(转)DoDataExchange执行时机

void CRegisterDialog::DoDataExchange(CDataExchange* pDX)
{
    CDialog::DoDataExchange(pDX);

    //{{AFX_DATA_MAP(CRegisterDialog)

    DDX_Control(pDX, IDC_INCOME, m_ctrlIncome);

    DDX_LBString(pDX, IDC_INCOME, m_strIncome);

    DDX_CBString(pDX, IDC_KIND, m_strKind);
    
    DDX_Check(pDX, IDC_MARRIED, m_bMarried);

    DDX_Text(pDX, IDC_NAME, m_strName);

    DDX_Radio(pDX, IDC_SEX, m_nSex);
    
    DDX_Text(pDX, IDC_UNIT, m_strUnit);

    DDX_Radio(pDX, IDC_WORK, m_nWork);

    DDX_Text(pDX, IDC_AGE, m_nAge);

    DDV_MinMaxUInt(pDX, m_nAge, 16, 65);

    //}}AFX_DATA_MAP
}

读者可以看出，该函数中的代码是由ClassWizard自动加入的。DoDataExchange只有一个参数，即一个CDataExchange对象的指针pDX。在该函数中调用了DDX函数来完成数据交换，调用DDV函数来进行数据有效检查。

当程序需要交换数据时，不要直接调用DoDataExchange函数，而应该调用CWnd::UpdateData。UpdataData函数内部调用了DoDataExchange。该函数只有一个布尔型参数，它决定了数据传送的方向。调用UpdateData(TRUE)将数据从对话框的控件中传送到对应的数据成员中，调用UpdateData(FALSE)则将数据从数据成员中传送给对应的控件。

在缺省的CDialog::OnInitDialog中调用了UpdateData(FALSE)，这样，在对话框创建时，数据成员的初值就会反映到相应的控件上。若用户是按了OK（确定）按钮退出对话框，则对话框认为输入有效，就会调用UpdataData(TRUE)将控件中的数据传给数据成员。

下图描绘了对话框的这种数据交换机制。

VC中的DoDataExchange

怎么设置控件和变量关联呢？

假如在对话框中加入一个picture控件的话

1.导入图片

2.拉picture控件到对话框上，设置属性，Type改为Bitmap,image选择导入的图片，ID一定要修改，不能为默认的IDC_Static,否则下面将做的Classwizard将不出现此控件ID。

3.ClassWizard中选择member variable Category选择 Control加入相应的CStatic变量 。

4.此时到DoDataExchange看，增加相应的数据交换语句，我的是DDX_Control(pDX, IDC_bt, m_bt);

原文地址：http://hi.baidu.com/chinafire521/item/8f18a91a13edd8dbbf90424f

具体代码如下：

文件 dlgcore.cpp

BOOL CDialog::OnInitDialog()
{
    // execute dialog RT_DLGINIT resource
    BOOL bDlgInit;
    if (m_lpDialogInit != NULL)
        bDlgInit = ExecuteDlgInit(m_lpDialogInit);
    else
        bDlgInit = ExecuteDlgInit(m_lpszTemplateName);

    if (!bDlgInit)
    {
        TRACE(traceAppMsg, 0, "Warning: ExecuteDlgInit failed during dialog init.
");
        EndDialog(-1);
        return FALSE;
    }

    // transfer data into the dialog from member variables
    if (!UpdateData(FALSE))
    {
        TRACE(traceAppMsg, 0, "Warning: UpdateData failed during dialog init.
");
        EndDialog(-1);
        return FALSE;
    }

    // enable/disable help button automatically
    CWnd* pHelpButton = GetDlgItem(ID_HELP);
    if (pHelpButton != NULL)
        pHelpButton->ShowWindow(AfxHelpEnabled() ? SW_SHOW : SW_HIDE);

    return TRUE;    // set focus to first one
}

wincore.cpp中

BOOL CWnd::UpdateData(BOOL bSaveAndValidate)
{
    ASSERT(::IsWindow(m_hWnd)); // calling UpdateData before DoModal?

    CDataExchange dx(this, bSaveAndValidate);

    // prevent control notifications from being dispatched during UpdateData
    _AFX_THREAD_STATE* pThreadState = AfxGetThreadState();
    HWND hWndOldLockout = pThreadState->m_hLockoutNotifyWindow;
    ASSERT(hWndOldLockout != m_hWnd);   // must not recurse
    pThreadState->m_hLockoutNotifyWindow = m_hWnd;

    BOOL bOK = FALSE;       // assume failure
    TRY
    {
        DoDataExchange(&dx);
        bOK = TRUE;         // it worked
    }
    CATCH(CUserException, e)
    {
        // validation failed - user already alerted, fall through
        ASSERT(!bOK);
        // Note: DELETE_EXCEPTION_(e) not required
    }
    AND_CATCH_ALL(e)
    {
        // validation failed due to OOM or other resource failure
        e->ReportError(MB_ICONEXCLAMATION, AFX_IDP_INTERNAL_FAILURE);
        ASSERT(!bOK);
        DELETE_EXCEPTION(e);
    }
    END_CATCH_ALL

    pThreadState->m_hLockoutNotifyWindow = hWndOldLockout;
    return bOK;
}