[Java for Android App Development] flavglen:
Hi frends im working on my android final year project based on sockets..im using ssynctask to connect socket etc..Everything works fine, since I'm using AsyncTask to create a Socket connection ... the socket works fine in the doInBackground() method, but when I try to send Sensor data from theonSensorChanged() method, I get null pointer exception. I don't know what went wrong. in short Socket returns NULL outside asyncTask Class...can some 1 help me ?..

here is my code

package com.example.sensorsmart;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

import android.app.Activity;
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity implements SensorEventListener{

private static final int SERVERPORT = 8222;
private static final String SERVER_IP = "192.168.0.101";
private SensorManager mSensorManager;
private Sensor mAccelerometer;
private TextView tv ;
public ServerSocket serverSocket=null;
public Socket socket = null;
public BufferedReader in ;
public BufferedWriter out;
public PrintWriter pw ;
public FileWriter writer=null;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new MyTask().execute();
mSensorManager = (SensorManager)getSystemService(Context.SENSOR_SERVICE);
mAccelerometer mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
mSensorManager.registerListener(this, mAccelerometer,SensorManager.SENSOR_DELAY_NORMAL);

}
public void onStopClick(View view) {
mSensorManager.unregisterListener(this);}

private class MyTask extends AsyncTask<Void, Void, Void>
{
@Override
protected Void doInBackground(Void... arg0) {

try {
serverSocket = new ServerSocket(8222);
} catch (IOException e) {
e.printStackTrace();
}
try {
socket=serverSocket.accept();
Log.i("TcpServer", "CONNECTED");
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
pw = new PrintWriter(socket.getOutputStream(),true);
if(!in.ready())
{
Log.i("TcpServer", "READER IS NOT READY");
}

final String g;
final String c;
String b = null;
Log.i("TcpServer", "GOING");
g=in.readLine();
runOnUiThread(new Runnable() {
public void run() {
Toast.makeText(getApplicationContext(),g, Toast.LENGTH_LONG).show();
}
});

} catch (IOException e) {
e.printStackTrace();
String response = e.getCause().toString();
Log.i("TCP",response);
}
return null;
}

}

@Override
public void onSensorChanged(SensorEvent event) {
float x = event.values[0];
float y = event.values[1];
float z = event.values[2];
pw.write("g"); //NULL POINT EXCEPTION THROWS HERE
}
}

LOGCAT:

02-06 11:31:54.250: E/AndroidRuntime(4108): FATAL EXCEPTION: main
02-06 11:31:54.250: E/AndroidRuntime(4108): java.lang.NullPointerException
02-06 11:31:54.250: E/AndroidRuntime(4108): at com.example.sensorsmart.MainActivity.onSensorChanged(MainActivity.java:196)
02-06 11:31:54.250: E/AndroidRuntime(4108): at android.hardware.SystemSensorManager$ListenerDelegate$1.handleMessage(SystemSensorManager.java:204)
02-06 11:31:54.250: E/AndroidRuntime(4108): at android.os.Handler.dispatchMessage(Handler.java:99)
02-06 11:31:54.250: E/AndroidRuntime(4108): at android.os.Looper.loop(Looper.java:137)
02-06 11:31:54.250: E/AndroidRuntime(4108): at android.app.ActivityThread.main(ActivityThread.java:4759)
02-06 11:31:54.250: E/AndroidRuntime(4108): at java.lang.reflect.Method.invokeNative(Native Method)
02-06 11:31:54.250: E/AndroidRuntime(4108): at java.lang.reflect.Method.invoke(Method.java:511)
02-06 11:31:54.250: E/AndroidRuntime(4108): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
02-06 11:31:54.250: E/AndroidRuntime(4108): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:558)
02-06 11:31:54.250: E/AndroidRuntime(4108): at dalvik.system.NativeStart.main(Native Method)