vb.net UDP广播显示来自发件人的IP

Question

我正在发送带有消息“你好？”的 UDP 广播。使用此代码：

    Public Sub UDPSendHello()

    Dim client As New UDPClient()
    Dim ip As New IPEndPoint(IPAddress.Broadcast, 15000)

    Dim bytes As Byte() = Encoding.ASCII.GetBytes("Hello?")
    client.Send(bytes, bytes.Length, ip)
    client.Close()
End Sub

当然，UDPListner 可以正常接收消息！

  Private ReadOnly udp As New UdpClient(15000)
    Public Sub UDPHelloListner()
        udp.BeginReceive(AddressOf Receive, New Object())
    End Sub
    Private Sub Receive(ByVal ar As IAsyncResult)
        Dim ip As New IPEndPoint(IPAddress.Any, 15000)
        Dim bytes As Byte() = udp.EndReceive(ar, ip)
        Dim message As String = Encoding.ASCII.GetString(bytes)
        If message = "Hello?" Then
            Dim sender As New IPEndPoint(IPAddress.Any, 15000)
            Dim senderRemote As EndPoint = CType(sender, EndPoint)

            MessageBox.Show("I see message, Hello")
        End If

        UDPHelloListner()
    End Sub

那么我怎样才能获得发件人的 IP 地址并将其显示在消息框、文本框等中。

我看到了Socket.RecieveFrom 方法，但是！在以下代码的这一点上，我收到此错误"The system detected an invalid pointer address in attempting to use a pointer argument in a call"，“s.ReceiveFrom(msg, SocketFlags.None, senderRemote)”

   Public Sub ReceiveFrom2()
        Dim hostEntry As IPHostEntry = Dns.GetHostEntry(Dns.GetHostName())
        Dim endPoint As New IPEndPoint(hostEntry.AddressList(0), 11000)

        Dim s As New Socket(EndPoint.Address.AddressFamily, SocketType.Dgram, ProtocolType.Udp)

        ' Creates an IpEndPoint to capture the identity of the sending host. 
        Dim sender As New IPEndPoint(IPAddress.Any, 0)
        Dim senderRemote As EndPoint = CType(sender, EndPoint)

        ' Binding is required with ReceiveFrom calls.
        s.Bind(endPoint)

        Dim msg() As Byte = New [Byte](255) {}
        Console.WriteLine("Waiting to receive datagrams from client...")
        ' This call blocks. 
        s.ReceiveFrom(msg, SocketFlags.None, senderRemote)
        s.Close()

    End Sub 'ReceiveFrom2

那么我将如何获取发件人 IP 并使用上面的代码在文本框、消息等中显示它......????

Answer 1

BeginReceive 是一个异步调用。在致电BeginReceive 之前，您需要设置您的 udp 连接。我不是很了解vb.net（我用的是C#），但你需要使用大致像这样的东西：

Public Class UdpState
   Public e As IPEndPoint
   Public u As UdpClient
End Class

Public Shared messageReceived As Boolean = False

Public Sub UDPHelloListner()
    Dim ip As New IPEndPoint(IPAddress.Any, 15000)
    Dim udp As New UdpClient(ip)

    Dim state As New UdpState()
    state.e = ip
    state.u = udp

    udp.BeginReceive(new AsyncCallback(AddressOf Receive), state)

    Do While Not messageReceived
        Thread.Sleep(100)
    Loop
End Sub

Private Sub Receive(ByVal ar As IAsyncResult)
    Dim udp As UdpClient = CType((CType(ar.AsyncState, UdpState)).u, UdpClient)
    Dim ip As IPEndPoint = CType((CType(ar.AsyncState, UdpState)).e, IPEndPoint)

    Dim bytes As Byte() = udp.EndReceive(ar, ip)
    Dim message As String = Encoding.ASCII.GetString(bytes)
    If message = "Hello?" Then
        MessageBox.Show("I see message, Hello from {0}", ip.Address.ToString())
        messageReceived = True
    End If
End Sub

Answer 2

我需要做的就是使用 IPEndPoint.ToString 方法： http://msdn.microsoft.com/en-us/library/system.net.ipendpoint.tostring.aspx