Wednesday, June 29, 2011

Android Service and Broadcast Receiver Tutorial


Lars Vogel

Version 1.3
19.03.2011
Revision History
Revision 0.107.03.2011Lars Vogel
created
Revision 0.2 - 1.308.03.2011 - 19.03.2011Lars Vogel
bug fixed and enhancements
Developing services with Android Gingerbread and Eclipse
This tutorial describes how to create and consume Android services. It is based on Eclipse 3.6, Java 1.6 and Android 2.3 (Gingerbread).

1. Android Services

1.1. Service

A service is a component which runs in the background, without interacting with the user.
The Android platform provides a lot of pre-defined services, usually exposed via a Manager class. In your activity you access services via the method getSystemService().
Own Services must be declared via the "AndroidManifest.xml". They run the main thread of their hosting process. Therefore you should run performance intensive tasks in the background .

1.2. Own Services

You can declare your own service to perform long running operations without user interaction or to supply functionality to other applications. A activity can start a service via the startService() method and stop the service via the stopService() method. If the activity want to interact with the service it can use the bindService() method of the service. This requires an "ServiceConnection" object which allows to connect to the service and which return a IBinder object. This IBinder object can be used by the activity to communicate with the service.
Once a service is started its onCreate() method is called. Afterwards the onStartCommand() is called with the Intent data provided by the activity. startService also allows to provide a flag with determines the lifecycle behavior of the services. START_STICKY is used for services which are explicit started or stopped. Services started with START_NOT_STICKY will end automatically after the onStartCommand() method is done. A service is started within the main thread of the application therefore all long running tasks should be performed in the background .
A Services needs to be declared in the "AndroidManifest.xml" via a <service android:name="yourclasss"> </service> and the implementing class must extend the class "Service" or one of its subclasses.
One common case is that the service and the activity are very closely related. In this case class just case the IBinder to the class the service provides. See Local Service Example for an example.
Another example would be the usage of Remote Messenger Service. In this case activities can send messages to the service and receive messages as well if they register for them.

1.3. Broadcast Receiver

A broadcast receiver is a class which extends "BroadcastReceiver" and which is registered as a receiver in an Android Application via the AndroidManifest.xml (or via code). This class will be able to receive intents via the sendBroadcast() method. "BroadCastReceiver" defines the method "onReceive()". Only during this method your broadcast receiver object will be valid, afterwards the Android system will consider your object as no longer active. Therefore you cannot perform any asynchronous operation.

1.4. Pending Intent

This tutorial will also use a PendingIntent. A PendingIntent is a token that you give to another application (e.g. Notification Manager, Alarm Manager or other 3rd party applications), which allows this other application to use the permissions of your application to execute a predefined piece of code.
To perform a broadcast via a pending intent so get a PendingIntent via PendingIntent.getBroadcast(). To perform an activity via an pending intent you receive the activity via PendingIntent.getActivity().

2. Broadcast Receiver Example

We will define a broadcast receiver which listens to telephone state changes. If the phone receives a phone call then our receiver will be notified and log a message.
Create a new project "de.vogella.android.receiver.phone". We do not need an activity. Create the following "AndroidManifest.xml".

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
 package="de.vogella.android.receiver.phone" android:versionCode="1"
 android:versionName="1.0">
 <application android:icon="@drawable/icon" android:label="@string/app_name">


  <receiver android:name="MyPhoneReceiver">
   <intent-filter>
    <action android:name="android.intent.action.PHONE_STATE"></action>
   </intent-filter>
  </receiver>
 </application>
 <uses-sdk android:minSdkVersion="9" />


 <uses-permission android:name="android.permission.READ_PHONE_STATE"></uses-permission>
</manifest> 
  

Create the following class "MyPhoneReceiver".

package de.vogella.android.receiver.phone;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.telephony.TelephonyManager;
import android.util.Log;

public class MyPhoneReceiver extends BroadcastReceiver {

 @Override
 public void onReceive(Context context, Intent intent) {
  Bundle extras = intent.getExtras();
  if (extras != null) {
   String state = extras.getString(TelephonyManager.EXTRA_STATE);
   Log.w("DEBUG", state);
   if (state.equals(TelephonyManager.EXTRA_STATE_RINGING)) {
    String phoneNumber = extras
      .getString(TelephonyManager.EXTRA_INCOMING_NUMBER);
    Log.w("DEBUG", phoneNumber);
   }
  }
 }
}

  

If you install your application and receive a call, e.g simulated by the DDMS perspective in Eclipse, then your receiver will be called and lot a message to the console.

3. System Services and Broadcast Receiver

In this chapter we will use the AlertManager and VibratorManager. The VibratorManager will be called by the broadcast receiver which will be called by the AlertManager.
Create a new project "de.vogella.android.alarm" with the activity "AlarmActivity". Create the following layout.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:orientation="vertical" android:layout_width="fill_parent"
 android:layout_height="fill_parent">
 <EditText android:layout_height="wrap_content" android:id="@+id/time"
  android:layout_width="wrap_content" android:hint="Number of seconds"
  android:inputType="numberDecimal">></EditText>
 <Button android:text="Start Counter" android:id="@+id/ok"
  android:onClick="startAlert" android:layout_width="wrap_content"
  android:layout_height="wrap_content"></Button>
</LinearLayout>

   

Create the following broadcast receiver class. This class will get the Vibrator service.

package de.vogella.android.alarm;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.os.Vibrator;
import android.widget.Toast;

public class MyBroadcastReceiver extends BroadcastReceiver {
 @Override
 public void onReceive(Context context, Intent intent) {
  Toast.makeText(context, "Don't panik but your time is up!!!!.",
    Toast.LENGTH_LONG).show();
  // Vibrate the mobile phone
  Vibrator vibrator = (Vibrator) context.getSystemService(Context.VIBRATOR_SERVICE);
  vibrator.vibrate(2000);
 }

}

   

Maintain this class as broadcast receiver in "AndroidManifest.xml" and allow the vibrate authorization.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
 package="de.vogella.android.alarm" android:versionCode="1"
 android:versionName="1.0">
 <uses-sdk android:minSdkVersion="9" />

 <application android:icon="@drawable/icon" android:label="@string/app_name">
  <activity android:name=".AlarmActivity" android:label="@string/app_name">
   <intent-filter>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.LAUNCHER" />
   </intent-filter>
  </activity>
  <receiver android:name="MyBroadcastReceiver"></receiver>

 </application>
 <uses-permission android:name="android.permission.VIBRATE"></uses-permission>
 
</manifest>
   

Change the code of your Activity "AlarmActivity" to the following. This activity will create an Intent for the Broadcast receiver and get the AlarmManager service.

package de.vogella.android.alarm;

import android.app.Activity;
import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

public class AlarmActivity extends Activity {
 /** Called when the activity is first created. */
 @Override
 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
 }

 public void startAlert(View view) {
  EditText text = (EditText) findViewById(R.id.time);
  int i = Integer.parseInt(text.getText().toString());
  Intent intent = new Intent(this, MyBroadcastReceiver.class);
  PendingIntent pendingIntent = PendingIntent.getBroadcast(
    this.getApplicationContext(), 234324243, intent, 0);
  AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
  alarmManager.set(AlarmManager.RTC_WAKEUP, System.currentTimeMillis()
    + (i * 1000), pendingIntent);
  Toast.makeText(this, "Alarm set in " + i + " seconds",
    Toast.LENGTH_LONG).show();
 }

}
   

Run your application on the device. Set your time and start the alarm. After the defined number of seconds a Toast should be displayed. The vibrator alarm does not work on the simulator.

4. Define and consume your own service

The following will demonstrate how to create and consume a service from an activity. The service will periodically fetch data. The service will used by an activity which bind itself to the service. The activity will allow to request the latest data from the service.
Create a new project "de.vogella.android.ownservice" with the activity "ServiceConsumer".
Create a service "WordService" by create the class and the entry in "AndroidManifest.xml".

package de.vogella.android.ownservice;

import java.util.ArrayList;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;

import android.app.Service;
import android.content.Intent;
import android.os.Binder;
import android.os.IBinder;
import android.util.Log;

public class WordService extends Service {
 private Timer timer = new Timer();
 private static final long UPDATE_INTERVAL = 5000;
 private final IBinder mBinder = new MyBinder();
 private ArrayList<String> list = new ArrayList<String>();
 private String[] fixedList = { "Linux", "Android", "iPhone", "vogella.de",
   "helpful", "stuff" };
 private int index = 0;

 public void onCreate() {
  super.onCreate();
  pollForUpdates();
 }

 private void pollForUpdates() {
  timer.scheduleAtFixedRate(new TimerTask() {
   @Override
   public void run() {
    // Imagine here a freaking cool web access ;-)
    if (list.size() >= 6) {
     list.remove(0);
    }
    list.add(fixedList[index++]);
    if (index >= fixedList.length) {
     index = 0;
    }
   }
  }, 0, UPDATE_INTERVAL);
  Log.i(getClass().getSimpleName(), "Timer started.");

 }

 @Override
 public void onDestroy() {
  super.onDestroy();
  if (timer != null) {
   timer.cancel();
  }
  Log.i(getClass().getSimpleName(), "Timer stopped.");

 }

 // We return the binder class upon a call of bindService
 @Override
 public IBinder onBind(Intent arg0) {
  return mBinder;
 }

 public class MyBinder extends Binder {
  WordService getService() {
   return WordService.this;
  }
 }

 public List<String> getWordList() {
  return list;
 }

}

  


<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="de.vogella.android.ownservice"
      android:versionCode="1"
      android:versionName="1.0">
    <uses-sdk android:minSdkVersion="10" />

    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".ServiceConsumer"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <service android:name="WordService"></service>

    </application>
</manifest>
  

Change the layout "main.xml" to the following.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:orientation="vertical" android:layout_width="fill_parent"
 android:layout_height="fill_parent">
 <Button android:text="Reload Data" android:id="@+id/button1"
  android:layout_width="wrap_content" android:layout_height="wrap_content"
  android:onClick="showServiceData"></Button>
 <ListView android:id="@+id/list" android:layout_width="match_parent" android:layout_height="match_parent"></ListView>
</LinearLayout>

   

Change the activity ServiceConsumer to the following.

package de.vogella.android.ownservice;

import java.util.ArrayList;
import java.util.List;

import android.app.Activity;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

public class ServiceConsumer extends Activity {
 private WordService s;
 private ArrayList<String> values;

 /** Called when the activity is first created. */
 @Override
 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
  doBindService();
  values = new ArrayList<String>();
  adapter = new ArrayAdapter<String>(this,
    android.R.layout.simple_list_item_1, values);
  ListView list = (ListView) findViewById(R.id.list);
  list.setAdapter(adapter);

  // List<String> wordList = s.getWordList();
  // Toast.makeText(this, wordList.get(0), Toast.LENGTH_LONG).show();
 }

 private ServiceConnection mConnection = new ServiceConnection() {

  public void onServiceConnected(ComponentName className, IBinder binder) {
   s = ((WordService.MyBinder) binder).getService();
   Toast.makeText(ServiceConsumer.this, "Connected",
     Toast.LENGTH_SHORT).show();
  }

  public void onServiceDisconnected(ComponentName className) {
   s = null;
  }
 };
 private ArrayAdapter<String> adapter;

 void doBindService() {
  bindService(new Intent(this, WordService.class), mConnection,
    Context.BIND_AUTO_CREATE);
 }

 public void showServiceData(View view) {
  if (s != null) {
   List<String> wordList = s.getWordList();
   values.clear();
   values.addAll(wordList);
   adapter.notifyDataSetChanged();
  }
 }
}
  

5. Thank you

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