GravityActivity.java

package com.google.mcommerce.sample.android.chapter08.sensor;

import android.app.Activity;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.widget.TextView;

import com.google.mcommerce.sample.android.R;

public class GravityActivity extends Activity implements SensorEventListener {
	private SensorManager mgr;
	private Sensor accelerometer;
	private TextView text;
	private float[] gravity = new float[3];
	private float[] motion = new float[3];
	private double ratio;
	private double mAngle;
	private int counter = 0;

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.c08_sensor_gravity);

		mgr = (SensorManager) this.getSystemService(SENSOR_SERVICE);

		accelerometer = mgr.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);

		text = (TextView) findViewById(R.id.text);
	}

	@Override
	protected void onResume() {
		mgr.registerListener(this, accelerometer, SensorManager.SENSOR_DELAY_UI);
		super.onResume();
	}

	@Override
	protected void onPause() {
		mgr.unregisterListener(this, accelerometer);
		super.onPause();
	}

	public void onAccuracyChanged(Sensor sensor, int accuracy) {
		// ignore
	}

	public void onSensorChanged(SensorEvent event) {
		// Use a low-pass filter to get gravity. Motion is what's left over
		for (int i = 0; i < 3; i++) {
			gravity[i] = (float) (0.1 * event.values[i] + 0.9 * gravity[i]);
			motion[i] = event.values[i] - gravity[i];
		}

		// ratio is gravity on the Y axis compared to full gravity
		// should be no more than 1, no less than -1
		ratio = gravity[1] / SensorManager.GRAVITY_EARTH;
		if (ratio > 1.0)
			ratio = 1.0;
		if (ratio < -1.0)
			ratio = -1.0;

		// convert ratio to radians to degrees, make negative if facing up
		mAngle = Math.toDegrees(Math.acos(ratio));
		if (gravity[2] < 0) {
			mAngle = -mAngle;
		}

		// Display every 10th value
		if (counter++ % 10 == 0) {
			String msg = String
					.format("Raw values\nX: %8.4f\nY: %8.4f\nZ: %8.4f\n"
							+ "Gravity\nX: %8.4f\nY: %8.4f\nZ: %8.4f\n"
							+ "Motion\nX: %8.4f\nY: %8.4f\nZ: %8.4f\nAngle: %8.1f",
							event.values[0], event.values[1], event.values[2],
							gravity[0], gravity[1], gravity[2], motion[0],
							motion[1], motion[2], mAngle);
			text.setText(msg);
			text.invalidate();
			counter = 1;
		}
	}
}