能运用 CAsyncSocket 类开发一个简单的网络聊天程序

当然可以！以下是一个使用 `CAsyncSocket` 类开发的简单的网络聊天程序示例：

// ChatClientDlg.h
#pragma once
#include "afxsock.h"

class CChatClientDlg : public CDialogEx
{
public:
    CChatClientDlg(CWnd* pParent = NULL);

    enum { IDD = IDD_CHATCLIENT_DIALOG };

protected:
    virtual void DoDataExchange(CDataExchange* pDX);

protected:
    HICON m_hIcon;
    CAsyncSocket m_socket;
    CString m_strServerIP;
    UINT m_nServerPort;
    CString m_strName;

    void AppendMessage(LPCTSTR lpszMessage);
    void OnReceive();

    DECLARE_MESSAGE_MAP()
public:
    virtual BOOL OnInitDialog();
    afx_msg void OnPaint();
    afx_msg HCURSOR OnQueryDragIcon();
    afx_msg void OnBnClickedButtonConnect();
    afx_msg void OnBnClickedButtonSend();
    afx_msg void OnClose();
};

// ChatClientDlg.cpp
#include "stdafx.h"
#include "ChatClient.h"
#include "ChatClientDlg.h"
#include "afxdialogex.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#endif

CChatClientDlg::CChatClientDlg(CWnd* pParent /*=NULL*/)
    : CDialogEx(IDD_CHATCLIENT_DIALOG, pParent)
    , m_strServerIP(_T("127.0.0.1"))
    , m_nServerPort(12345)
    , m_strName(_T(""))
{
    m_hIcon = AfxGetApp()->LoadIcon(IDR_MAINFRAME);
}

void CChatClientDlg::DoDataExchange(CDataExchange* pDX)
{
    CDialogEx::DoDataExchange(pDX);
    DDX_Text(pDX, IDC_EDIT_SERVER_IP, m_strServerIP);
    DDX_Text(pDX, IDC_EDIT_SERVER_PORT, m_nServerPort);
    DDX_Text(pDX, IDC_EDIT_NAME, m_strName);
}

BEGIN_MESSAGE_MAP(CChatClientDlg, CDialogEx)
    ON_WM_PAINT()
    ON_WM_QUERYDRAGICON()
    ON_BN_CLICKED(IDC_BUTTON_CONNECT, &CChatClientDlg::OnBnClickedButtonConnect)
    ON_BN_CLICKED(IDC_BUTTON_SEND, &CChatClientDlg::OnBnClickedButtonSend)
    ON_WM_CLOSE()
END_MESSAGE_MAP()

BOOL CChatClientDlg::OnInitDialog()
{
    CDialogEx::OnInitDialog();

    SetIcon(m_hIcon, TRUE);
    SetIcon(m_hIcon, FALSE);

    return TRUE;
}

void CChatClientDlg::OnPaint()
{
    if (IsIconic())
    {
        CPaintDC dc(this); // device context for painting

        SendMessage(WM_ICONERASEBKGND, reinterpret_cast<WPARAM>(dc.GetSafeHdc()), 0);

        // Center icon in client rectangle
        int cxIcon = GetSystemMetrics(SM_CXICON);
        int cyIcon = GetSystemMetrics(SM_CYICON);
        CRect rect;
        GetClientRect(&rect);
        int x = (rect.Width() - cxIcon + 1) / 2;
        int y = (rect.Height() - cyIcon + 1) / 2;

        // Draw the icon
        dc.DrawIcon(x, y, m_hIcon);
    }
    else
    {
        CDialogEx::OnPaint();
    }
}

HCURSOR CChatClientDlg::OnQueryDragIcon()
{
    return static_cast<HCURSOR>(m_hIcon);
}

void CChatClientDlg::OnBnClickedButtonConnect()
{
    if (!m_socket.Create())
    {
        AfxMessageBox(_T("Failed to create socket!"));
        return;
    }

    if (!m_socket.Connect(m_strServerIP, m_nServerPort))
    {
        AfxMessageBox(_T("Failed to connect to server!"));
        return;
    }

    CString strMessage;
    strMessage.Format(_T("%s joined the chat."), m_strName);
    m_socket.Send(strMessage, strMessage.GetLength() * sizeof(TCHAR));

    GetDlgItem(IDC_BUTTON_CONNECT)->EnableWindow(FALSE);
    GetDlgItem(IDC_EDIT_SERVER_IP)->EnableWindow(FALSE);
    GetDlgItem(IDC_EDIT_SERVER_PORT)->EnableWindow(FALSE);
    GetDlgItem(IDC_EDIT_NAME)->EnableWindow(FALSE);

    OnReceive();
}

void CChatClientDlg::OnBnClickedButtonSend()
{
    CString strMessage;
    GetDlgItemText(IDC_EDIT_MESSAGE, strMessage);

    if (!strMessage.IsEmpty())
    {
        CString strFinalMessage;
        strFinalMessage.Format(_T("%s: %s"), m_strName, strMessage);
        m_socket.Send(strFinalMessage, strFinalMessage.GetLength() * sizeof(TCHAR));
        SetDlgItemText(IDC_EDIT_MESSAGE, _T(""));
        AppendMessage(strFinalMessage);
    }
}

void CChatClientDlg::OnClose()
{
    CString strMessage;
    strMessage.Format(_T("%s left the chat."), m_strName);
    m_socket.Send(strMessage, strMessage.GetLength() * sizeof(TCHAR));
    m_socket.ShutDown();
    CDialogEx::OnClose();
}

void CChatClientDlg::AppendMessage(LPCTSTR lpszMessage)
{
    CString strMessage;
    GetDlgItemText(IDC_EDIT_MESSAGES, strMessage);
    strMessage += _T("\r\n");
    strMessage += lpszMessage;
    SetDlgItemText(IDC_EDIT_MESSAGES, strMessage);
}

void CChatClientDlg::OnReceive()
{
    char szBuffer[1024];
    int nReceived = m_socket.Receive(szBuffer, sizeof(szBuffer));
    if (nReceived > 0)
    {
        szBuffer[nReceived] = 0;
        AppendMessage(CString(szBuffer));
    }
    OnReceive(); // 继续等待下一条消息
}

这是一个简单的客户端，它通过 `CAsyncSocket` 类与服务器进行连接，并在连接成功后发送聊天消息。在收到聊天消息时，它将消息显示在 UI 上。

这个程序的 UI 包括一个编辑框（用于输入聊天消息）、一个发送按钮、一个服务器 IP 地址编辑框、一个服务器端口号编辑框、一个用户名编辑框、一个连接按钮和一个消息列表框。当用户输入用户名并按下连接按钮时，程序将尝试连接到服务器，并发送一个包含用户名的消息。当用户输入聊天消息并按下发送按钮时，程序将将消息发送到服务器。收到的聊天消息将显示在消息列表框中。

当用户关闭程序时，程序将发送一个包含用户名的消息，然后关闭网络连接。

请注意，这只是一个简单的示例，它并没有处理错误、异常情况或其他复杂情况。在实际的应用程序中，你需要更加谨慎地处理这些情况。