C# Receiving UDP data

Question

I am trying to learn UDP socket programming in C#. I have made a WinForm that will send the data, the code is listed below. It's a small form with three text boxes and a button.

using System;
using System.Text;
using System.Windows.Forms;
using System.Net;
using System.Net.Sockets;

namespace UDP_example

{
    public partial class Form1 : Form1
    {
    public Form1()
    {
        InitializeComponent();
    }

    private void btnSend_Click(object sender, EventArgs e)
    {
        // make sure all text boxes contain data, or do nothing.
        if (string.IsNullOrEmpty(txtIP.Text)) return;
        if (string.IsNullOrEmpty(txtPort.Text)) return;
        if (string.IsNullOrEmpty(txtMessage.Text)) return;

        // convert the text into byte array
        byte[] message = Encoding.ASCII.GetBytes(txtMessage.Text);
        string ipAddress = txtIP.Text;
        int sendPort = Convert.ToInt32(txtPort.Text);

        // send the data
        try
        {
            using (var client = new UdpClient())
            {
                IPEndPoint server = new IPEndPoint(IPAddress.Parse(ipAddress), sendPort);
                client.Connect(server);
                client.Send(message, message.Length);
            }
        }
        // display error if one occurs
        catch (Exception exc)
        {
            MessageBox.Show(exc.Message);
        }

        // clean up
        txtMessage.Clear();
        txtMessage.Focus();
    }
}

This part appears to work fine. What I need is to display the received data in a textbox or a messagebox on the other side of the connection.

Can someone show me how to do that? I don't know how to basically get the socket to listen with async and display incoming data on the receiving side. It would be just a form one with textbox or a single messagebox that displays incoming data.

EDIT: This is the receive code, but I want it to receive from any IP address, not just the local. (Found and modified this code snippet.)

using System;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Net;
using System.Net.Sockets;

namespace UDP_Server
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            System.Threading.ThreadPool.QueueUserWorkItem(new System.Threading.WaitCallback(ConnectUDP));
        }

        private void ConnectUDP(object state)
        {
            UdpClient subscriber = new UdpClient(4345);
            IPAddress addr = IPAddress.Parse("127.0.0.1");
            subscriber.JoinMulticastGroup(addr);
            IPEndPoint ep = null;

            byte[] pdata = subscriber.Receive(ref ep);
            string rdata = Encoding.ASCII.GetString(pdata);
            txtReceived.Text += rdata;
        }
    }
}

I've been reading a lot of samples today and watching some videos on YouTube, but I'm fairly stuck in what I thought would be very simple. My only requirement is that it puts the received data from the UDP port into a textbox. Thanks for any help.

Answer 1

As mentioned from @JuanR you would need something like this on your server side

// This constructor arbitrarily assigns the local port number.
UdpClient udpClient = new UdpClient(yourUDPPort);

//IPEndPoint object will allow us to read datagrams sent from any source.
IPEndPoint RemoteIpEndPoint = new IPEndPoint(IPAddress.Any, 0);

// Blocks until a message returns on this socket from a remote host.
Byte[] receiveBytes = udpClient.Receive(ref RemoteIpEndPoint); 
string returnData = Encoding.ASCII.GetString(receiveBytes);