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environment

- Leakage

Sensor Leak

11 December 2020

Olivier Le Goaer

android

java

Most Android-powered devices have built-in sensors that measure motion, orientation, and various environmental conditions. In addition to these are the image sensor (a.k.a Camera) and the geopositioning sensor (a.k.a GPS). The common point of all these sensors is that they are expensive while in use. Their common bug is to let the sensor unnecessarily process data when the app enters an idle state, typically when paused or stopped. Consequently, calls must be carefully pairwised: SensorManager#registerListener()/unregisterListener() for regular sensors, Camera#open()/Camera#release() for the camera and LocationManager#requestLocationUpdates()/removeUpdates() for the GPS. Failing to do so can drain the battery in just a few hours.

Noncompliant Code

sensorManager = (SensorManager) getActivity().getSystemService(Context.SENSOR_SERVICE);
    accelerometer = sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
    sensorManager.registerListener(this, accelerometer, 20000);
...

Compliant Solution

sensorManager = (SensorManager) getActivity().getSystemService(Context.SENSOR_SERVICE);
    accelerometer = sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
    sensorManager.registerListener(this, accelerometer, 20000);
...
sensorManager.unregisterListener(this);