A utility class to help get current device orientation, you will need it if you decided to fix the activity's orientation in the manifest :)

DeviceOrientation

import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.media.ExifInterface;

/**
 * Created by abdelhady on 9/23/14.
 *
 * to use this class do the following 3 steps in your activity:
 *
 * define 3 sensors as member variables
        Sensor accelerometer;
        Sensor magnetometer;
        Sensor vectorSensor;
        DeviceOrientation deviceOrientation;
 *
 * add this to the activity's onCreate
        mSensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
        accelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
        magnetometer = mSensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);
        deviceOrientation = new DeviceOrientation();
 *
 * add this to onResume
        mSensorManager.registerListener(deviceOrientation.getEventListener(), accelerometer, SensorManager.SENSOR_DELAY_UI);
        mSensorManager.registerListener(deviceOrientation.getEventListener(), magnetometer, SensorManager.SENSOR_DELAY_UI);
 *
 * add this to onPause
        mSensorManager.unregisterListener(deviceOrientation.getEventListener());
 *
 *
 * then, you can simply call * deviceOrientation.getOrientation() * wherever you want
 *
 *
 * another alternative to this class's approach:
 * http://stackoverflow.com/questions/11175599/how-to-measure-the-tilt-of-the-phone-in-xy-plane-using-accelerometer-in-android/15149421#15149421
 *
 */
public class DeviceOrientation {
    private final int ORIENTATION_PORTRAIT = ExifInterface.ORIENTATION_ROTATE_90; // 6
    private final int ORIENTATION_LANDSCAPE_REVERSE = ExifInterface.ORIENTATION_ROTATE_180; // 3
    private final int ORIENTATION_LANDSCAPE = ExifInterface.ORIENTATION_NORMAL; // 1
    private final int ORIENTATION_PORTRAIT_REVERSE = ExifInterface.ORIENTATION_ROTATE_270; // 8

    int smoothness = 1;
    private float averagePitch = 0;
    private float averageRoll = 0;
    private int orientation = ORIENTATION_PORTRAIT;

    private float[] pitches;
    private float[] rolls;

    public DeviceOrientation() {
        pitches = new float[smoothness];
        rolls = new float[smoothness];
    }

    public SensorEventListener getEventListener() {
        return sensorEventListener;
    }

    public int getOrientation() {
        return orientation;
    }

    SensorEventListener sensorEventListener = new SensorEventListener() {
        float[] mGravity;
        float[] mGeomagnetic;

        @Override
        public void onSensorChanged(SensorEvent event) {
            if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER)
                mGravity = event.values;
            if (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD)
                mGeomagnetic = event.values;
            if (mGravity != null && mGeomagnetic != null) {
                float R[] = new float[9];
                float I[] = new float[9];
                boolean success = SensorManager.getRotationMatrix(R, I, mGravity, mGeomagnetic);
                if (success) {
                    float orientationData[] = new float[3];
                    SensorManager.getOrientation(R, orientationData);
                    averagePitch = addValue(orientationData[1], pitches);
                    averageRoll = addValue(orientationData[2], rolls);
                    orientation = calculateOrientation();
                }
            }
        }

        @Override
        public void onAccuracyChanged(Sensor sensor, int accuracy) {
            // TODO Auto-generated method stub

        }
    };

    private float addValue(float value, float[] values) {
        value = (float) Math.round((Math.toDegrees(value)));
        float average = 0;
        for (int i = 1; i < smoothness; i++) {
            values[i - 1] = values[i];
            average += values[i];
        }
        values[smoothness - 1] = value;
        average = (average + value) / smoothness;
        return average;
    }

    private int calculateOrientation() {
        // finding local orientation dip
        if (((orientation == ORIENTATION_PORTRAIT || orientation == ORIENTATION_PORTRAIT_REVERSE)
                && (averageRoll > -30 && averageRoll < 30))) {
            if (averagePitch > 0)
                return ORIENTATION_PORTRAIT_REVERSE;
            else
                return ORIENTATION_PORTRAIT;
        } else {
            // divides between all orientations
            if (Math.abs(averagePitch) >= 30) {
                if (averagePitch > 0)
                    return ORIENTATION_PORTRAIT_REVERSE;
                else
                    return ORIENTATION_PORTRAIT;
            } else {
                if (averageRoll > 0) {
                    return ORIENTATION_LANDSCAPE_REVERSE;
                } else {
                    return ORIENTATION_LANDSCAPE;
                }
            }
        }
    }
}

Super working.. 👍

I thought it would be nice to share the logic behind the calculation,
when in portrait (my apps default orientation), users could roll the device a little right or left, but if they rolled it too much (more than 30 degrees) then we need to recalculate the new situation.
See this image for a better understanding of roll and pitch

The for loop inside addvalue is never executing. What is its purpose?

@anuj-github, I don't fully remember now, but I guess it was basically for getting smoother results, but then I figured that using the smothering constant of 1 is already enough, but probably I left the smothering logic anyways for anyone who might wanna try a different value