Calling a function when UDP data recieved.

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Hi there, still not mature in c# programming, i have written an application in which it receives data from arduino using UDP protocol, when i click a button data is sent and received without hurdle, but i want my application to receive data automatically when arduino sends it. so that i wont click any button or i dont have to trigger any events manually. here is the total code. PS im using Visual Studio 2010 Express.

is there a way to receive data only when arduino sends it?
please help

What I have tried:

C#

private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                Socket SOCK = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
                SOCK.ReceiveTimeout = 2000;
                SOCK.SendTimeout = 2000;
                IPAddress serverAddres = IPAddress.Parse("192.168.1.177");
                IPEndPoint endPoint = new IPEndPoint(serverAddres, 23);
                String text = textBox1.Text;
                byte[] sendBuffer = Encoding.ASCII.GetBytes(text);
                SOCK.SendTo(sendBuffer, endPoint);
                byte[] recievedByte = new byte[1024];
                int bytesrec = SOCK.Receive(recievedByte);
                textBox1.Text = Encoding.UTF8.GetString(recievedByte, 0, bytesrec);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message,"Error", MessageBoxButtons.RetryCancel, MessageBoxIcon.Error);
            }

        }

Posted 20-Nov-18 19:50pm

Engr.Shah

Updated 20-Nov-18 21:52pm

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Afzaal Ahmad Zeeshan · Accepted Answer · 2018-11-20T21:52:00

You need to attach the async callback¹, that receives the data for your socket, on its behalf and then alerts you that data has been received. You cannot attach a receive function, as it might be blocking. You can argue, that,

C#

// Your receive call is useless as well, and so would be this, 
SOCK.Receive(buffer, offset, SOCK.Available, SocketFlags.None);

would read the bytes, but no, because even in this case, Available will be 0 as the device might have not yet sent a message, thus it will return, acting as a non-blocking call. A good approach is to use a callback, and do a BeginReceive(...), and asynchronously read from the wire,

C#

// Code from Microsoft documentations
// Begin receiving the data from the remote device.  
client.BeginReceive( state.buffer, 0, StateObject.BufferSize, 0,  
     new AsyncCallback(ReceiveCallback), state);

Please review this documentation to learn a bit more on the topic, Asynchronous Client Socket Example | Microsoft Docs[^], and if you are writin this as a server application, then go through this, Asynchronous Server Socket Example | Microsoft Docs[^]

1. I italicized that, because it is funny to consider a callback, and asynchronous approach in 21st century.