Android Sensor
This tutorial describes how to use the Androids Sensor manager. The tutorial is based on Eclipse 3.6, Java 1.6 and Android 2.3.3 (Gingerbread).
Table of Contents
Sensors Android 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 Sensorclass 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 take as parameters the sensor type and the deplay defined as constants on SensorManager.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 = System.currentTimeMillis();
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);
}
}
Create a new Android project called de.vogella.android.sensor.compass with an activity calledMainActivity.
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 directio
// 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);
}
}
}
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