WTL 学习笔记 -- DDX 和 DDV

WTL 学习笔记 -- DDX 和 DDV

 

DDX 初看时有点神秘，它把控件和相关变量关联起来了，两者在适当的时候自动进行同步。比如你在初始化时给变量赋了初值，控件上自动显示该值; 而在界面上修改了控件上的值后，它自动反应到对应的变量上去。

 

我们先看看如何使用DDX：

1.         包含相关头文件

#include

 

2.         让对话框从CWinDataExchange类继承过来

class CMainDlg : public CDialogImpl<CMainDlg>, public CUpdateUI<CMainDlg>,                    public CMessageFilter, public CIdleHandler, public CWinDataExchange<CMainDlg>

3.         建立DDX映射

BEGIN_DDX_MAP(CMainDlg)                    DDX_INT(IDC_EDIT, m_nValue)          END_DDX_MAP()

 

4.         在OnInitDialog里把变量的值更到控件

DoDataExchange();

5.         在OnOK里把控件的值更新到变量

DoDataExchange(TRUE);

 

用这么简单的代码，实现这么有用的功能，不错吧。DDX是怎么实现的呢？其实只要看一下那些宏是怎么定义，就一目了然了：

#define BEGIN_DDX_MAP(thisClass) /          BOOL DoDataExchange(BOOL bSaveAndValidate = FALSE, UINT nCtlID = (UINT)-1) /          { /                    bSaveAndValidate; /                    nCtlID;   #define DDX_INT(nID, var) /                    if(nCtlID == (UINT)-1 || nCtlID == nID) /                    { /                             if(!DDX_Int(nID, var, TRUE, bSaveAndValidate)) /                                      return FALSE; /               }          template <class Type>          BOOL DDX_Int(UINT nID, Type& nVal, BOOL bSigned, BOOL bSave, BOOL bValidate = FALSE, Type nMin = 0, Type nMax = 0)          {                    T* pT = static_cast<T*>(this);                    BOOL bSuccess = TRUE;                      if(bSave)                    {                             nVal = (Type)pT->GetDlgItemInt(nID, &bSuccess, bSigned);                    }                    else                    {                             ATLASSERT(!bValidate || nVal >= nMin && nVal <= nMax);                             bSuccess = pT->SetDlgItemInt(nID, nVal, bSigned);                    }                      if(!bSuccess)                    {                             pT->OnDataExchangeError(nID, bSave);                    }                    else if(bSave && bValidate)   // validation                    {                             ATLASSERT(nMin != nMax);                             if(nVal < nMin || nVal > nMax)                             {                                      _XData data = { ddxDataInt };                                      data.intData.nVal = (long)nVal;                                      data.intData.nMin = (long)nMin;                                      data.intData.nMax = (long)nMax;                                      pT->OnDataValidateError(nID, bSave, data);                                      bSuccess = FALSE;                             }                    }                    return bSuccess;      }

 

你看，这些宏不过是代替你调用了SetDlgItemInt和GetDlgItemInt之类的函数罢了。其它类型的数据大同小异，而控件则需要调用SubclassWindow。

 

DDV也不过是同时加上了数据检验功能吧，比如检查字符串的长度，整数的范围等。