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Android Sensor - Tutorial

Lars Vogel

Version 0.4

07.03.2012

Android Sensor

This tutorial describes how to use the Android Sensor manager. The tutorial is based on Eclipse 3.6, Java 1.6 and Android 2.3.3 (Gingerbread).


Table of Contents

1. Android Sensors
1.1. SensorManager
1.2. Sensor listener
2. Tutorial: Accelerometer
3. Tutorial: Building a compass
4. About this website
4.1. Donate to support free tutorials
4.2. Questions and discussion
4.3. License for this tutorial and its code
5. Links and Literature
5.1. Source Code
5.2. Android Resources
5.3. vogella Resources

1. Android Sensors

1.1. SensorManager

Android Sensors supports several sensors via the SensorManager, for example the accelerometer. Unfortunately, you cannot test the accelerometer on the Android emulator.

You can access a SensorManager via getSystemService(SENSOR_SERVICE). The Sensor class defines several constants for accessing the different sensors.

  • Sensor.TYPE_GYROSCOPE

  • Sensor.TYPE_MAGNETIC_FIELD

  • Sensor.TYPE_ORIENTATION

  • Sensor.TYPE_ACCELEROMETER

You can access the sensor via the sensorManager.getDefaultSensor() method, which takes the sensor type and the delay defined as constants on SensorManager as parameters.

1.2. Sensor listener

Once you acquired a sensor, you can register a SensorEventListener object on it. This listener will get informed, if the sensor data changes.

To avoid the unnecessary usage of battery power, you can register your listener in the onResume() method and de-register it in the onPause() method.

2. Tutorial: Accelerometer

We will build an application which will change its background color if it is shuffled. Create a new Android project called de.vogella.android.sensor with an activity called SensorTestActivity.

Change your layout file to the following code.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="Shake to get a toast and to switch color" />

</LinearLayout> 

Change your activity class to the following code.

package de.vogella.android.sensor;

import android.app.Activity;
import android.graphics.Color;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.view.View;
import android.view.Window;
import android.view.WindowManager;
import android.widget.Toast;

public class SensorTestActivity extends Activity implements SensorEventListener {
  private SensorManager sensorManager;
  private boolean color = false;
  private View view;
  private long lastUpdate;

  
/** Called when the activity is first created. */
@Override public void onCreate(Bundle savedInstanceState) { requestWindowFeature(Window.FEATURE_NO_TITLE); getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN); super.onCreate(savedInstanceState); setContentView(R.layout.main); view = findViewById(R.id.textView); view.setBackgroundColor(Color.GREEN); sensorManager = (SensorManager) getSystemService(SENSOR_SERVICE); lastUpdate = System.currentTimeMillis(); } @Override public void onSensorChanged(SensorEvent event) { if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER) { getAccelerometer(event); } } private void getAccelerometer(SensorEvent event) { float[] values = event.values; // Movement float x = values[0]; float y = values[1]; float z = values[2]; float accelationSquareRoot = (x * x + y * y + z * z) / (SensorManager.GRAVITY_EARTH * SensorManager.GRAVITY_EARTH); long actualTime = event.timestamp; if (accelationSquareRoot >= 2) // { if (actualTime - lastUpdate < 200) { return; } lastUpdate = actualTime; Toast.makeText(this, "Device was shuffed", Toast.LENGTH_SHORT) .show(); if (color) { view.setBackgroundColor(Color.GREEN); } else { view.setBackgroundColor(Color.RED); } color = !color; } } @Override public void onAccuracyChanged(Sensor sensor, int accuracy) { } @Override protected void onResume() { super.onResume(); // register this class as a listener for the orientation and // accelerometer sensors sensorManager.registerListener(this, sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER), SensorManager.SENSOR_DELAY_NORMAL); } @Override protected void onPause() { // unregister listener super.onPause(); sensorManager.unregisterListener(this); } }

3. Tutorial: Building a compass

Create a new Android project called de.vogella.android.sensor.compass with an activity called MainActivity.

Create the following custom View class.

package de.vogella.android.sensor.compass;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.View;

public class MyCompassView extends View {

  private Paint paint;
  private float position = 0;

  public MyCompassView(Context context) {
    super(context);
    init();
  }

  private void init() {
    paint = new Paint();
    paint.setAntiAlias(true);
    paint.setStrokeWidth(2);
    paint.setTextSize(25);
    paint.setStyle(Paint.Style.STROKE);
    paint.setColor(Color.WHITE);
  }

  @Override
  protected void onDraw(Canvas canvas) {
    int xPoint = getMeasuredWidth() / 2;
    int yPoint = getMeasuredHeight() / 2;

    float radius = (float) (Math.max(xPoint, yPoint) * 0.6);
    canvas.drawCircle(xPoint, yPoint, radius, paint);
    canvas.drawRect(0, 0, getMeasuredWidth(), getMeasuredHeight(), paint);

    // 3.143 is a good approximation for the circle
    canvas.drawLine(xPoint,
        yPoint,
        (float) (xPoint + radius
            * Math.sin((double) (-position) / 180 * 3.143)),
        (float) (yPoint - radius
            * Math.cos((double) (-position) / 180 * 3.143)), paint);

    canvas.drawText(String.valueOf(position), xPoint, yPoint, paint);
  }

  public void updateData(float position) {
    this.position = position;
    invalidate();
  }

} 

Change the coding of your activity.

package de.vogella.android.sensor.compass;

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.Toast;

public class MainActivity extends Activity {

  private static SensorManager sensorService;
  private MyCompassView compassView;
  private Sensor sensor;

  
/** Called when the activity is first created. */
@Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); compassView = new MyCompassView(this); setContentView(compassView); sensorService = (SensorManager) getSystemService(Context.SENSOR_SERVICE); sensor = sensorService.getDefaultSensor(Sensor.TYPE_ORIENTATION); if (sensor != null) { sensorService.registerListener(mySensorEventListener, sensor, SensorManager.SENSOR_DELAY_NORMAL); Log.i("Compass MainActivity", "Registerered for ORIENTATION Sensor"); } else { Log.e("Compass MainActivity", "Registerered for ORIENTATION Sensor"); Toast.makeText(this, "ORIENTATION Sensor not found", Toast.LENGTH_LONG).show(); finish(); } } private SensorEventListener mySensorEventListener = new SensorEventListener() { @Override public void onAccuracyChanged(Sensor sensor, int accuracy) { } @Override public void onSensorChanged(SensorEvent event) { // angle between the magnetic north direction // 0=North, 90=East, 180=South, 270=West float azimuth = event.values[0]; compassView.updateData(azimuth); } }; @Override protected void onDestroy() { super.onDestroy(); if (sensor != null) { sensorService.unregisterListener(mySensorEventListener); } } }

4. About this website

4.1. Donate to support free tutorials

Please consider a contribution Support free tutorials if this article helped you. It will help to maintain our content and our Open Source activities.

4.2. Questions and discussion

Writing and updating these tutorials is a lot of work. If this free community service was helpful, you can support the cause by giving a tip as well as reporting typos and factual errors.

If you find errors in this tutorial, please notify me (see the top of the page). Please note that due to the high volume of feedback I receive, I cannot answer questions to your implementation. Ensure you have read the vogella FAQ as I don't respond to questions already answered there.

4.3. License for this tutorial and its code

This tutorial is Open Content under the CC BY-NC-SA 3.0 DE license. Source code in this tutorial is distributed under the Eclipse Public License. See the vogella License page for details on the terms of reuse.

5. Links and Literature

5.1. Source Code

Source Code of Examples

5.3. vogella Resources

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