How can I get the data from a thread that acts as a UDP server?

Question

I am making an Android application that receives messages from an Arduino, I implemented a UDP server opening a Thread, but I can not get the value of the answer string "lastMessage", because with this value I will make a series of actions.

This is my class served_UDP:

public class Servidor_UDP {
    private boolean server_activado = true;
    private String lastMessage = "";
    DatagramSocket socket;
    private byte[] resp;
    private DatagramPacket pqtResp;
    Servidor_UDP()
    {
        resp = new byte[1024];
        try {
            socket = new DatagramSocket(6000);
            pqtResp = new DatagramPacket(resp, resp.length);
        } catch (SocketException e) {
            e.printStackTrace();
        }
    }

    public void start(){
        Thread t = new Thread(new server());
        t.start();
    }

    public class server implements Runnable {
        server() { run(); }
        public void run() {
            String message = "";
            try {
                do
                {
                    socket.receive(pqtResp);
                    //message = new String(resp).trim();
                    message = new String(pqtResp.getData(),0,pqtResp.getLength());
                    lastMessage = message;
                } while(server_activado);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public String getString() 
    {
        return lastMessage;
    }

    public void setServer(boolean b)
    {
        server_activado = b;
    }
}

This class I implemented from the onCreate of my MainActivity:

Servidor_UDP UDP_S;
UDP_S = new Servidor_UDP();
UDP_S.start();

I try to get the results of a method of the main class and show them in a TextView to make sure that the messages are arriving but it does not show me anything, just empty.

public void actualizarUI()
{
    respuesta = UDP_S.getString();
    txt.setText(respuesta);
}

I await your help, thanks in advance.

Answer 1

Your server() constructor should not call run(). Thread.start() will do that. At present Thread.start() is never executing, let alone completing, so any code that calls your start() method will never return.