using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
//添加的命名空间引用
using System.Net;
using System.Net.Sockets;
using System.Threading;
namespace MulticastExample
{
    public partial class FormMulticast : Form
    {
        delegate void AppendStringCallback(string text);
        AppendStringCallback appendStringCallback;
        //使用的接收端口号
        private int port = 8001;
        private UdpClient udpClient;
        public FormMulticast()
        {
            InitializeComponent();
            appendStringCallback = new AppendStringCallback(AppendString);
        }
        private void AppendString(string text)
        {
            if (richTextBox1.InvokeRequired == true)
            {
                this.Invoke(appendStringCallback, text);
            }
            else
            {
                richTextBox1.AppendText(text + "\r\n");
            }
        }
        private void ReceiveData()
        {
            //在本机指定的端口接收
            udpClient = new UdpClient(port);
            //必须使用组播地址范围内的地址
            udpClient.JoinMulticastGroup(IPAddress.Parse("237.255.255.255"));
            udpClient.Ttl = 50;
            IPEndPoint remote = new IPEndPoint(IPAddress.Parse("237.255.255.255"),port);
            //接收从远程主机发送过来的信息；
            while (true)
            {
                try
                {
                    //关闭udpClient时此句会产生异常
                    byte[] bytes = udpClient.Receive(ref remote);
                    string str = Encoding.UTF8.GetString(bytes, 0, bytes.Length);
                    AppendString(string.Format("来自{0}：{1}", remote, str));
                }
                catch
                {
                    //退出循环，结束线程
                    break;
                }
            }
        }
        private void Send(string str)
        {
            UdpClient myUdpClient = new UdpClient();
            //允许发送和接收广播数据报
            myUdpClient.EnableBroadcast = true;
            //必须使用组播地址范围内的地址
            IPEndPoint iep = new IPEndPoint(IPAddress.Parse("237.255.255.255"), 8001);
            //将发送内容转换为字节数组
            byte[] bytes = System.Text.Encoding.UTF8.GetBytes(str);
            try
            {
                //向子网发送信息
                myUdpClient.Send(bytes, bytes.Length, iep);
                textBox1.Clear();
                textBox1.Focus();
            }
            catch (Exception err)
            {
                MessageBox.Show(err.Message, "发送失败");
            }
            finally
            {
                myUdpClient.Close();
            }
        }
        private void buttonSend_Click(object sender, EventArgs e)
        {
            Send(textBox1.Text);
        }

        private void FormMulticast_Load(object sender, EventArgs e)
        {
            Thread myThread = new Thread(new ThreadStart(ReceiveData));
            myThread.Start();
        }

        private void FormMulticast_FormClosing(object sender, FormClosingEventArgs e)
        {
            udpClient.Close();
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            //Send();
        }
    }
}
同宿舍的主机(即IP前三个完全一样)就能收到,但IP 如59.68.192 .* 和59.68.198.*的机子就只能收到自己发的数据二不能收到对方的,为什么