CWnd::WindowProc的理解

先帖一段原始碼

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;}

建立一對話方塊程式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);}

此時，因為你重載了OnMouseMove，修改了訊息映射地圖，那麼在CMyButton接收MouseMove訊息的時候，會映射到

CMyButton::OnMouseMove，但是CMyButton::OnMouseMove由CButton::OnMouseMove預設處理。然後CWnd::OnWndMsg 

直接返回TRUE；那麼CWnd::WndProc下面的

lResult = DefWindowProc(message, wParam, lParam);

便不會再執行了
反之，倘若你沒重載WM_MOUSEMOVE訊息（只要注釋ON_WM_MOUSEMOVE()即可）。那麼OnWndMsg會返回FALSE，表明使用者

沒有修改訊息映射，然後

lResult = DefWindowProc(message, wParam, lParam);

會被執行，設定按鈕狀態。

但是請注意：CButton::OnMouseMove最終還是會調用CWnd::DefWindowProc這個函數，這個函數的實現如下：

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);}

看到沒，::CallWindowProc(m_pfnSuper, m_hWnd, nMsg, wParam, lParam);
這個API最終來設定按鈕在滑鼠移動上去該顯示的狀態。