I am trying to get a good grasp of UDP on Android, so I am writing a small test program to set up 2 sockets on the same machine, send a packet and receive it. I thought it would be straight-forward, but something is going wrong. My code is:
DatagramSocket server; DatagramSocket client; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); // Initialize a client socket and a server socket using UDP try { server = new DatagramSocket(); client = new DatagramSocket(); } catch (SocketException e) { // TODO Auto-generated catch block e.printStackTrace(); } // Server will now send some data String data = "This is a test"; DatagramPacket sendPacket = new DatagramPacket(data.getBytes(), data.length(), client.getInetAddress(), client.getLocalPort()); try { server.send(sendPacket); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } // Client has to receive and read the data byte[] buf = new byte[1024]; DatagramPacket receivePacket = new DatagramPacket(buf, buf.length); try { client.receive(receivePacket); byte[] receivedData = receivePacket.getData(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } server.disconnect(); client.disconnect(); } When I debug my code, it goes into the last try, in "client.receive(receivePacket);" but it never comes back from that function call. The packet seems to be never received, but I have a hard time finding why that is.
I hope someone could please help me fix this problem.
EDIT: New code using threads. Calling "recieve" before actually sending the packet. Trying to use AsyncTask.
public class udpexample extends Activity { DatagramSocket server; DatagramSocket client; String data = "This is a test"; private static final String TAG = "UDPExampleActivity"; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Log.i(TAG, "Starting"); // Initialize a client socket and a server socket using UDP try { server = new DatagramSocket(); client = new DatagramSocket(); } catch (SocketException e) { // TODO Auto-generated catch block e.printStackTrace(); } new ReceivePacket().execute(); try { Thread.sleep(2000); } catch (InterruptedException e1) { // TODO Auto-generated catch block e1.printStackTrace(); } // Server will now send some data DatagramPacket sendPacket = new DatagramPacket(data.getBytes(), data.length(), client.getInetAddress(), client.getLocalPort()); try { Log.i(TAG, "About to send"); server.send(sendPacket); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } private class ReceivePacket extends AsyncTask<Void, Void, Void> { // Thread used to receive a packet @Override protected Void doInBackground(Void... params) { // Client has to receive and read the data byte[] buf = new byte[1024]; DatagramPacket receivePacket = new DatagramPacket(buf, buf.length); try { Log.i(TAG, "About to receive"); client.receive(receivePacket); byte[] receivedData = receivePacket.getData(); // Verify that the packet is identical to the one being sent } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } return null; } protected void onPostExecute(Void result) { server.disconnect(); client.disconnect(); } } } Still having the same issue, it stops and waits on receive and nothing happens.
Thank you very much,
Jary
