c#一个FTP操作封装类FTPHelper

参考了网上一些代码，作了一些调整优化。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.IO;

public class FTPHelper
{
    /// <summary>
    /// FTP请求对象
    /// </summary>
    FtpWebRequest request = null;
    /// <summary>
    /// FTP响应对象
    /// </summary>
    FtpWebResponse response = null;
    /// <summary>
    /// FTP服务器地址
    /// </summary>
    public string ftpURI { get; private set; }
    /// <summary>
    /// FTP服务器IP
    /// </summary>
    public string ftpServerIP { get; private set; }
    /// <summary>
    /// FTP服务器默认目录
    /// </summary>
    public string ftpRemotePath { get; private set; }
    /// <summary>
    /// FTP服务器登录用户名
    /// </summary>
    public string ftpUserID { get; private set; }
    /// <summary>
    /// FTP服务器登录密码
    /// </summary>
    public string ftpPassword { get; private set; }

    /// <summary>  
    /// 初始化
    /// </summary>  
    /// <param name="FtpServerIP">FTP连接地址</param>  
    /// <param name="FtpRemotePath">指定FTP连接成功后的当前目录, 如果不指定即默认为根目录</param>  
    /// <param name="FtpUserID">用户名</param>  
    /// <param name="FtpPassword">密码</param>  
    public FTPHelper(string ftpServerIP, string ftpRemotePath, string ftpUserID, string ftpPassword)
    {
        this.ftpServerIP = ftpServerIP;
        this.ftpRemotePath = ftpRemotePath;
        this.ftpUserID = ftpUserID;
        this.ftpPassword = ftpPassword;
        this.ftpURI = "ftp://" + ftpServerIP + "/" + ftpRemotePath + "/";
    }
    ~FTPHelper()
    {
        if (response != null)
        {
            response.Close();
            response = null;
        }
        if (request != null)
        {
            request.Abort();
            request = null;
        }
    }
    /// <summary>
    /// 建立FTP链接,返回响应对象
    /// </summary>
    /// <param name="uri">FTP地址</param>
    /// <param name="ftpMethod">操作命令</param>
    /// <returns></returns>
    private FtpWebResponse Open(Uri uri, string ftpMethod)
    {