Android: canvas.drawBitmap with Orientation(MagnetField)Sensor

Question

hallo, i am developing Android app with orientation sensor. now i got problem. What i want to do is, change scale and position of bitmap which read from sd card. The scale and position depend on value from orientation sensor. i use canvas.drawBitmap(), then it cause problem. the app is just shut down. other drawXXX()methods have no problem..any suggestion?

public class AnMagImgtestActivity extends Activity implements SensorEventListener
private SensorManager sensorManager;
private MySurfaceView view;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
sensorManager = (SensorManager)getSystemService(SENSOR_SERVICE);
view = new MySurfaceView(this);
}

 @Override
 protected void onResume() {
 super.onResume();

 List<Sensor> sensors = sensorManager.getSensorList(Sensor.TYPE_ORIENTATION);
 if (sensors.size() > 0) {
   Sensor sensor = sensors.get(0);
   sensorManager.registerListener(this, sensor, SensorManager.SENSOR_DELAY_GAME);
   }
 }

 @Override
 protected void onPause() {
 super.onPause();
 sensorManager.unregisterListener(this);
 }

 @Override
 public void onSensorChanged(SensorEvent event) {
 view.onValueChanged(event.values);
 }

 class MySurfaceView extends SurfaceView implements SurfaceHolder.Callback{
 public MySurfaceView(Context context) {
 super(context);
 getHolder().addCallback(this);    
 }

 @Override
 public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
 onValueChanged(new float[3]);
 }

 @Override
 public void surfaceCreated(SurfaceHolder holder) {
}

@Override
public void surfaceDestroyed(SurfaceHolder holder) {
}

void onValueChanged(float[] values) {
Canvas canvas = getHolder().lockCanvas();
String imgfn = "/sdcard/some.jpg";

File mf = new File(imgfn);
Bitmap bitmap0 = BitmapFactory.decodeFile(mf.getPath());

if (canvas != null) {
 Paint paint = new Paint();
 paint.setAntiAlias(true);
 paint.setColor(Color.GREEN);
 paint.setTextSize(12);

 canvas.drawColor(Color.BLACK);

 paint.setAlpha(200);

 for (int i = 0; i < values.length; i++) {
  canvas.drawText("values[" + i + "]: " + values[i], 0, paint.getTextSize() * (i + 1), paint);
}


paint.setColor(Color.WHITE);
paint.setTextSize(100+values[2]);
paint.setAlpha( (int) (255-values[2]));

canvas.drawText("something", values[0]*1+20, paint.getTextSize() * 1+values[2]-80, paint);
///here is the problem..
canvas.drawBitmap(bitmap0, values[0],values[1], paint);

getHolder().unlockCanvasAndPost(canvas);
   }
  }
 }
}