UpdateData()函数用法

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 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
}

 

  CDialog::OnOK()

void CDialog::OnOK()
{
 if (!UpdateData(TRUE))
 {
  TRACE(traceAppMsg, 0, "UpdateData failed during dialog termination.\n");
  // the UpdateData routine will set 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 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;
}

    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)