Imports System.Net
Imports System.Net.Sockets
Imports System.Threading
Public Class Form1
    Private Chat As Chat
    Private thread As Thread

    Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
        thread.Abort()
        Chat.Close()
    End Sub
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        'vs05在新加的功能窗体控件的线程安全，即只有创建控件的线程才可以对线程操作。
        '但是很多时候我们需要跨线程操作例如本例，下面是最简单的处理方法。
        CheckForIllegalCrossThreadCalls = False    '允许跨线程操作窗体

        '由于本人是用一台机器测试的所以可以自己发送自己接收，如果两台用两台机器做可以通过其它途径设置IP和端口
        Chat = New Chat("8000", "127.0.0.1", AddressOf receive)

        AddHandler Chat.GetMessageEvent, AddressOf receive
        '启动线程侦听接收信息
        thread = New Thread(AddressOf Chat.Receive)
        thread.Start()
    End Sub
    Private Sub send(ByVal message As String)
        Chat.Send(message)
        'MessageBox.Show(message)
    End Sub
    Private Sub receive(ByVal message As String)
        '将收到的信息显示出来，仅此而以
        RTB.AppendText(message)
    End Sub

    Private Sub btnSend_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSend.Click
        '读者可以通过一个文本框来输入要发送的信息，这里本人懒得写。
        Chat.Send("aaa" + Chr(13))
    End Sub
End Class
Class Chat
    Private m_Port As String     '端口
    Private m_IP As String       'IP
    Private m_UDPClient As UdpClient
    Private m_RIEP As IPEndPoint '终端
    Private m_ReFunction As ReceiveMessage  '委托变量
#Region "属性"
    ''' <summary>
    ''' 对方端口
    ''' </summary>
    ''' <value></value>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Property Port() As String
        Get
            Return m_Port
        End Get
        Set(ByVal value As String)
            m_Port = value
        End Set
    End Property
    ''' <summary>
    ''' 对方IP
    ''' </summary>
    ''' <value></value>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Property IP() As String
        Get
            Return m_IP
        End Get
        Set(ByVal value As String)
            m_IP = value
        End Set
    End Property
    ''' <summary>
    ''' 委托方法
    ''' </summary>
    ''' <value></value>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Property ReFunction() As ReceiveMessage
        Get
            Return m_ReFunction
        End Get
        Set(ByVal value As ReceiveMessage)
            m_ReFunction = value
        End Set
    End Property
#End Region

#Region "事件委托"
    '通过事件和委托两种方法实现 信息的接收
    Public Event GetMessageEvent(ByVal Message As String)
    Public Delegate Sub ReceiveMessage(ByVal message As String)
#End Region

#Region "构造函数"
    Sub New(ByVal f As ReceiveMessage)
        m_Port = "8000"
        m_IP = "127.0.0.1"
        m_ReFunction = f
        m_RIEP = New IPEndPoint(IPAddress.Parse(m_IP), Convert.ToInt32(m_Port))
        m_UDPClient = New UdpClient(m_RIEP)
    End Sub
    Sub New(ByVal p As String, ByVal i As String, ByVal f As ReceiveMessage)
        m_Port = p
        m_IP = i
        m_ReFunction = f
        m_RIEP = New IPEndPoint(IPAddress.Parse(m_IP), Convert.ToInt32(m_Port))
        m_UDPClient = New UdpClient(m_RIEP)
    End Sub
#End Region

#Region "方法"
    ''' <summary>
    ''' 发送消息
    ''' </summary>
    ''' <param name="message"></param>
    ''' <remarks></remarks>
    Public Sub Send(ByVal message As String)
        Dim sendBytes() As Byte = System.Text.Encoding.BigEndianUnicode.GetBytes(message.ToCharArray())
        Try
            Connect()
            m_UDPClient.Send(sendBytes, sendBytes.Length)
        Catch ex As Exception
            Throw ex
        End Try
    End Sub
    ''' <summary>
    ''' 接收信息
    ''' </summary>
    ''' <remarks></remarks>
    Public Sub Receive()
        Dim selfIEP As IPEndPoint = New IPEndPoint(IPAddress.Any, 0)
        While True
            Dim receiveBytes() As Byte
            Try
                receiveBytes = m_UDPClient.Receive(selfIEP)
            Catch ex As Exception
                Throw ex
            End Try
            Dim receiveStr As String = System.Text.Encoding.BigEndianUnicode.GetString(receiveBytes)
            m_ReFunction(receiveStr)
            '触发事件 出可以激活下面的方法，但是要隐掉上一句
            'RaiseEvent GetMessageEvent(receiveStr)
        End While
    End Sub
    ''' <summary>
    ''' 连接对方
    ''' </summary>
    ''' <remarks></remarks>
    Public Sub Connect()
        Try
            m_UDPClient.Connect(m_RIEP)
        Catch ex As Exception
            Throw ex
        End Try
    End Sub
    ''' <summary>
    ''' 关闭连接
    ''' </summary>
    ''' <remarks></remarks>
    Public Sub Close()
        m_UDPClient.Close()
        m_UDPClient = Nothing
    End Sub
#End Region
End Class

在群43255191中有源文件可以下载，功能和界面将会完善。并实现聊天室功能。