?using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
//添加的命名空間引用
using System.Net;
using System.Net.Sockets;
using System.IO;
namespace ReceiveMailExample
{
    public partial class FormReceiveMail : Form
    {
        private string pop3Server;
        private TcpClient tcpClient;
        private NetworkStream networkStream;
        private StreamReader sr;
        private StreamWriter sw;
        public FormReceiveMail()
        {
            InitializeComponent();
        }
        //單擊建立連接按鈕觸發的事件
        private void buttonConnect_Click(object sender, EventArgs e)
        {
            //設置鼠標光標為等待狀態
            Cursor.Current = Cursors.WaitCursor;
            try
            {
                int index = textBoxUser.Text.IndexOf('@');
                //大部分pop3服務器都加前綴pop3.，這里僅獲取這種服務器
                //對不以pop3.為前綴的這個例子未進行處理
                pop3Server = "pop3." + textBoxUser.Text.Substring(index + 1);
                //建立與POP3服務器的連接，使用默認端口110
                tcpClient = new TcpClient(pop3Server, 110);
                listBoxStatus.Items.Add("與pop3服務器連接成功");
            }
            catch
            {
                MessageBox.Show("與服務器連接失敗");
                return;
            }
            string str;
            listBoxStatus.Items.Clear();
            //獲取 Networkstream對象，以便通過建立好的連接發送和接收數據
            networkStream = tcpClient.GetStream();
            //得到讀對象，并查找字節順序標記，防止顯示亂碼
            sr = new StreamReader(networkStream);
            //得到寫對象
            sw = new StreamWriter(networkStream);
            //讀取服務器回送的連接信息
            if (ReadDataFromServer() == null) return;
            //向服務器發送用戶名，請求確認
            if (SendDataToServer("USER " + textBoxUser.Text) == false) return;
            if (ReadDataFromServer() == null) return;
            //向服務器發送密碼，請求確認
            if (SendDataToServer("PASS " + textBoxPassword.Text) == false) return;
            if (ReadDataFromServer() == null) return;
            //向服務器發送STAT命令，請求獲取郵件總數和總字節數
            if (SendDataToServer("LIST") == false) return;
            if ((str = ReadDataFromServer()) == null) return;
            string[] splitString = str.Split(' ');
            //從字符串中取子串獲取郵件總數
            int count = int.Parse(splitString[1]);
            //判斷郵箱中是否有郵件
            if (count > 0)
            {
                //設置對應狀態信息
                buttonRead.Enabled = true;
                buttonDelete.Enabled = true;
                listBoxOperation.Items.Clear();
                groupBoxOperation.Text = "信箱中共有 " + splitString[1] + " 封郵件";
                //向郵件列表框中添加郵件
                for (int i = 0; i < count; i++)
                {
                    if ((str = ReadDataFromServer()) == null) return;
                    splitString = str.Split(' ');
                    listBoxOperation.Items.Add(string.Format(
                        "第{0}封郵件，{1}字節", splitString[0], splitString[1]));
                }
                listBoxOperation.SelectedIndex = 0;
                //讀出結束符
                if ((str = ReadDataFromServer()) == null) return;
            }
            else
            {
                groupBoxOperation.Text = "信箱中沒有郵件";
                buttonRead.Enabled = false;
                buttonDelete.Enabled = false;
            }
            buttonConnect.Enabled = false;
            buttonDisconnect.Enabled = true;
            //設置鼠標光標為默認光標
            Cursor.Current = Cursors.Default;
        }
        //向服務器發送信息
        private bool SendDataToServer(string str)
        {
            try
            {
                sw.WriteLine(str);
                sw.Flush();
                listBoxStatus.Items.Add("發送：" + str);
                return true;
            }
            catch (Exception err)
            {
                MessageBox.Show(err.Message, "發送 " + str + " 失敗");
                return false;
            }
        }
        //從網絡流中讀取服務器回送的信息
        private string ReadDataFromServer()
        {
            //從流中讀取服務器返回的信息，寫入信息列表框
            string str = null;
            try
            {
                str = sr.ReadLine();
                listBoxStatus.Items.Add("收到：" + str);
                //如果是-ERR，表明有錯
                if (str[0] == '-')
                {
                    MessageBox.Show(str, "有錯了");
                    str = null;
                }
            }
            catch (Exception err)
            {
                MessageBox.Show(err.Message, "無法讀取");
            }
            return str;
        }
        //單擊斷開連接按鈕觸發的事件
        private void buttonDisconnect_Click(object sender, EventArgs e)
        {
            //向服務器發送QUIT命令
            SendDataToServer("QUIT");
            sr.Close();
            sw.Close();
            networkStream.Close();
            tcpClient.Close();
            listBoxOperation.Items.Clear();
            richTextBox1.Clear();
            listBoxStatus.Items.Clear();
            buttonConnect.Enabled = true;
            buttonDisconnect.Enabled = false;
        }
        //單擊閱讀信件按鈕觸發的事件
        private void buttonRead_Click(object sender, EventArgs e)
        {
            //設置鼠標光標為等待狀態
            Cursor.Current = Cursors.WaitCursor;
            string mailMessage = listBoxOperation.SelectedItem.ToString();
            mailMessage = mailMessage.Substring(1, mailMessage.IndexOf("封") - 1);
            if (SendDataToServer("RETR " + mailMessage) == false) return;
            string receiveData = sr.ReadToEnd();
            //例子未進行解碼處理
            //而僅僅將源代碼原樣顯示出來，所以看到的涉及具體內容的信息將會是亂碼
            richTextBox1.Text = "源代碼：\r\n";
            richTextBox1.AppendText(receiveData);
            //設置鼠標光標為默認光標
            Cursor.Current = Cursors.Default;
        }
        //單擊刪除信件按鈕觸發的事件
        private void buttonDelete_Click(object sender, EventArgs e)
        {
            string str = listBoxOperation.SelectedItem.ToString();
            str = str.Substring(1, str.IndexOf("封") - 1);
            if (SendDataToServer("DELE " + str) == true)
            {
                richTextBox1.Clear();
                int j = listBoxOperation.SelectedIndex;
                listBoxOperation.Items.Remove(listBoxOperation.Items[j].ToString());
                MessageBox.Show("刪除成功", "恭喜");
            }
        }

        private void FormReceiveMail_Load(object sender, EventArgs e)
        {

        }
    }
}