Simple udp server for android and receiving multiple messages

Question

I am writing a simple method for udp server:

private void runUdpServer() { String message; byte[] lmessage = new byte[MAX_UDP_DATAGRAM_LEN]; DatagramPacket packet = new DatagramPacket(lmessage, lmessage.length); DatagramSocket socket = null; try { socket = new DatagramSocket(UDP_SERVER_PORT); socket.receive(packet); message = new String(lmessage, 0, packet.getLength()); textMessage.setText(message); } catch (SocketException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { if (socket != null) { socket.close(); } } } 

How can I start this server and listen to messages. I use this method in onCreate, but when I send a message from the client, I saw this message, but when I send the second message, I do not see this second. Only this is the first message. How can I do to receive new messages?

Edit: This is my code now:

 @SuppressLint("NewApi") public class Server extends Activity { private static final int UDP_SERVER_PORT = 2004; private static final int MAX_UDP_DATAGRAM_LEN = 1500; private TextView textMessage; private RunServerInThread runServer = null; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_server); if (android.os.Build.VERSION.SDK_INT > 9) { StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build(); StrictMode.setThreadPolicy(policy); } textMessage = (TextView) findViewById(R.id.messageText); runServer = new RunServerInThread(); runServer.start(); } private Runnable updateTextMessage = new Runnable() { public void run() { if (runServer == null) return; textMessage.setText(runServer.getLastMessage()); } }; @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.server, menu); return true; } private void runUdpServer() { String message; byte[] lmessage = new byte[MAX_UDP_DATAGRAM_LEN]; DatagramPacket packet = new DatagramPacket(lmessage, lmessage.length); DatagramSocket socket = null; try { socket = new DatagramSocket(UDP_SERVER_PORT); socket.receive(packet); message = new String(lmessage, 0, packet.getLength()); textMessage.setText(message); } catch (SocketException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { if (socket != null) { socket.close(); } } } private class RunServerInThread extends Thread{ private boolean keepRunning = true; private String lastmessage = ""; @Override public void run() { String message; byte[] lmessage = new byte[MAX_UDP_DATAGRAM_LEN]; DatagramPacket packet = new DatagramPacket(lmessage, lmessage.length); DatagramSocket socket = null; while(keepRunning){ try { socket = new DatagramSocket(UDP_SERVER_PORT); socket.receive(packet); message = new String(lmessage, 0, packet.getLength()); textMessage.setText(message); } catch (SocketException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { if (socket != null) { socket.close(); } } } } public String getLastMessage() { return lastmessage; } } } 

and I get an error:

 05-30 12:18:48.562: E/AndroidRuntime(17987): FATAL EXCEPTION: Thread-1233 05-30 12:18:48.562: E/AndroidRuntime(17987): android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views. 05-30 12:18:48.562: E/AndroidRuntime(17987): at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:4746) 05-30 12:18:48.562: E/AndroidRuntime(17987): at android.view.ViewRootImpl.requestLayout(ViewRootImpl.java:823) 05-30 12:18:48.562: E/AndroidRuntime(17987): at android.view.View.requestLayout(View.java:15469) 05-30 12:18:48.562: E/AndroidRuntime(17987): at android.view.View.requestLayout(View.java:15469) 05-30 12:18:48.562: E/AndroidRuntime(17987): at android.view.View.requestLayout(View.java:15469) 05-30 12:18:48.562: E/AndroidRuntime(17987): at android.view.View.requestLayout(View.java:15469) 05-30 12:18:48.562: E/AndroidRuntime(17987): at android.widget.RelativeLayout.requestLayout(RelativeLayout.java:318) 05-30 12:18:48.562: E/AndroidRuntime(17987): at android.view.View.requestLayout(View.java:15469) 05-30 12:18:48.562: E/AndroidRuntime(17987): at android.widget.TextView.checkForRelayout(TextView.java:6368) 05-30 12:18:48.562: E/AndroidRuntime(17987): at android.widget.TextView.setText(TextView.java:3622) 05-30 12:18:48.562: E/AndroidRuntime(17987): at android.widget.TextView.setText(TextView.java:3480) 05-30 12:18:48.562: E/AndroidRuntime(17987): at android.widget.TextView.setText(TextView.java:3455) 05-30 12:18:48.562: E/AndroidRuntime(17987): at pl.udpconnection.server.Server$RunServerInThread.run(Server.java:89) 

How can I solve this problem?

Answer 1

Put the code you have in the loop and put this loop in your own thread so that it does not block the user interface thread.

Use runOnUiThread () to update the user interface from this new thread.

Example:

 private MyDatagramReceiver myDatagramReceiver = null; protected void onResume() { myDatagramReceiver = new MyDatagramReceiver(); myDatagramReceiver.start(); } protected void onPause() { myDatagramReceiver.kill(); } private class MyDatagramReceiver extends Thread { private boolean bKeepRunning = true; private String lastMessage = ""; public void run() { String message; byte[] lmessage = new byte[MAX_UDP_DATAGRAM_LEN]; DatagramPacket packet = new DatagramPacket(lmessage, lmessage.length); try { DatagramSocket socket = new DatagramSocket(UDP_SERVER_PORT); while(bKeepRunning) { socket.receive(packet); message = new String(lmessage, 0, packet.getLength()); lastMessage = message; runOnUiThread(updateTextMessage); } } catch (Throwable e) { e.printStackTrace(); } if (socket != null) { socket.close(); } } public void kill() { bKeepRunning = false; } public String getLastMessage() { return lastMessage; } } private Runnable updateTextMessage = new Runnable() { public void run() { if (myDatagramReceiver == null) return; textMessage.setText(myDatagramReceiver.getLastMessage()); } };