Question

Possible Duplicate:
android.os.NetworkOnMainThreadException

When I try to run my 2nd Activity from a Listener on the 1st Activity, main.xml has a fatal exception. When I take out the runTcpClient(); on the TcpClient Thread() it loads up fine.

I came across UI threads managing using aSyncTask: Android UI aSyncTask

CODE FOR TcpClientJava.java

package com.mesger;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.Socket;
import java.net.UnknownHostException;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;



public class TcpClient extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    runTcpClient();
    finish();
}

private static final int TCP_SERVER_PORT = 1234;
private void runTcpClient() {
    try {
        Socket s = new Socket("10.0.2.2", TCP_SERVER_PORT);
        BufferedReader in = new BufferedReader(new InputStreamReader(s.getInputStream()));
        BufferedWriter out = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
        //send output msg
        String outMsg = "TCP connecting to " + TCP_SERVER_PORT + System.getProperty("line.separator"); 
        out.write(outMsg);
        out.flush();
        Log.i("TcpClient", "sent: " + outMsg);
        //accept server response
        String inMsg = in.readLine() + System.getProperty("line.separator");
        Log.i("TcpClient", "received: " + inMsg);
        //close connection
        s.close();
    } catch (UnknownHostException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } 
}
//replace runTcpClient() at onCreate with this method if you want to run tcp client as a service
private void runTcpClientAsService() {
    Intent lIntent = new Intent(this.getApplicationContext(), TcpClientService.class);
    this.startService(lIntent);
}

}

LOGCAT

11-12 13:41:22.725: D/gralloc_goldfish(738): Emulator without GPU emulation detected.
11-12 13:42:32.409: D/AndroidRuntime(738): Shutting down VM
11-12 13:42:32.409: W/dalvikvm(738): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
11-12 13:42:32.465: E/AndroidRuntime(738): FATAL EXCEPTION: main
11-12 13:42:32.465: E/AndroidRuntime(738): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.i911.emergency.response/com.mesger.TcpClient}: android.os.NetworkOnMainThreadException
11-12 13:42:32.465: E/AndroidRuntime(738):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
11-12 13:42:32.465: E/AndroidRuntime(738):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
11-12 13:42:32.465: E/AndroidRuntime(738):  at android.app.ActivityThread.access$600(ActivityThread.java:130)
11-12 13:42:32.465: E/AndroidRuntime(738):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
11-12 13:42:32.465: E/AndroidRuntime(738):  at android.os.Handler.dispatchMessage(Handler.java:99)
11-12 13:42:32.465: E/AndroidRuntime(738):  at android.os.Looper.loop(Looper.java:137)
11-12 13:42:32.465: E/AndroidRuntime(738):  at android.app.ActivityThread.main(ActivityThread.java:4745)
11-12 13:42:32.465: E/AndroidRuntime(738):  at java.lang.reflect.Method.invokeNative(Native Method)
11-12 13:42:32.465: E/AndroidRuntime(738):  at java.lang.reflect.Method.invoke(Method.java:511)
11-12 13:42:32.465: E/AndroidRuntime(738):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
11-12 13:42:32.465: E/AndroidRuntime(738):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-12 13:42:32.465: E/AndroidRuntime(738):  at dalvik.system.NativeStart.main(Native Method)
11-12 13:42:32.465: E/AndroidRuntime(738): Caused by: android.os.NetworkOnMainThreadException
11-12 13:42:32.465: E/AndroidRuntime(738):  at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1117)
11-12 13:42:32.465: E/AndroidRuntime(738):  at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:84)
11-12 13:42:32.465: E/AndroidRuntime(738):  at libcore.io.IoBridge.connectErrno(IoBridge.java:127)
11-12 13:42:32.465: E/AndroidRuntime(738):  at libcore.io.IoBridge.connect(IoBridge.java:112)
11-12 13:42:32.465: E/AndroidRuntime(738):  at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:192)
11-12 13:42:32.465: E/AndroidRuntime(738):  at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
11-12 13:42:32.465: E/AndroidRuntime(738):  at java.net.Socket.startupSocket(Socket.java:566)
11-12 13:42:32.465: E/AndroidRuntime(738):  at java.net.Socket.tryAllAddresses(Socket.java:127)
11-12 13:42:32.465: E/AndroidRuntime(738):  at java.net.Socket.<init>(Socket.java:177)
11-12 13:42:32.465: E/AndroidRuntime(738):  at java.net.Socket.<init>(Socket.java:149)
11-12 13:42:32.465: E/AndroidRuntime(738):  at com.mesger.TcpClient.runTcpClient(TcpClient.java:32)
11-12 13:42:32.465: E/AndroidRuntime(738):  at com.mesger.TcpClient.onCreate(TcpClient.java:25)
11-12 13:42:32.465: E/AndroidRuntime(738):  at android.app.Activity.performCreate(Activity.java:5008)
11-12 13:42:32.465: E/AndroidRuntime(738):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
11-12 13:42:32.465: E/AndroidRuntime(738):  at     android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
11-12 13:42:32.465: E/AndroidRuntime(738):  ... 11 more

Answer 1

Caused by: android.os.NetworkOnMainThreadException

You are trying to perform a potentially slow network operation on the main thread, this became a fatal exception in Android 3.0+. Simply move runTcpClient() to a new Thread by using an AsyncTask or Loader.

Here is an example: How to fix android.os.NetworkOnMainThreadException?.

---

Try this:

class TcpClientTask extends AsyncTask<Void, Void, Void> {
    private static final int TCP_SERVER_PORT = 1234;
    private boolean error = false;

    protected Void doInBackground(Void... arg0) {
        try {
            Socket s = new Socket("10.0.2.2", TCP_SERVER_PORT);
            BufferedReader in = new BufferedReader(new InputStreamReader(s.getInputStream()));
            BufferedWriter out = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
            //send output msg
            String outMsg = "TCP connecting to " + TCP_SERVER_PORT + System.getProperty("line.separator"); 
            out.write(outMsg);
            out.flush();
            Log.i("TcpClient", "sent: " + outMsg);
            //accept server response
            String inMsg = in.readLine() + System.getProperty("line.separator");
            Log.i("TcpClient", "received: " + inMsg);
            //close connection
            s.close();
        } catch (UnknownHostException e) {
            error = true;
            e.printStackTrace();
        } catch (IOException e) {
            error = true;
            e.printStackTrace();
        }
        return null;
    }

    protected void onPostExecute() {
        if(error) {
            // Something bad happened
        }
        else {
            // Success
        }

    }
}

To use it call: new TcpClientTask().execute();

---

I have 1 more question. String inMsg = in.readLine() + System.getProperty("line.separator"); which receives messages, how would I set it up to get it every 15ms or whatever is stable to keep receiving data.

I’m not certain what you are trying to do. But I noticed you only call readLine() once, if you want to read more than one line, use a loop:

StringBuilder msg = new StringBuilder();
String line;
while((line = in.readLine()) != null) // Keep reading until the end of the file is reached
    msg.append(in.readLine()).append(System.getProperty("line.separator"));

StringBuilders create less overhead when adding Strings together, simply use msg.toString() when you want get the whole message.