CWnd::WindowProc的理解

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先帖一段源代码

LRESULT CWnd::WindowProc(UINT message, WPARAM wParam, LPARAM lParam){// OnWndMsg does most of the work, except for DefWindowProc callLRESULT lResult = 0;if (!OnWndMsg(message, wParam, lParam, &lResult))lResult = DefWindowProc(message, wParam, lParam);return lResult;}

新建一对话框程序CTestDlg，在其中添加 class CMyButton : public CButton{};

#include "stdafx.h"#include "TestCom.h"#include "MyButton.h"// CMyButtonIMPLEMENT_DYNAMIC(CMyButton, CButton)CMyButton::CMyButton(){}CMyButton::~CMyButton(){}BEGIN_MESSAGE_MAP(CMyButton, CButton)ON_WM_MOUSEMOVE()END_MESSAGE_MAP()// CMyButton message handlersvoid CMyButton::OnMouseMove(UINT nFlags, CPoint point){// TODO: Add your message handler code here and/or call defaultTRACE(L"CMyButton::OnMouseMove\n");CButton::OnMouseMove(nFlags, point);}BOOL CMyButton::OnWndMsg(UINT message, WPARAM wParam, LPARAM lParam, LRESULT* pResult){// TODO: Add your specialized code here and/or call the base classif (message == WM_MOUSEMOVE) {int a = 20;}return CButton::OnWndMsg(message, wParam, lParam, pResult);}

此时，因为你重载了OnMouseMove，修改了消息映射地图，那么在CMyButton接收MouseMove消息的时候，会映射到

CMyButton::OnMouseMove，但是CMyButton::OnMouseMove由CButton::OnMouseMove默认处理。然后CWnd::OnWndMsg

直接返回TRUE；那么CWnd::WndProc下面的

lResult = DefWindowProc(message, wParam, lParam);

便不会再执行了
反之，倘若你没重载WM_MOUSEMOVE消息（只要注释ON_WM_MOUSEMOVE()即可）。那么OnWndMsg会返回FALSE，表明用户

没有修改消息映射，然后

lResult = DefWindowProc(message, wParam, lParam);

会被执行，设定按钮状态。

但是请注意：CButton::OnMouseMove最终还是会调用CWnd::DefWindowProc这个函数，这个函数的实现如下：

LRESULT CWnd::DefWindowProc(UINT nMsg, WPARAM wParam, LPARAM lParam){if (m_pfnSuper != NULL)return ::CallWindowProc(m_pfnSuper, m_hWnd, nMsg, wParam, lParam);WNDPROC pfnWndProc;if ((pfnWndProc = *GetSuperWndProcAddr()) == NULL)return ::DefWindowProc(m_hWnd, nMsg, wParam, lParam);elsereturn ::CallWindowProc(pfnWndProc, m_hWnd, nMsg, wParam, lParam);}

看到没，::CallWindowProc(m_pfnSuper, m_hWnd, nMsg, wParam, lParam);
这个API最终来设定按钮在鼠标移动上去该显示的状态。