爱华网UpdateData(True):表示写数据，将窗口控制变量写入内存（更新数据）-------使用OnOk时将自动调用UpdateData(True)，
用以将窗口数据写入内存相应成员变量中
UpdateData(Flase):表示读数据，即显示窗口读取内存的数据以供实时显示------使用OnInitDialog中，MFC调用UpdateData
(False)将内存成员数据显示到对应的窗口中
比如：CDialog的成员函数OnInitDialog()
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 membervariables
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);
returnTRUE; // setfocus to first one
}
CDialog::OnOK()
voidCDialog::OnOK()
{
if (!UpdateData(TRUE))
{
TRACE(traceAppMsg, 0,"UpdateData failed during dialog termination.n");
// the UpdateData routine willset focus to correct item
return;
}
EndDialog(IDOK);
}
CWnd:: UpdateData(BOOL bSaveAndValidate) //UpdateData 函数的定义
BOOL CWnd::UpdateData(BOOL bSaveAndValidate)
{
ASSERT(::IsWindow(m_hWnd)); // calling UpdateDatabefore DoModal?
CDataExchange dx(this, bSaveAndValidate);
// prevent control notifications from beingdispatched during UpdateData
_AFX_THREAD_STATE* pThreadState =AfxGetThreadState();
HWND hWndOldLockout =pThreadState->m_hLockoutNotifyWindow;
ASSERT(hWndOldLockout !=m_hWnd); // must notrecurse
pThreadState->m_hLockoutNotifyWindow= m_hWnd;
BOOL bOK =FALSE;// assume failure
TRY
{
DoDataExchange(&dx);
bOK =TRUE;// it worked
}
CATCH(CUserException, e)
{
// validation failed - useralready alerted, fall through
ASSERT(!bOK);
// Note: DELETE_EXCEPTION_(e)not required
}
AND_CATCH_ALL(e)
{
// validation failed due to OOMor 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;
}
所谓写数据，即是将外部数据写入到内存变量中（改变内存数据）
所谓读数据，显示窗口读取内存数据（不改变内存数据）
二者经常使用于如下情况：
在设置窗口数据默认值时，或将窗口数据作为控制参数传入到内存时，这时需要往内存写入数据，此时应首先调用UpdataData(TRUE)
写入之后，需要观察内存这个数据的变化，这时应该时刻读取内存数据，此时应调用UpdateData(false)
