我有以下函數用于監聽加速度計和磁力計值：  // Storage for Sensor readings  public float[] mGravity = new float[3];  public float[] mGeomagnetic = new float[3];  public void registerSensors(Context context) {        // First, get an instance of the SensorManager        SensorManager sMan = (SensorManager) context.getSystemService(Context.SENSOR_SERVICE);        // Second, get the sensor you're interested in        Sensor magnetField = sMan.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);        // Get a reference to the accelerometer        Sensor accelerometer = sMan.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);        // Third, implement a SensorEventListener class        SensorEventListener magnetListener = new SensorEventListener() {            public void onAccuracyChanged(Sensor sensor, int accuracy) {                // do things if you're interested in accuracy changes            }            public void onSensorChanged(SensorEvent event) {                mGravity = new float[3];                //Log.i("LocationUpdater", "magnetometer updated");                System.arraycopy(event.values, 0, mGravity, 0, 3);                //Log.i("LocationUpdater", Float.toString(mGravity[0]));            }        };        SensorEventListener accelListener = new SensorEventListener() {            public void onAccuracyChanged(Sensor sensor, int accuracy) {                // do things if you're interested in accuracy changes            }            public void onSensorChanged(SensorEvent event) {                mGeomagnetic = new float[3];                //Log.i("LocationUpdater", "accelerometer updated");                System.arraycopy(event.values, 0, mGeomagnetic, 0, 3);            }        };但是，從傳感器讀取的值不會寫入數組，所有值都會保留0。這是為什么？