属性时可以从派生类覆写此虚函数，也可以我们自己注册窗口类，自己注册后直接返回TRUE即可。

BOOL CWnd::PreCreateWindow(CREATESTRUCT& cs)
{
	if (cs.lpszClass == NULL)
	{
		// make sure the default window class is registered
		VERIFY(AfxDeferRegisterClass(AFX_WND_REG));

		// no WNDCLASS provided - use child window default
		ASSERT(cs.style & WS_CHILD);
		cs.lpszClass = _afxWnd;
	}

	if ((cs.hMenu == NULL) && (cs.style & WS_CHILD))
	{
		cs.hMenu = (HMENU)(UINT_PTR)this;
	}

	return TRUE;
}

在CreateWindowEx创建窗口之前调用了AfxHookWindowCreate函数，函数源码：

void AFXAPI AfxHookWindowCreate(CWnd* pWnd)
{
	_AFX_THREAD_STATE* pThreadState = _afxThreadState.GetData();
	if (pThreadState->m_pWndInit == pWnd)
		return;

	if (pThreadState->m_hHookOldCbtFilter == NULL)
	{
		pThreadState->m_hHookOldCbtFilter = ::SetWindowsHookEx(WH_CBT,
			_AfxCbtFilterHook, NULL, ::GetCurrentThreadId());
		if (pThreadState->m_hHookOldCbtFilter == NULL)
			AfxThrowMemoryException();
	}
	ASSERT(pThreadState->m_hHookOldCbtFilter != NULL);
	ASSERT(pWnd != NULL);
	ASSERT(pWnd->m_hWnd == NULL);   // only do once

	ASSERT(pThreadState->m_pWndInit == NULL);   // hook not already in progress
	pThreadState->m_pWndInit = pWnd;
}

内部调用了SetWindowHookEx函数下了钩子，钩子类型为:WH_CBT，即在激活、创建、破坏、最小化、最大化、移动或调整窗口大小之前，系统会先调用我们下的钩子函数，即_AfxCbtFilterHook，该函数源码：

LRESULT CALLBACK
_AfxCbtFilterHook(int code, WPARAM wParam, LPARAM lParam)
{
	_AFX_THREAD_STATE* pThreadState = _afxThreadState.GetData();
	if (code != HCBT_CREATEWND)
	{
		// wait for HCBT_CREATEWND just pass others on...
		return CallNextHookEx(pThreadState->m_hHookOldCbtFilter, code,
			wParam, lParam);
	}

	LPCREATESTRUCT lpcs = ((LPCBT_CREATEWND)lParam)->lpcs;

	CWnd* pWndInit = pThreadState->m_pWndInit;
	BOOL bContextIsDLL = afxContextIsDLL;
	if (pWndInit != NULL || (!(lpcs->style & WS_CHILD) && !bContextIsDLL))
	{
		// Note: special check to avoid subclassing the IME window
		if (_afxDBCS)
		{
			// check for cheap CS_IME style first...
			if (GetClassLong((HWND)wParam, GCL_STYLE) & CS_IME)
				goto lCallNextHook;

			// get class name of the window that is being created
			LPCTSTR pszClassName;
			TCHAR szClassName[_countof("ime")+1];
			if (DWORD_PTR(lpcs->lpszClass) > 0xffff)
			{
				pszClassName = lpcs->lpszClass;
			}
			else
			{
				szClassName[0] = '\0';
#pragma warning(push)
#pragma warning(disable: 4302) // 'type cast' : truncation from 'LPCSTR' to 'ATOM'
				GlobalGetAtomName((ATOM)lpcs->lpszClass, szClassName, _countof(szClassName));
#pragma warning(pop)
				pszClassName = szClassName;
			}

			// a little more expensive to test this way, but necessary...
			if (::AfxInvariantStrICmp(pszClassName, _T("ime")) == 0)
				goto lCallNextHook;
		}

		ASSERT(wParam != NULL); // should be non-NULL HWND
		HWND hWnd = (HWND)wParam;
		WNDPROC oldWndProc;
		if (pWndInit != NULL)
		{
			AFX_MANAGE_STATE(pWndInit->m_pModuleState);

			// connect the HWND to pWndInit...
			pWndInit->Attach(hWnd);
			// allow other subclassing to occur first
			pWndInit->PreSubclassWindow();

			WNDPROC *pOldWndProc = pWndInit->GetSuperWndProcAddr();
			ASSERT(pOldWndProc != NULL);

			// subclass the window with standard AfxWndProc
			WNDPROC afxWndProc = AfxGetAfxWndProc();
			oldWndProc = (WNDPROC)SetWindowLongPtr(hWnd, GWLP_WNDPROC,
				(DWORD_PTR)afxWndProc);
			ASSERT(oldWndProc != NULL);
			if (oldWndProc != afxWndProc)
				*pOldWndProc = oldWndProc;

			pThreadState->m_pWndInit = NULL;
		}
		else
		{
			static ATOM s_atomMenu = 0;
			bool bSubclass = true;			

			if (s_atomMenu == 0)
			{
				WNDCLASSEX wc;
				memset(&wc, 0, sizeof(WNDCLASSEX));
				wc.cbSize = sizeof(WNDCLASSEX);
				s_atomMenu = (ATOM)GetClassInfoEx(NULL, _T("#32768"), &wc);
			}

			// Do not subclass menus.
			if (s_atomMenu != 0)
			{
				ATOM atomWnd = (ATOM)::GetClassLongPtr(hWnd, GCW_ATOM);
				if (atomWnd == s_atomMenu)
						bSubclass = false;
			}
			else
			{			
				TCHAR szClassName[256];
				if (::GetClassName(hWnd, szClassName, 256))
				{
					szClassName[255] = NULL;
					if (_tcscmp(szClassName, _T("#32768")) == 0)
						bSubclass = false;
				}
			}			
			if (bSubclass)
			{
				// subclass the window with the proc which does gray backgrounds
				oldWndProc = (WNDPROC)GetWindowLongPtr(hWnd, GWLP_WNDPROC);
				if (oldWndProc != NULL && GetProp(hWnd, _afxOldWndProc) == NULL)
				{
					SetProp(hWnd, _afxOldWndProc, oldWndProc);
					if ((WNDPROC)GetProp(hWnd, _afxOldWndProc) == oldWndProc)
					{
						GlobalAddAtom(_afxOldWndProc);
						SetWindowLongPtr(hWnd, GWLP_WNDPROC, (DWORD_PTR)_AfxActivationWndProc);
						ASSERT(oldWndProc != NULL);
					}
				}
			}
		}
	}

lCallNextHook:
	LRESULT lResult = CallNextHookEx(pThreadState->m_hHookOldCbtFilter, code,
		wParam, lParam);

	return lResult;
}

该函数把code不是HCBT_CREATEWND过滤，保留了HCBT_CREATEWND。

该code为一个窗口即将被创建时在向窗口发送WM_CREATE或者WM_NCCREATE消息，所以在这个时候进行了子类化操作，就是把所有的窗口回调函数设为AfxWndProc

LRESULT CALLBACK
AfxWndProc(HWND hWnd, UINT nMsg, WPARAM wParam, LPARAM lParam)
{
	// special message which identifies the window as using AfxWndProc
	if (nMsg == WM_QUERYAFXWNDPROC)
		return 1;

	// all other messages route through message map
	CWnd* pWnd = CWnd::FromHandlePermanent(hWnd);
	ASSERT(pWnd != NULL);					
	ASSERT(pWnd==NULL || pWnd->m_hWnd == hWnd);
	if (pWnd == NULL || pWnd->m_hWnd != hWnd)
		return ::DefWindowProc(hWnd, nMsg, wParam, lParam);
	return AfxCallWndProc(pWnd, hWnd, nMsg, wParam, lParam);
}