Sensors Overview

Sensors Overview

The Android platform supports three broad categories of sensors:

a> Motion sensors

These sensors measure acceleration forces and rotational forces along three axes. This category includes accelerometers, gravity sensors, gyroscopes, and rotation vector sensors.

b> Environmental sensors

These sensors measure various environmental parameters, such as ambient air temperature and pressure, illumination, and humidity. This category includes barometers, photometers, and thermometers.

c> Position sensors

These sensors measure the physical position of a device. This category includes orientation sensors and magnetometers.

We can use the sensor framework to do the following:

a> Determine which sensors are available on a device.

b> Determine an individual sensor's capabilities

c> Acquire raw sensor data and define the minimum rate at which you acquire sensor data.

d> Register and unregister sensor event listeners that monitor sensor changes.

Introduction to Sensors

Most handset devices and tablets have an accelerometer and a magnetometer, but fewer devices have barometers or thermometers.

Sensor Framework

In a typical application we use these sensor-related APIs to perform two basic tasks: a> Identifying sensors and sensor capabilities, and b> Monitor sensor events.

Identifying sensors ans Sensor Capabilities

To identify the sensors that are on a device you first need to get a reference to the sensor service. To do this, you create an instance of the SensorManager class by calling the getSystemService() method and passing in the SENSOR_SERVICE argument. Next, you can get a listing of every sensor on a device by calling the getSensorList() method and using the TYPE_ALL constant.

	private List<Sensor> getAllSensorsOnDevice() {
		SensorManager manager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
		return manager.getSensorList(Sensor.TYPE_ALL);
	}

You can also determine whether a specific type of sensor exists on a device by using the getDefaultSensor() method and passing in the type constant for a specific sensor.

	private boolean isAccelerometerSensorAvailable(){
		SensorManager manager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
		return manager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER) == null;
	}

Monitoring Sensor Events

To monitor raw sensor data you need to implement two callback methods that are exposed through the SensorEventListener interface: onAccuracyChanged() and onSensorChanged().

a> A sensor's accuracy changes:

In this case the system invokes the onAccuracyChanged() method, providing you with a reference to the sensor object that changed and the new accuracy of the sensor. Accuracy is represented by one of four status constants: SENSOR_STATUS_ACCURACY_LOW, SENSOR_STATUS_ACCURACY_MEDIUM, SENSOR_STATUS_ACCURACY_HIGH, SENSOR_STATUS_ACCURACY_UNRELIABLE.

b> A sensor reports a new value:

In this case the system invokes the onSensorChanged() method, providing you with a SensorEvent object.

public class MainActivity extends Activity {

	private SensorManager mSensorManager;
	private Sensor mSensor;
	private SensorEventListener mSensorEventListener;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
		mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
		mSensorEventListener = new SensorEventListener() {

			@Override
			public void onSensorChanged(SensorEvent event) {
				Log.i("tag", "onSensorChanged");
				int value = (int) event.values[0];
				Log.i("tag", "value = " + value);

			}

			@Override
			public void onAccuracyChanged(Sensor sensor, int accuracy) {
				Log.i("tag", "onAccuracyChanged");
			}
		};
	}
	

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

		mSensorManager.registerListener(mSensorEventListener, mSensor,
				SensorManager.SENSOR_DELAY_GAME);
	}

	@Override
	protected void onPause() {
		super.onPause();
		
		mSensorManager.unregisterListener(mSensorEventListener, mSensor);
	}
}