FTP作为日常工作学习中，非常重要的一个文件传输存储空间，想必大家都非常的熟悉了，那么如何快速的实现文件的上传下载功能呢，本文以一个简单的小例子，简述如何通过FluentFTP实现文件的上传和下载功能。仅供学习分享使用，如有不足之处，还请指正。

FTP基础知识

文件传输协议（File Transfer Protocol，FTP）是用于在网络上进行文件传输的一套标准协议，它工作在 OSI 模型的第七层， TCP 模型的第四层， 即应用层， 使用 TCP 传输而不是 UDP， 客户在和服务器建立连接前要经过一个“三次握手”的过程， 保证客户与服务器之间的连接是可靠的， 而且是面向连接， 为数据传输提供可靠保证。FTP允许用户以文件操作的方式（如文件的增、删、改、查、传送等）与另一主机相互通信。然而， 用户并不真正登录到自己想要存取的计算机上面而成为完全用户， 可用FTP程序访问远程资源， 实现用户往返传输文件、目录管理以及访问电子邮件等等， 即使双方计算机可能配有不同的操作系统和文件存储方式。

FTP环境搭建

在windows操作系统中，FTP可以通过(Internet Inforamtion Services， IIS)管理器进行创建，创建成功后即可进行查看，如下所示：

FluentFTP安装

FluentFTP是一款基于.Net的FTP和FTPS的客户端动态库，操作简单便捷。

首先创建基于.Net Framework 4.6.1的winform应用程序，然后通过Nuget包管理器进行安装，如下所示：

示例演示

 主要实现基于FTP的上传，下载，浏览等功能，如下所示：

 进入文件夹及右键下载，如下所示：

示例源码

FtpHelper类源码，封装了FTP文件的检索，上传，下载等功能，如下所示：

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using FluentFTP;

namespace DemoFtp
{
    public class FtpHelper
    {
        #region 属性与构造函数

        /// <summary>
        /// IP地址
        /// </summary>
        public string IpAddr { get; set; }

        /// <summary>
        /// 相对路径
        /// </summary>
        public string RelatePath { get; set; }

        /// <summary>
        /// 端口号
        /// </summary>
        public int Port { get; set; }

        /// <summary>
        /// 用户名
        /// </summary>
        public string UserName { get; set; }

        /// <summary>
        /// 密码
        /// </summary>
        public string Password { get; set; }

        public FtpHelper()
        {

        }

        public FtpHelper(string ipAddr, int port, string userName, string password, string relatePath)
        {
            this.IpAddr = ipAddr;
            this.Port = port;
            this.UserName = userName;
            this.Password = password;
            this.RelatePath = relatePath;
        }

        #endregion

        #region 方法

        public FtpListItem[] ListDir() {
            FtpListItem[] lists;
            using (var ftpClient = new FtpClient(this.IpAddr, this.UserName, this.Password, this.Port))
            {
                ftpClient.Connect();
                ftpClient.SetWorkingDirectory(this.RelatePath);
                lists = ftpClient.GetListing();
            }
            return lists;
        }

        public void UpLoad(string dir, string file, out bool isOk)
        {
            isOk = false;
            FileInfo fi = new FileInfo(file);
            using (FileStream fs = fi.OpenRead())
            {
                //long length = fs.Length;
                using (var ftpClient = new FtpClient(this.IpAddr, this.UserName, this.Password, this.Port))
                {
                    ftpClient.Connect();
                    ftpClient.SetWorkingDirectory(this.RelatePath);
                    string remotePath = dir + "/" + Path.GetFileName(file);
                    var ftpRemodeExistsMode = file.EndsWith(".txt") ? FtpRemoteExists.Overwrite : FtpRemoteExists.Skip;
                    FtpStatus status = ftpClient.UploadStream(fs, remotePath, ftpRemodeExistsMode, true);
                    isOk = status == FtpStatus.Success;

                }
            }

        }

        /// <summary>
        /// 上传多个文件
        /// </summary>
        /// <param name="files"></param>
        /// <param name="isOk"></param>
        public void UpLoad(string dir, string[] files, out bool isOk)
        {
            isOk = false;
            if (CheckDirIsExists(dir))
            {
                foreach (var file in files)
                {
                    UpLoad(dir, file, out isOk);
                }
            }
        }


        private bool CheckDirIsExists(string dir)
        {
            bool flag = false;
            using (var ftpClient = new FtpClient(this.IpAddr, this.UserName, this.Password, this.Port))
            {
                ftpClient.Connect();
                ftpClient.SetWorkingDirectory(this.RelatePath);
                flag = ftpClient.DirectoryExists(dir);
                if (!flag)
                {
                    flag = ftpClient.CreateDirectory(dir);
                }
            }
            return flag;


        }

        /// <summary>
        /// 下载ftp
        /// </summary>
        /// <param name="localAddress"></param>
        /// <param name="remoteAddress"></param>
        /// <returns></returns>
        public bool DownloadFile(string localAddress, string remoteAddress)
        {
            using (var ftpClient = new FtpClient(this.IpAddr, this.UserName, this.Password, this.Port))
            {
                ftpClient.SetWorkingDirectory("/");
                ftpClient.Connect();
                if (ftpClient.DownloadFile(localAddress, remoteAddress) == FtpStatus.Success)
                {
                    return true;
                }
                return false;
            }
        }

        #endregion
    }
}

每一个FTP文件或文件夹，由一个自定义用户控件【PictureBox+Label+ContextMenu】表示，这样便于处理与显示：

using DemoFtp.Properties;
using FluentFTP;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace DemoFtp
{
    public partial class FtpElementControl : UserControl
    {
        public Action<FtpListItem> SubFolderClick;

        public Action<FtpListItem> DownLoadClick;

        private FtpListItem ftpListItem;

        public FtpElementControl(FtpListItem ftpListItem)
        {
            InitializeComponent();
            this.ftpListItem = ftpListItem;
        }

        public FtpElementControl()
        {
            InitializeComponent();
        }

        public void InitControl()
        {
            if (ftpListItem.Type == FtpObjectType.Directory)
            {
                this.pbIcon.Image = Resources.folder.ToBitmap();
            }
            else if (ftpListItem.Type == FtpObjectType.File)
            {
                var name = ftpListItem.Name;
                var ext = Path.GetExtension(name).ToLower().Substring(1);
                if (ext == "png" || ext == "jpeg" || ext == "jpg" || ext == "bmp" || ext == "gif")
                {
                    this.pbIcon.Image = Resources.pictures.ToBitmap();
                }
                else if (ext == "doc" || ext == "docx")
                {
                    this.pbIcon.Image = Resources.doc.ToBitmap();
                }
                else if (ext == "exe")
                {
                    this.pbIcon.Image = Resources.setup.ToBitmap();
                }
                else
                {
                    this.pbIcon.Image = Resources.file;
                }
            }
            else
            {
                this.pbIcon.Image = Resources.file;
            }
            this.lblName.Text = ftpListItem.Name;
        }

        private void FtpElementControl_Load(object sender, EventArgs e)
        {

        }

        /// <summary>
        /// 子菜单下载功能
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void menu_ItemClicked(object sender, ToolStripItemClickedEventArgs e)
        {
            this.DownLoadClick?.Invoke(ftpListItem);
        }

        /// <summary>
        /// 双击打开
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void pbIcon_DoubleClick(object sender, EventArgs e)
        {
            this.SubFolderClick?.Invoke(ftpListItem);
        }
    }
}

主页面由一系列用户操作框和按钮组成，完成对FTP的基本操作，如下所示：

using FluentFTP;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace DemoFtp
{
    public partial class MainForm : Form
    {
        private FtpHelper ftpHelper;

        public MainForm()
        {
            InitializeComponent();
        }

        private void btnLogin_Click(object sender, EventArgs e)
        {
            var url = txtFtpUrl.Text;
            var userName = txtUserName.Text;
            var password = txtPassword.Text;
            var port = txtPort.Text;
            if (this.lblRelatePath.Text != "/")
            {
                this.lblRelatePath.Text = "/";
            }
            var relatePath = this.lblRelatePath.Text;
            if (string.IsNullOrEmpty(url) || string.IsNullOrEmpty(userName) || string.IsNullOrEmpty(password) || string.IsNullOrEmpty(port))
            {
                MessageBox.Show("路径和账号密码不可为空");
                return;
            }
            if (ftpHelper == null)
            {
                ftpHelper = new FtpHelper(url, int.Parse(port), userName, password, relatePath);

            }
            ListDir();
        }

        public void SubFolder(FtpListItem ftpListItem)
        {
            if (ftpListItem.Type == FtpObjectType.Directory)
            {
                var fullName = ftpListItem.FullName;
                ftpHelper.RelatePath = fullName;
                ListDir();
                this.lblRelatePath.Text = fullName;
            }
        }


        private void Download(FtpListItem ftpListItem) {
            var fullName=ftpListItem.FullName;
            var fileName = Path.GetFileName(fullName);
            SaveFileDialog sfd = new SaveFileDialog();
            sfd.FileName = fileName;
            sfd.Title = "不载";
            sfd.Filter = "所有文档|*.*";
            if (DialogResult.OK == sfd.ShowDialog()) {
                ftpHelper.DownloadFile(sfd.FileName, fullName);
            }
        }

        private void ListDir()
        {
            this.ftpContainer.Controls.Clear();
            var ftpListItems = this.ftpHelper.ListDir();
            if (ftpListItems != null && ftpListItems.Length > 0)
            {
                foreach (var ftpListItem in ftpListItems)
                {
                    FtpElementControl ftpControl = new FtpElementControl(ftpListItem);
                    ftpControl.InitControl();
                    ftpControl.DownLoadClick += Download;
                    ftpControl.SubFolderClick += SubFolder;
                    this.ftpContainer.Controls.Add(ftpControl);
                }
            }
        }

        private void btnUpload_Click(object sender, EventArgs e)
        {
            OpenFileDialog ofd = new OpenFileDialog();
            ofd.Filter = "所有文件|*.*";
            ofd.Title = "请选择需要上传的文件";
            if (DialogResult.OK == ofd.ShowDialog()) {
                var localFile=ofd.FileName;
                ftpHelper.UpLoad(this.lblRelatePath.Text, localFile, out bool isOk);
                if (isOk) {
                    ListDir();
                }
            }
        }

        private void pbReturn_Click(object sender, EventArgs e)
        {
            var relativePath=this.lblRelatePath.Text;
            if (relativePath == "/") {
                return;
            }
            relativePath = relativePath.Substring(0, relativePath.LastIndexOf("/")+1);
            ftpHelper.RelatePath=relativePath;
            ListDir();
            this.lblRelatePath.Text = relativePath;
        }
    }
}

以上就是基于FluentFTP实现FTP上传下载的全部内容，旨在抛砖引玉，共同学习，一起进步。