Android – Accelerometer Basic Usage

Posted by cristi on Mar 19, 2010 in Snippets | 2 comments

Do you want to access the accelerometer (or some other sensor) in your device and use its data in your application? Here is a way of doing that. Let’s see the basic form of an application that monitors changes to the accelerometer sensor:

import android.app.Activity;
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;

public class TestMain extends Activity implements SensorEventListener{
    private TextView mainText; // here we display accelerometer info
    private SensorManager mySensorManager; // used to acquire sensor access
    private Sensor accSensor; // accelerometer sensor object
    // ...

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        mainText = (TextView)findViewById(R.id.main_text);

        // Set SensorManager and acquire a reference to accelerometer sensor
        mySensorManager = (SensorManager)getSystemService(
                                        Context.SENSOR_SERVICE);
        accSensor = mySensorManager.getSensorList(
                                        Sensor.TYPE_ACCELEROMETER).get(0);
        // it may be a good idea to first check the returned Sensor list
        // size to be sure we actually did get an accelerometer reference
        // ...
    }

    // register current SensorEventListener
    @Override
    protected void onResume()
    {
        super.onResume();
        mySensorManager.registerListener(this, accSensor,
                            SensorManager.SENSOR_DELAY_NORMAL);
    }

    // unregister current SensorEventListener
    @Override
    protected void onStop()
    {
        mySensorManager.unregisterListener(this);
        super.onStop();
    }

    // receives accuracy changes form sensor
    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {
        Log.d("TestingArea","onAccuracyChanged: " + sensor +
              " has accuracy: " + accuracy);
    }

    // receives sensor changes
    @Override
    public void onSensorChanged(SensorEvent event) {
        if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER)
            mainText.setText("acc x = " + event.values[0] +
                            "\nacc y = " + event.values[1] +
                            "\nacc z = " + event.values[2]);
    }

    // ...
}

• We need a SensorManager object to access sensors (we instantiated it in the onCreate() method by using Context method getSystemService(Context.SENSOR_SERVICE)).

• We use getSensorList() method on the SensorManager object to acquire the sensors we want – we use as parameter  TYPE_ACCELEROMETER to access accelerometer sensor (for others take a look at Sensor documentation).

• We need a class implementing SensorEventListener to be able to receive accelerometer changes – we use the main Activity as the Listener in this example, other options may be more appropriate in other situations. Try not to use SensorListener interface as it is deprecated!

• The SensorEventListener must implement two methods – onSensorChanged() and onAccuracyChanged() – and that’s where we’ll receive the accelerometer values.

• We need to register the Listener with the SensorManager to start receiving accelerometer info. A good place to do that is onResume() method as the Activity could be restarted by orientation change or other events . Also unregistering the Listener when it’s not needed is recommended – a good place to do that is onStop() method.

• That’s all, we now receive SensorEvents and we can easily get the three axis accelerometer values by using event.values[x] in our onSensorChanged() method.

A full tutorial with in depth examples of Sensors will follow hopefully soon. Stay tuned.

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