在對話框程序中，我們經常是利用對話框上的子控件進行命令響應來處理一些事件。如果我們想要讓對話框（子控件的父窗口）類來響應我們的按鍵消息，我們可以通過ClassWizard對WM_KEYDOWN消息進行響應，當程序運行后，我們按下鍵盤上的按鍵，但對話框不會有任何的反應。這是因為在對話框程序中，某些特定的消息，例如按鍵消息，它們被Windows內部的對話框過程處理了（即在基類中完成了處理，有興趣的讀者可以查看MFC的源代碼），或者被發送給子控件進行處理，所以我們在對話框類中就捕獲不到按鍵的消息了。
既然我們知道了這個處理的過程，我們就可以找到底層處理按鍵消息的函數，然后在子類中重載它，就可以在對話框程序中處理按鍵消息了。在MFC中，是利用BOOL ProcessMessageFilter(int code, LPMSG lpMsg)這個虛函數來過濾或響應菜單和對話框的特定Windows消息。下面我們通過程序給大家演示基于對話框的應用程序對WM_KEYDOWN消息的捕獲。
第一步：新建一個工程，選擇MFC AppWizard (exe)，工程名為WinSun，點擊ok，進入下一步，選擇Dialog based，點擊Finish。
第二步：在CWinSunApp類上點擊右鍵，選擇Add Member Varialbe，增加一個類型為HWND，變量名m_hwndDlg的public的變量。
代碼如下：
class CWinSunApp : public CWinApp
{
public:
HWND m_hwndDlg;
CWinSunApp();
// Overrides
// ClassWizard generated virtual function overrides
//{{AFX_VIRTUAL(CWinSunApp)
public:
virtual BOOL InitInstance();
//}}AFX_VIRTUAL
// Implementation
//{{AFX_MSG(CWinSunApp)
// NOTE - the ClassWizard will add and remove member functions here.
// DO NOT EDIT what you see in these blocks of generated code !
//}}AFX_MSG
DECLARE_MESSAGE_MAP()
};
BOOL CWinSunApp::InitInstance()
{
AfxEnableControlContainer();
// Standard initialization
// If you are not using these features and wish to reduce the size
// of your final executable, you should remove from the following
// the specific initialization routines you do not need.
#ifdef _AFXDLL
Enable3dControls(); // Call this when using MFC in a shared DLL
#else
Enable3dControlsStatic(); // Call this when linking to MFC statically
#endif
CWinSunDlg dlg;
m_pMainWnd = &dlg;
int nResponse = dlg.DoModal();
if (nResponse == IDOK)
{
// TODO: Place code here to handle when the dialog is
// dismissed with OK
}
else if (nResponse == IDCANCEL)
{
// TODO: Place code here to handle when the dialog is
// dismissed with Cancel
}
// Since the dialog has been closed, return FALSE so that we exit the
// application, rather than start the application's message pump.
m_hwndDlg=NULL;
return FALSE;
}
BOOL CWinSunApp::ProcessMessageFilter(int code, LPMSG lpMsg)
{
// TODO: Add your specialized code here and/or call the base class
if(m_hwndDlg!=NULL)
{
//判斷消息，如果消息是從對話框發出的或者其子控件發出的，我們就進行處理。sunxin
if((lpMsg->hwnd==m_hwndDlg) || ::IsChild(m_hwndDlg,lpMsg->hwnd))
{
//如果消息是WM_KEYDOWN，我們就彈出一個消息框。sunxin
if(lpMsg->message==WM_KEYDOWN)
{
AfxMessageBox("捕獲WM_KEYDOWN消息成功！");
}
}
}
return CWinApp::ProcessMessageFilter(code, lpMsg);
}
BOOL CWinSunDlg::OnInitDialog()
{
CDialog::OnInitDialog();
// Add "About..." menu item to system menu.
// IDM_ABOUTBOX must be in the system command range.
ASSERT((IDM_ABOUTBOX & 0xFFF0) == IDM_ABOUTBOX);
ASSERT(IDM_ABOUTBOX < 0xF000);
CMenu* pSysMenu = GetSystemMenu(FALSE);
if (pSysMenu != NULL)
{
CString strAboutMenu;
strAboutMenu.LoadString(IDS_ABOUTBOX);
if (!strAboutMenu.IsEmpty())
{
pSysMenu->AppendMenu(MF_SEPARATOR);
pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);
}
}
// Set the icon for this dialog. The framework does this automatically
// when the application's main window is not a dialog
SetIcon(m_hIcon, TRUE); // Set big icon
SetIcon(m_hIcon, FALSE); // Set small icon
// TODO: Add extra initialization here
//將對話框的句柄傳遞到CWinSunApp類中。sunxin
((CWinSunApp*)AfxGetApp())->m_hwndDlg=m_hWnd;
return TRUE; // return TRUE unless you set the focus to a control
}
void CWinSunDlg::OnDestroy()
{
CDialog::OnDestroy();
// TODO: Add your message handler code here
((CWinSunApp*)AfxGetApp())->m_hwndDlg=NULL;
}
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