How to get sensor data sequentially?

Question

I'm working on an application that uses sensors. I would get the opportunity to display sensor data in the console in the order given. First, I get and view the data from the accelerometer, next magnetometer data. Currently, data are displayed at random. Once the accelerometer, once the magnetometer. Sometimes they appear twice.

Here is my code:

public class StartFragment extends Fragment implements SensorEventListener {

private SensorManager sensorManager;
private Sensor accelerometer;
private Sensor magnetic;
private static final int PERIOD = 10000;
private Handler handler;
boolean flag = false;

private final Runnable processSensors = new Runnable() {
    @Override
    public void run() {
        sensorManager.registerListener(StartFragment.this, accelerometer, SensorManager.SENSOR_DELAY_UI);
        sensorManager.registerListener(StartFragment.this, magnetic, SensorManager.SENSOR_DELAY_UI);
        flag = true;

        handler.postDelayed(this, PERIOD);
    }
};

public StartFragment(){}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    return inflater.inflate(R.layout.fragment_start, container, false);
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    handler = new Handler();
    sensorManager = (SensorManager) getActivity().getSystemService(Context.SENSOR_SERVICE);
    accelerometer = sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
    magnetic = sensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);
}

@Override
public void onResume() {
    super.onResume();
    handler.post(processSensors);
}

@Override
public void onPause() {
    super.onPause();
    handler.removeCallbacks(processSensors);
    sensorManager.unregisterListener(this, accelerometer);
    sensorManager.unregisterListener(this, magnetic);
}

@Override
public void onSensorChanged(SensorEvent sensorEvent) {
    float[] value = sensorEvent.values;
    if (flag) {

        Log.d("Current sensor: ", sensorEvent.sensor.getName() + " x: " + Float.toString(value[0]));
        Log.d("Current sensor: ", sensorEvent.sensor.getName() + " y: " + Float.toString(value[1]));
        Log.d("Current sensor: ", sensorEvent.sensor.getName() + " z: " + Float.toString(value[2]));

        flag = false;
    }
}

@Override
public void onAccuracyChanged(Sensor sensor, int i) {}

Answer 1

I believe that there's something wrong in your approach. Sensors work asynchronously, and they answer when they can answer. The software role is to get the answers and use them, when they come.

The solution in your case, imho, is, either to start and initialize any sensor after you got the previous sensor's value, or, much better, just work asynchronously and keep your visualization independent (that is by the way one of the basics of mvp programming)