(轉)DoDataExchange執行時機

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
}

讀者能夠看出，該函數中的代碼是由ClassWizard自動加入的。DoDataExchange只有一個參數，即一個CDataExchange對象的指針pDX。在該函數中調用了DDX函數來完成數據交換，調用DDV函數來進行數據有效檢查。

當程序須要交換數據時，不要直接調用DoDataExchange函數，而應該調用CWnd::UpdateData。UpdataData函數內部調用了DoDataExchange。該函數只有一個布爾型參數，它決定了數據傳送的方向。調用UpdateData(TRUE)將數據從對話框的控件中傳送到對應的數據成員中，調用UpdateData(FALSE)則將數據從數據成員中傳送給對應的控件。

在缺省的CDialog::OnInitDialog中調用了UpdateData(FALSE)，這樣，在對話框建立時，數據成員的初值就會反映到相應的控件上。若用戶是按了OK（肯定）按鈕退出對話框，則對話框認爲輸入有效，就會調用UpdataData(TRUE)將控件中的數據傳給數據成員。

下圖描繪了對話框的這種數據交換機制。

VC中的DoDataExchange

怎麼設置控件和變量關聯呢？

假如在對話框中加入一個picture控件的話

1.導入圖片

2.拉picture控件到對話框上，設置屬性，Type改成Bitmap,image選擇導入的圖片，ID必定要修改，不能爲默認的IDC_Static,不然下面將作的Classwizard將不出現此控件ID。

3.ClassWizard中選擇member variable Category選擇 Control加入相應的CStatic變量 。

4.此時到DoDataExchange看，增長相應的數據交換語句，個人是DDX_Control(pDX, IDC_bt, m_bt);

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

 

具體代碼以下：

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.\n");
        EndDialog(-1);
        return FALSE;
    }

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