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Android BroadcastReceiver - Tutorial

Lars Vogel

Version 3.0

14.08.2013

Revision History
Revision 0.1 - 3.0 07.03.2011 - 14.08.2013 Lars
Vogel
bugs fixed and enhancements

Using BroadcastReceivers in Android

This tutorial describes how to create and consume Android services. It is based on Eclipse 4.3, Java 1.6 and Android 4.2.


Table of Contents

1. Broadcast receiver
1.1. Definition
1.2. Implementation
1.3. Life cycle of a broadcast receiver
1.4. Asynchronous processing
1.5. Restrictions for defining broadcast receiver
2. System broadcasts
3. Automatically starting Services from a Receivers
4. Pending Intent
5. Exercise: Define receiver for phone changes
5.1. Target
5.2. Create project
5.3. Implement receiver
5.4. Validate implementations
6. Exercise: System services and receiver
6.1. Target|
6.2. Implement project
6.3. Validate implementation
7. Defining custom events and receivers
7.1. Registering broadcast receiver for custom events
7.2. Sending broadcast intents
7.3. Local broadcast events with LocalBroadcastManager
8. Dynamic broadcast receiver registration
8.1. Dynamically registered receiver
8.2. Using the package manager to disable static receivers
8.3. Sticky (broadcast) intents
9. Support this website
9.1. Thank you
9.2. Questions and Discussion
10. Links and Literature
10.1. Source Code
10.2. Android Resources
10.3. vogella Resources

1. Broadcast receiver

1.1. Definition

A broadcast receiver (short receiver) is an Android component which allows you to register for system or application events. All registered receivers for an event are notified by the Android runtime once this event happens.

For example, applications can register for the ACTION_BOOT_COMPLETED system event which is fired once the Android system has completed the boot process.

1.2. Implementation

A receiver can be registered via the AndroidManifest.xml file.

Alternatively to this static registration, you can also register a receiver dynamically via the Context.registerReceiver() method.

The implementing class for a receiver extends the BroadcastReceiver class.

If the event for which the broadcast receiver has registered happens, the onReceive() method of the receiver is called by the Android system.

1.3. Life cycle of a broadcast receiver

After the onReceive() of the receiver class has finished, the Android system is allowed to recycle the receiver.

1.4. Asynchronous processing

Before API level 11, you could not perform any asynchronous operation in the onReceive() method, because once the onReceive() method had been finished, the Android system was allowed to recycle that component. If you have potentially long running operations, you should trigger a service instead.

Since Android API 11 you can call the goAsync() method. This method returns an object of the PendingResult type. The Android system considers the receiver as alive until you call the PendingResult.finish() on this object. With this option you can trigger asynchronous processing in a receiver. As soon as that thread has completed, its task calls finish() to indicate to the Android system that this component can be recycled.

1.5. Restrictions for defining broadcast receiver

As of Android 3.1 the Android system excludes all receiver from receiving intents by default if the corresponding application has never been started by the user or if the user explicitly stopped the application via the Android menu (in ManageApplication).

This is an additional security feature as the user can be sure that only the applications he started will receive broadcast intents.

Tip

This does not mean the user has to start the application again after a reboot. The Android system remembers that the user already started it. Only one start is required without a forced stop by the user.

2. System broadcasts

Several system events are defined as final static fields in the Intent class. Other Android system classes also define events, e.g., the TelephonyManager defines events for the change of the phone state.

The following table lists a few important system events.

Table 1. System Events

Event Description
Intent.ACTION_BOOT_COMPLETED Boot completed. Requires the android.permission.RECEIVE_BOOT_COMPLETED permission.
Intent.ACTION_POWER_CONNECTED Power got connected to the device.
Intent.ACTION_POWER_DISCONNECTED Power got disconnected to the device.
Intent.ACTION_BATTERY_LOW Triggered on low battery. Typically used to reduce activities in your app which consume power.
Intent.ACTION_BATTERY_OKAY Battery status good again.


3. Automatically starting Services from a Receivers

A common requirement is to automatically start a service after a system reboot, i.e., for synchronizing data. For this you can register a receiver for the android.intent.action.BOOT_COMPLETED system event. This requires the android.permission.RECEIVE_BOOT_COMPLETED permission.

The following example demonstrates the registration for the BOOT_COMPLETED event in the Android manifest file.

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

    <uses-sdk android:minSdkVersion="10" />

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

    <application
        android:icon="@drawable/icon"
        android:label="@string/app_name" >
        <activity
            android:name=".ServiceConsumerActivity"
            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="MyScheduleReceiver" >
            <intent-filter>
                <action android:name="android.intent.action.BOOT_COMPLETED" />
            </intent-filter>
        </receiver>
        <receiver android:name="MyStartServiceReceiver" >
        </receiver>
    </application>

</manifest> 

The receive would start the service as demonstrated in the following example code.

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;

public class MyReceiver extends BroadcastReceiver {

  @Override
  public void onReceive(Context context, Intent intent) {
    // assumes WordService is a registered service
    Intent intent = new Intent(context, WordService.class);
    context.startService(intent);
  }
} 

Tip

If your application is installed on the SD card, then it is not available after the android.intent.action.BOOT_COMPLETED event. In this case register it for the android.intent.action.ACTION_EXTERNAL_APPLICATIONS_AVAILABLE event.

Note

Remember that as of Android API level 11 the user needs to have started the application at least once before your application can receive android.intent.action.BOOT_COMPLETED events.

4. Pending Intent

A pending intent 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, get a PendingIntent via the getBroadcast() method of the PendingIntent class. To perform an activity via a pending intent, you receive the activity via PendingIntent.getActivity().

5. Exercise: Define receiver for phone changes

5.1. Target

In this exercise you 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.

5.2. Create project

Create a new project called de.vogella.android.receiver.phone. Also create an activity.

Tip

Remember that your receiver is only called if the user started it once. This requires an activity.

5.3. Implement receiver

Register your receiver in your AndroidManifest.xml file similar to the following listing.

<?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" >

     <uses-sdk android:minSdkVersion="15" />
     
    <uses-permission android:name="android.permission.READ_PHONE_STATE" >
    </uses-permission>

    <application
        android:icon="@drawable/icon"
        android:label="@string/app_name" >
           <activity
            android:name=".MainActivity"
            android:label="@string/title_activity_main" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        
        <receiver android:name="MyPhoneReceiver" >
            <intent-filter>
                <action android:name="android.intent.action.PHONE_STATE" >
                </action>
            </intent-filter>
        </receiver>
    </application>

   

</manifest> 

Create the MyPhoneReceiver class.

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("MY_DEBUG_TAG", state);
      if (state.equals(TelephonyManager.EXTRA_STATE_RINGING)) {
        String phoneNumber = extras
            .getString(TelephonyManager.EXTRA_INCOMING_NUMBER);
        Log.w("MY_DEBUG_TAG", phoneNumber);
      }
    }
  }
} 

5.4. Validate implementations

Install your application and simulate a phone call via the DDMS perspective in Eclipse. Validate that your receiver is called and logs a message to the LogCat view.

6. Exercise: System services and receiver

6.1. Target|

In this chapter we will schedule a receiver via the Android alert manager system service. Once called, it uses the Android vibrator manager and a popup message (Toast) to notify the user.

6.2. Implement project

Create a new project called de.vogella.android.alarm with the activity called AlarmActivity.

Create the following layout.

<?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" >

    <EditText
        android:id="@+id/time"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:hint="Number of seconds"
        android:inputType="numberDecimal" >
    </EditText>

    <Button
        android:id="@+id/ok"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="startAlert"
        android:text="Start Counter" >
    </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);
  }

} 

Register this class as a broadcast receiver in AndroidManifest.xml and request authorization to vibrate the phone.

<?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="15" />

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

    <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>

</manifest> 

Change the code of your AlarmActivity class to the following. This activity creates an intent to start the receiver and register this intent with the alarm manager 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(); } }

6.3. Validate implementation

Run your application on the device. Set your time and start the alarm. After the defined number of seconds a Toast should be displayed. Keep in mind that the vibration alarm does not work on the Android emulator.

Alarm application running

7. Defining custom events and receivers

7.1. Registering broadcast receiver for custom events

You can register a receiver for your custom actions.

The following AndroidManifest.xml file demonstrates a broadcast receiver which is registered for a custom action.

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

    <uses-sdk android:minSdkVersion="15" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:name=".MainActivity"
            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="MyReceiver" >
            <intent-filter>
                <action android:name="de.vogella.android.mybroadcast" />
            </intent-filter>
        </receiver>
    </application>

</manifest> 

7.2. Sending broadcast intents

The sendBroadcast() method from the Context class allows you to send intents to your registered receivers. The following coding show an example.

Intent intent = new Intent();
intent.setAction("de.vogella.android.mybroadcast");
sendBroadcast(intent); 

You cannot trigger system broadcasts events. The Android system will prevent this.

Tip

The receivers are called asynchronous, i.e., the sendBroadcast() method return immediately and does not wait until the receivers have executed.

7.3. Local broadcast events with LocalBroadcastManager

The LocalBroadcastManager class is used to register for and send broadcasts of Intents to local objects within your process. This is faster and more secure as your events don't leave your application.

The following example shows an activity which registers for a customer event called my-event.

@Override
public void onResume() {
  super.onResume();

  // Register mMessageReceiver to receive messages.
  LocalBroadcastManager.getInstance(this).registerReceiver(mMessageReceiver,
      new IntentFilter("my-event"));
}

// handler for received Intents for the "my-event" event 
private BroadcastReceiver mMessageReceiver = new BroadcastReceiver() {
  @Override
  public void onReceive(Context context, Intent intent) {
    // Extract data included in the Intent
    String message = intent.getStringExtra("message");
    Log.d("receiver", "Got message: " + message);
  }
};

@Override
protected void onPause() {
  // Unregister since the activity is not visible
  LocalBroadcastManager.getInstance(this).unregisterReceiver(mMessageReceiver);
  super.onPause();
} 

// This method is assigned to button in the layout
// via the onClick property
public void onClick(View view) {
  sendMessage();
}

// Send an Intent with an action named "my-event". 
private void sendMessage() {
  Intent intent = new Intent("my-event");
  // add data
  intent.putExtra("message", "data");
  LocalBroadcastManager.getInstance(this).sendBroadcast(intent);
} 

8. Dynamic broadcast receiver registration

8.1. Dynamically registered receiver

Receiver can be registered via the Android manifest file. You can also register and unregister a receiver at runtime via the Context.registerReceiver() and Context.unregisterReceiver() methods.

Warning

Do not forget to unregister a dynamically registered receiver by using Context.unregisterReceiver() method. If you forget this, the Android system reports a leaked broadcast receiver error. For instance, if you registered a receive in onResume() methods of your activity, you should unregister it in the onPause() method.

8.2. Using the package manager to disable static receivers

You can use the PackageManager class to enable or disable receivers registered in your AndroidManifest.xml file.

ComponentName receiver = new ComponentName(context, myReceiver.class);
PackageManager pm = context.getPackageManager();

pm.setComponentEnabledSetting(receiver, 
  PackageManager.COMPONENT_ENABLED_STATE_ENABLED,
  PackageManager.DONT_KILL_APP); 

8.3. Sticky (broadcast) intents

An intent to trigger a receiver (broadcast intent) is not available anymore after it was sent and processed by the system. If you use the sendStickyBroadcast(Intent) method, the corresponding intent is sticky, meaning the intent you are sending stays around after the broadcast is complete.

The Android system uses sticky broadcast for certain system information. For example, the battery status is send as sticky intent and can get received at any time. The following example demonstrates that.

// Register for the battery changed event
IntentFilter filter = new IntentFilter(Intent.ACTION_BATTERY_CHANGED);

/ Intent is sticky so using null as receiver works fine
// return value contains the status
Intent batteryStatus = this.registerReceiver(null, filter);

// Are we charging / charged?
int status = batteryStatus.getIntExtra(BatteryManager.EXTRA_STATUS, -1);
boolean isCharging = status == BatteryManager.BATTERY_STATUS_CHARGING
  || status == BatteryManager.BATTERY_STATUS_FULL;

boolean isFull = status == BatteryManager.BATTERY_STATUS_FULL;

// How are we charging?
int chargePlug = batteryStatus.getIntExtra(BatteryManager.EXTRA_PLUGGED, -1);
boolean usbCharge = chargePlug == BatteryManager.BATTERY_PLUGGED_USB;
boolean acCharge = chargePlug == BatteryManager.BATTERY_PLUGGED_AC; 

You can retrieve that data through the return value of registerReceiver(BroadcastReceiver, IntentFilter) . This also works for a null BroadcastReceiver.

In all other ways, this behaves just as sendBroadcast(Intent).

Sticky broadcast intents typically require special permissions.

9. Support this website

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.

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.

9.1. Thank you

Please consider a contribution if this article helped you.

Flattr this

9.2. Questions and Discussion

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.

10. Links and Literature

10.1. Source Code

Source Code of Examples

10.3. vogella Resources

vogella Training Android and Eclipse Training from the vogella team

Android Tutorial Introduction to Android Programming

GWT Tutorial Program in Java, compile to JavaScript and HTML

Eclipse RCP Tutorial Create native applications in Java

JUnit Tutorial Test your application

Git Tutorial Put all your files in a distributed version control system