[android help] Android: Detect if camera is parallel to surface before taking a picture

Requirement:

I need to detect if the camera is parallel to surface before I allow user to click picture using camera

I have already read Android developers Sensor manager notes and tried the sample code

I already have a custom camera for my app

edit1: below code never fires

public void onSensorChanged(SensorEvent event) {
 }

edit2 my code

    public class OrientationDemo extends Activity implements
SensorEventListener {
        TextView mOrientationData;
        private SensorManager mSensMan;
        private float mAzimuth;
        private float[] mGravs = new float[3];
        private float[] mGeoMags = new float[3];
        private float[] mOrientation = new float[3];
        private float[] mRotationM = new float[9];               // Use [16]
to co-operate with android.opengl.Matrix
        private float[] mRemapedRotationM = new float[9];
        private boolean mFailed;


    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

//      I'd like to actually see something so let's have a view:
        mOrientationData = new TextView(this);
        setContentView(mOrientationData, new
LayoutParams(LayoutParams.FILL_PARENT,LayoutParams.FILL_PARENT));

//      Initiate the Sensor Manager and register this as Listener for
the required sensor types:
//        TODO: Find how to get a SensorManager outside an Activity, to
implement as a utility class.
                mSensMan = (SensorManager) getSystemService(SENSOR_SERVICE);
                mSensMan.registerListener(this,
                                mSensMan.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD), //
Anonymous Sensors- no further use for them.
                                SensorManager.SENSOR_DELAY_UI);
                mSensMan.registerListener(this,
mSensMan.getDefaultSensor(Sensor.TYPE_ACCELEROMETER),
                                SensorManager.SENSOR_DELAY_UI);
    }

        @Override
        public void onAccuracyChanged(Sensor sensor, int accuracy) {
                // Do nothing
        }

        @Override
        public void onSensorChanged(SensorEvent event) {
                switch (event.sensor.getType()) {
                case Sensor.TYPE_ACCELEROMETER:
                        /*
                         * NOTE: The data must be copied off the event.values
                         * as the system is reusing that array in all SensorEvents.
                         * Simply assigning:
                         * mGravs = event.values won't work.
                         *
                         * I use a member array in an attempt to reduce garbage production.
                         */
                        System.arraycopy(event.values, 0, mGravs, 0, 3);
                        break;
                case Sensor.TYPE_MAGNETIC_FIELD:
                        // Here let's try another way:
                        for (int i=0;i<3;i++) mGeoMags[i] = event.values[i];
                                break;
                        default:
                                return;
                }

                if (SensorManager.getRotationMatrix(mRotationM, null, mGravs,
mGeoMags)){
//                        Rotate to the camera's line of view (Y axis along the camera's
axis)
//                        TODO: Find how to use android.opengl.Matrix to rotate to an
arbitrary coordinate system.
                        SensorManager.remapCoordinateSystem(mRotationM,
SensorManager.AXIS_X,
                                        SensorManager.AXIS_Z, mRemapedRotationM);
                        SensorManager.getOrientation(mRemapedRotationM, mOrientation);
                        onSuccess();
                }
                else onFailure();
        }

        void onSuccess(){
                if (mFailed) mFailed = false;
//                Convert the azimuth to degrees in 0.5 degree resolution.
                mAzimuth = (float) Math.round((Math.toDegrees(mOrientation[0])) *2)/
2;
//                Adjust the range: 0 < range <= 360 (from: -180 < range <= 180).
                mAzimuth = (mAzimuth+360)%360; // alternative: mAzimuth =
mAzimuth>=0 ? mAzimuth : mAzimuth+360;
                mOrientationData.setText("Azimuth= " + mAzimuth);
        }

        void onFailure() {
                if (!mFailed) {
                        mFailed = true;
                        mOrientationData.setText("Failed to retrive rotation Matrix");
                }
        }
}

I need sample app that can give me rotation matrix for my device

Thanks in advance!!!

.

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