UDP写的点对点的聊天程序，需要写IP

如果下面的代码有错误或者有不懂的地方可以联系QQ：41305987

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Net.Sockets;
using System.Net;
using System.Threading;

namespace point_talk_to_face
{
    public partial class Form1 : Form
    {
      
        public Form1()
        {
            InitializeComponent();
        }
        private Thread th;
        UdpClient udp, udp2;
        bool l = true;
        private void textBox2_TextChanged(object sender, EventArgs e)
        {

        }

        private void Form1_Load(object sender, EventArgs e)
        {
           System.Windows.Forms.Control.CheckForIllegalCrossThreadCalls = false; 
           th = new Thread(new ThreadStart(Listen));
           th.Start();
        }

        private void button1_Click(object sender, EventArgs e)
        {
   /*****************************SEND****************************************************/
                udp2 = new UdpClient(textBox3.Text,9999);
                Byte[] data = Encoding.ASCII.GetBytes(textBox2.Text);
                udp2.Send(data, data.Length);
                textBox1.AppendText("我对"+textBox3.Text+"说："+textBox2.Text+"\n");
                udp2.Close();
               this.textBox2.Clear();
                textBox2.Focus();
   /**********************************SEND*****************************************************/
        }
        private void Listen()
        {
  /********************************************RECEIVE**************************************************/
            udp = new UdpClient(9999);
            IPEndPoint remoteiep = new IPEndPoint(IPAddress.Any, 9999);

            while (l)
            {
                try
                {
                    Byte[] data = udp.Receive(ref remoteiep);

                    if (data.Length > 0)
                    {
                        string word = Encoding.ASCII.GetString(data);
                        label1.Text = remoteiep.Address.ToString();
                        label2.Text = remoteiep.Port.ToString();
                        textBox1.AppendText(label1.Text + "对我说：" + word.ToString() + "\n");
                    }
                    else
                    {
                        
                    }
                }
                catch (Exception ex)
                {
            //        textBox1.AppendText(ex.Message);
            //          MessageBox.Show(ex.Message.ToString());
                }
            }
    /*******************************************RECEIVE***********************************************************/
        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {
        }

        private void close(object sender, FormClosingEventArgs e)
        {  
            th.Abort();
            l = false;
            udp.Close();
        }

        private void Form1_FormClosed(object sender, FormClosedEventArgs e)
        {
        }
    }
}