Getting pitch and roll value

Question

I am doing a project which is detecting the direction of moving by using accelerometer However, the 3 axis of accelerometer will not always follow the world xyz plane as we tilt or rotate our phone. I was trying to fix it by getting the pitch and roll from the phone and convert the axis of the phone to the world xyz axis. But now my pitch and roll always get 0. Can anyone help me ? or is there any other way to solve my problem? Thanks for the help!

package com.example.suntracking;

import android.app.Activity;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;

public class AxisCheck extends Activity implements SensorEventListener{

    Sensor accelerometer,magnetometer;
    float[] lastAccelerometer = new float[3];
    float[] lastMagnetometer = new float[3];
    boolean lastAccelerometerSet = false;
    boolean lastMagnetometerSet = false;

    SensorManager sm;
    float pval,rval;
    float[] mR = new float[9];
    float[] mhold= new float[3];

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        initialize();
        accelerometer = sm.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
        magnetometer = sm.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);
        finish();
    }


    @Override
    protected void onResume() {
        // TODO Auto-generated method stub
        super.onResume();
        sm.registerListener(this, accelerometer, SensorManager.SENSOR_DELAY_NORMAL);
        sm.registerListener(this, magnetometer, SensorManager.SENSOR_DELAY_NORMAL);
    }

    protected void onPause() {
        super.onPause();
        sm.unregisterListener(this);
    }
    @Override
    public void onAccuracyChanged(Sensor arg0, int arg1) {
        // TODO Auto-generated method stub
    }


    private void initialize() {
        // TODO Auto-generated method stub
        sm =(SensorManager)getSystemService(SENSOR_SERVICE);
    }


    @Override
    public void onSensorChanged(SensorEvent event) {
        // TODO Auto-generated method stub
        if (event.sensor == accelerometer) {
            System.arraycopy(event.values, 0, lastAccelerometer, 0, event.values.length);
            lastAccelerometerSet = true;
        } else if (event.sensor == magnetometer) {
            System.arraycopy(event.values, 0, lastMagnetometer, 0, event.values.length);
            lastMagnetometerSet = true;
        }
        if (lastAccelerometerSet && lastMagnetometerSet) {
        SensorManager.getRotationMatrix(mR, null, lastAccelerometer, lastMagnetometer);
        SensorManager.getOrientation(mR,mhold);
        pval = Math.round(mhold[1]);
        rval = Math.round(mhold[2]);
        savePreferences();
        }
    }


    private void savePreferences() {
        // TODO Auto-generated method stub
        SharedPreferences savedata = getSharedPreferences("savealldata",0);
        Editor editor=savedata.edit();
        editor.putFloat("pval", pval);
        editor.putFloat("rval", rval);
        editor.commit();
    }


}