对话框直接添加类，类向导添加时出现了问题。

因此便想通过添加C++类的方式间接实现添加对话框类。

第一步：添加C++类

#pragma once
class CWordCountDlg
{
public:
    CWordCountDlg(void);
    ~CWordCountDlg(void);
};

#include "StdAfx.h"
#include "WordCountDlg.h"
CWordCountDlg::CWordCountDlg(void)
{
}
CWordCountDlg::~CWordCountDlg(void)
{
}

第二步： 扩展成MFC对话框类

#include "resource.h"                    //0
#pragma once
class CWordCountDlg:public CDialog       //1 基类
{
        DECLARE_DYNAMIC(CWordCountDlg)        //2
public:
        // 对话框数据
        enum { IDD = IDD_WORD_COUNT };    //3对话框关联ID
public:
    CWordCountDlg(void);
    ~CWordCountDlg(void);
protected:
    virtual void DoDataExchange(CDataExchange* pDX);    //4 数据关联
    DECLARE_MESSAGE_MAP()                               //5 消息映射
public:
    virtual BOOL OnInitDialog();                        //6 初始化
    
};

#include "StdAfx.h"
#include "WordCountDlg.h"
IMPLEMENT_DYNAMIC(CWordCountDlg, CDialog)    // 0
CWordCountDlg::CWordCountDlg(void): CDialog(CWordCountDlg::IDD, NULL)  //1
{
}
CWordCountDlg::~CWordCountDlg(void)
{
}
void CWordCountDlg::DoDataExchange(CDataExchange* pDX)  //2
{
    CDialog::DoDataExchange(pDX);
}
BEGIN_MESSAGE_MAP(CWordCountDlg, CDialog)               //3
    ON_BN_CLICKED(IDOK, &CWordCountDlg::OnBnClickedOk)
END_MESSAGE_MAP()
BOOL CWordCountDlg::OnInitDialog()                     //4
{
    CDialog::OnInitDialog();
    return TRUE;  // return TRUE unless you set the focus to a control
    // 异常: OCX 属性页应返回 FALSE
}