C# 广播问题

Client
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Net;
using System.Net.Sockets;namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }        private void button1_Click(object sender, EventArgs e)
        {
            this.Send();
        }
        public void Send()
        {
            try
            {
                Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
                //IPAddress br = Dns.GetHostAddresses("000000")[0];
                IPEndPoint ep = new IPEndPoint(IPAddress.Broadcast, 1984);//
                byte[] sendbuf = Encoding.GetEncoding("gb2312").GetBytes("000000");
                //IPEndPoint ep = new IPEndPoint(br, 1984);
                s.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.Broadcast, 1);
                s.SendTo(sendbuf, ep);
                           }
            catch { MessageBox.Show(""); }
            
        }
    }
}Server
using System;
using System.Collections.Generic;
using System.Text;
using System.Net;
using System.Net.Sockets;
using System.Windows.Forms;
namespace WindowsApplication2
{
    public class SSocket
    {
        bool done = false;
        private const int listPort = 1984;//设置端口
        IPEndPoint groupEP;
        internal void StartListent()
        {
            UdpClient listent = new UdpClient(listPort);
            groupEP = new IPEndPoint(IPAddress.Any, listPort);
            try
            {
                //while (!done)
                //{
                    listent.BeginReceive(new AsyncCallback(IAsyncResult), listent);
                //}
            }
            catch (Exception er)
            {
                MessageBox.Show(er.Message);
            }
            //listent.Close();
        }
        private void IAsyncResult(IAsyncResult xx)
        {
            UdpClient by = (UdpClient)xx.AsyncState;
            byte[] bys = by.Receive(ref groupEP);
            //string EIP;
            string strinfo = Encoding.GetEncoding("gb2312").GetString(bys, 0, bys.Length);
            MessageBox.Show(strinfo);
            by.Close();
            StartListent();
        }
    }
}出现的问题是,Client需要点击botton1两次Server才监听得到~不知道是那里出错了,请教一下,刚刚学习不久