在对话框程序中，我们经常是利用对话框上的子控件进行命令响应来处理一些事件。如果我们想要让对话框（子控件的父窗口）类来响应我们的按键消息，我们可以通过ClassWizard对WM_KEYDOWN消息进行响应，当程序运行后，我们按下键盘上的按键，但对话框不会有任何的反应。这是因为在对话框程序中，某些特定的消息，例如按键消息，它们被Windows内部的对话框过程处理了（即在基类中完成了处理，有兴趣的读者可以查看MFC的源代码），或者被发送给子控件进行处理，所以我们在对话框类中就捕获不到按键的消息了。
既然我们知道了这个处理的过程，我们就可以找到底层处理按键消息的函数，然后在子类中重载它，就可以在对话框程序中处理按键消息了。在MFC中，是利用BOOL ProcessMessageFilter(int code, LPMSG lpMsg)这个虚函数来过滤或响应菜单和对话框的特定Windows消息。下面我们通过程序给大家演示基于对话框的应用程序对WM_KEYDOWN消息的捕获。
第一步：新建一个工程，选择MFC AppWizard (exe)，工程名为WinSun，点击ok，进入下一步，选择Dialog based，点击Finish。
第二步：在CWinSunApp类上点击右键，选择Add Member Varialbe，增加一个类型为HWND，变量名m_hwndDlg的public的变量。
代码如下：
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)
{
//判断消息，如果消息是从对话框发出的或者其子控件发出的，我们就进行处理。sunxin
if((lpMsg->hwnd==m_hwndDlg) || ::IsChild(m_hwndDlg,lpMsg->hwnd))
{
//如果消息是WM_KEYDOWN，我们就弹出一个消息框。sunxin
if(lpMsg->message==WM_KEYDOWN)
{
AfxMessageBox("捕获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
//将对话框的句柄传递到CWinSunApp类中。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;
}
