How to measure time in Android?

Question

I am developing a Human Activity Recognition Android application and I have to measure both time being sedentary (static) and time spent active. At first, I thought to store a long variable in the sharedPreferences and increment it every 5 seconds (I am classifying the user activity every 5 seconds) by 5000 (5 seconds in milliseconds).

However, when I start my service (I am using a background service to do the classification and store it in the SharedPreferences) and check at a later point - say after 2 hours, the time I have in the sharedPreferences and the actual time that has passed differs significantly. For example, I will start my service at 12pm and check at 2pm and the value in the shared preferences will be something like 40 minutes (when converted from milliseconds - value/1000/60 minutes).

P.S.: My service looks like that:

public class MyService extends Service implements SensorEventListener {
public static final String COUNTER_KEY = "counterKey3";
public int counter = 0;
private static final long WINDOW_LENGTH = 5000;
private long windowBegTime = -1;
private SensorManager mSensorManager;
private Sensor accSensor;
private ArrayList<Double> xValues = new ArrayList<>();
private ArrayList<Double> yValues = new ArrayList<>();
private ArrayList<Double> zValues = new ArrayList<>();

private SharedPreferences mSharedPreferences;

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
    super.onStartCommand(intent, flags, startId);
    mSensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
    accSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
    mSensorManager.registerListener(this, accSensor, SensorManager.SENSOR_DELAY_GAME);
    return START_STICKY;
}

@Override
public void onCreate() {
    super.onCreate();
    mSharedPreferences = getSharedPreferences(getPackageName(), MODE_PRIVATE);
    counter = mSharedPreferences.getInt(COUNTER_KEY, 0);

}


@Override
public void onSensorChanged(SensorEvent sensorEvent) {
    xValues.add((double) sensorEvent.values[0]);
    yValues.add((double) sensorEvent.values[1]);
    zValues.add((double) sensorEvent.values[2]);

    if (SystemClock.elapsedRealtime() - windowBegTime > WINDOW_LENGTH) {
        if (windowBegTime > 0) {
            mSharedPreferences.edit().putInt(COUNTER_KEY, mSharedPreferences.getInt(COUNTER_KEY, 0) + 5).apply();
            Log.i("MyService", "WindowTimeIssue! " + mSharedPreferences.getInt(COUNTER_KEY, 0));
                // DETECT ACTIVITY - store it in a db

        }

        windowBegTime = SystemClock.elapsedRealtime();
    }
}


}

Answer 1

You need to make your service a foreground service. Background services are killed by OS when resources are needed.

Intent intent = new Intent(this, MyActivityApp.class);
PendingIntent pi = PendingIntent.getActivity(this, 0, intent,   PendingIntent.FLAG_UPDATE_CURRENT);    

    NotificationCompat.Builder builder = new NotificationCompat.Builder(this);

    builder.setSmallIcon(Resource.Drawable.my_icon);
    builder.setTicker("My Activity App");
    builder.setContentIntent(pi);
    builder.setOngoing(true);
    builder.setOnlyAlertOnce(true);

    Notification notification = builder.build();   
    startForeground(SERVICE_NOTIFICATION_ID, notification);

Also, you should look into Activity Recognition API (https://developers.google.com/android/reference/com/google/android/gms/location/ActivityRecognitionApi)