在MFC中，我想引入定时器技术，请你举一个Demo 代码例子 说明我改如何做

在MFC（Microsoft Foundation Class）中，定时器技术可以通过使用`SetTimer`函数来设置一个定时器，并重载`OnTimer`函数来处理定时器事件。下面是一个简单的示例代码，演示如何在MFC应用程序中使用定时器：

// MyApp.h : main header file for the application
#pragma once
#ifndef __MYAPP_H__
#define __MYAPP_H__

#include "resource.h"
#include "MyAppDlg.h"

class CMyApp : public CWinApp
{
public:
    CMyApp();
    virtual BOOL InitInstance();
};

class CMyAppDlg : public CDialogEx
{
public:
    CMyAppDlg(CWnd* pParent = nullptr);
    virtual ~CMyAppDlg();

protected:
    virtual void DoDataExchange(CDataExchange* pDX);
    virtual BOOL OnInitDialog();
    afx_msg void OnSysCommand(UINT nID, LPARAM lParam);
    afx_msg void OnPaint();
    afx_msg HCURSOR OnQueryDragIcon();
    DECLARE_MESSAGE_MAP()

private:
    int m_nTimerID; // 定时器ID
    UINT_PTR m_nElapsed; // 记录经过的时间

public:
    afx_msg void OnTimer(UINT_PTR nIDEvent); // 定时器消息处理函数
};

#endif // __MYAPP_H__

// MyApp.cpp : Defines the class behaviors for the application.
#include "stdafx.h"
#include "MyApp.h"
#include "MyAppDlg.h"
#include "afxdialogex.h"

BEGIN_MESSAGE_MAP(CMyAppDlg, CDialogEx)
    ON_WM_SYSCOMMAND()
    ON_WM_PAINT()
    ON_WM_QUERYDRAGICON()
    ON_WM_TIMER() // 添加定时器消息映射
END_MESSAGE_MAP()

CMyApp theApp;

CMyApp::CMyApp()
{
}

BOOL CMyApp::InitInstance()
{
    CWinApp::InitInstance();
    CMyAppDlg dlg;
    m_pMainWnd = &dlg;
    dlg.DoModal();
    return FALSE;
}

CMyAppDlg::CMyAppDlg(CWnd* pParent /*=nullptr*/)
    : CDialogEx(IDD_MYAPP_DIALOG, pParent), m_nTimerID(1), m_nElapsed(0)
{
}

CMyAppDlg::~CMyAppDlg()
{
    KillTimer(m_nTimerID); // 销毁定时器
}

void CMyAppDlg::DoDataExchange(CDataExchange* pDX)
{
    CDialogEx::DoDataExchange(pDX);
}

BOOL CMyAppDlg::OnInitDialog()
{
    CDialogEx::OnInitDialog();
    SetTimer(m_nTimerID, 1000, NULL); // 设置定时器，每秒触发一次
    return TRUE;
}

void CMyAppDlg::OnSysCommand(UINT nID, LPARAM lParam)
{
    if ((nID & 0xFFF0) == IDM_ABOUTBOX)
    {
        CAboutDlg aboutDlg;
        aboutDlg.DoModal();
    }
    else
    {
        CDialogEx::OnSysCommand(nID, lParam);
    }
}

void CMyAppDlg::OnPaint()
{
    if (IsIconic())
    {
        CPaintDC dc(this); // device context for painting
        SendMessage(WM_ICONERASEBKGND, reinterpret_cast<WPARAM>(dc.GetSafeHdc()), 0);
        int cxIcon = GetSystemMetrics(SM_CXICON);
        int cyIcon = GetSystemMetrics(SM_CYICON);
        CRect rect;
        GetClientRect(&rect