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VB.net基础:使用UDP发送和接收消息

答案:Imports System.Net

Imports System.Threading

Imports System.Text

Imports System.Net.Sockets



Module Module1



Dim PortNumber As Integer = 1984 '侦听端口号

Dim Cmd As String = "Chat:" '提示符

Dim listener As Socket '侦听socket

Dim tListener As Thread '侦听线程

Dim Prompted As Boolean = False '用于线程间同步的标志变量



Sub Main()

Welcome() '欢迎信息

StartListener() '开始侦听

StartChatting() '准备好让用户发送消息

End Sub



Private Sub Welcome()

Dim txtMessage As String = vbCrLf & "Welcome! I am a console application for LAN chatting." & vbCrLf

Console.WriteLine(txtMessage)

End Sub



Private Sub StartListener()

Dim ready As Boolean = False

Dim LocalPoint As IPEndPoint

Dim msg As String



While Not ready '向用户询问侦听端口号。用户可以直接回车,表示选择默认的。

msg = GetParams("===Now, enter the local port you want to listen(" & PortNumber & "):")

If msg = "" Then msg = PortNumber

Try

PortNumber = Int(msg)

LocalPoint = New IPEndPoint(Dns.GetHostByName(Dns.GetHostName).AddressList(0), PortNumber)

listener = New Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp)

listener.Bind(LocalPoint)

ready = True

Catch ex As Exception

Console.WriteLine("※※※ERROR※※※ " & vbCrLf & ex.Message & vbCrLf)

End Try

End While



tListener = New Thread(AddressOf thrListener)

tListener.Start()

End Sub



Private Sub StartChatting()

Dim RemoteHost As String = Dns.GetHostName

Dim RemotePort As Integer = 1984

Dim RemotePoint As IPEndPoint

Dim ready As Boolean = False

Dim msg As String



While Not ready '向用户询问发送消息的目标主机和端口。用户可以直接回车,表示选择默认的。

msg = GetParams("---enter the name of the one you want to chat with(" & RemoteHost & "):")

If Not msg = "" Then RemoteHost = msg

msg = GetParams("---enter the port number that guy listening at(" & RemotePort & "):")

If msg = "" Then msg = RemotePort

Try

RemotePort = Int(msg)

RemotePoint = New IPEndPoint(Dns.GetHostByName(RemoteHost).AddressList(0), RemotePort)

ready = True

Catch ex As Exception

Console.WriteLine("※※※ERROR※※※ " & vbCrLf & ex.Message & vbCrLf)

End Try

End While



Console.WriteLine()

Console.WriteLine("OK, now you can chat. Type ""help"" to find out what you can do.")

Console.WriteLine()



Dim sender As New UdpClient

Dim Message As String = Prompt()

While True '用户现在可以开始发送消息

Prompted = False

Select Case Message.ToLower

Case "exit"

Exit While

Case "help"

ShowHelp()

Case Else

Dim ByArr As Byte() = Encoding.Unicode.GetBytes(Message)

sender.Send(ByArr, ByArr.Length, RemotePoint) '发出消息

End Select

Message = Prompt()

End While



tListener.Abort()

End

End Sub



Private Function GetParams(ByVal Msg As String) As String

Console.Write(Msg)

Return Console.ReadLine

End Function



Private Function Prompt() As String

If Not Prompted Then

Console.Write(Cmd)

Prompted = True

End If

Return Console.ReadLine

End Function





Private Sub thrListener() '侦听线程

Dim bytes(4096) As Byte

Dim NumGet As Integer

Dim Msg As String



While True

Debug.WriteLine("Waiting for a message...")

NumGet = listener.Receive(bytes) '接收

Prompted = False

Msg = Encoding.Unicode.GetString(bytes, 0, NumGet) '与发送消息一样使用unicode编码

Console.WriteLine(vbCrLf & ">>>>>>>>>" & Msg & vbCrLf)

If Not Prompted Then

Console.Write(Cmd)

Prompted = True

End If

End While

End Sub



Private Sub ShowHelp()

Console.WriteLine("")

Console.WriteLine("========================================================================")

Console.WriteLine("This program is very simple, you can type ""exit"" to exit program.")

Console.WriteLine("========================================================================")

Console.WriteLine("")

End Sub



End Module




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