Mobile Computing

Lecture#08 IntentFilters & BroadcastReceivers

Lecture Contents Intent Filters for Plug-ins/Extensibility Annonymous Actions to Applications Intents to Broadcast Events Listening for Broadcasts Broadcast Receivers BroadcastReceivers in Code BroadcastReceivers in XML Native Android Broadcast Actions

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BroadcastingSystem level message sending mechanismStructured message sending across

applications Intents can be used to send messages across

applications via sendBroadcast() methodBroadcast intents extend the event driven

approach (all applications on a system may behave like event handlers)

Applications registered to handle an event can react to that event without causing any change in event generating application

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Broadcasting an EventTwo step process::::1. Build the intent for Broadcast2. Broadcast the built intent

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Android Code

public static final String new_life_appeared = “com.test.lives.NEW_LIFE”;

Intent intent = new Intent(new_life_appeared);intent.putExtra(“type”, “human_life”);intent.putExtra(“where”, “unknown_location”);……..……..sendBroadcast(intent);

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Listening for BroadcastsBroadcastReceiver is a instance of a class that

has registered itself as receiver for a particular broadcast event

For a class to work as a BroadcastRegister, it must register itself as BroadcastReceiver

Two methods to register::1. Register in manifest2. Register in code

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Listening for BroadcastsWhile registering as a BroadcastReceiver a

class must specify the intent-filter to describe which event this class is listening for

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Creating a BroadcastReceiverpublic class MyBroadcastReceiver extends

BroadcastReceiver{

public void onReceive(Context c, Intent intent){//Some code to handle the event}//End of onReceive

} //End of MyBroadcastReceiver

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onReceive() function is called automatically when event-generated is matched with the one described in intent-filter tag.

onReceive() examplepublic void onReceive(Context context, Intent

intent){Uri data = intent.getData();String type = intent.getStringExtra(“type”);…………Typically launch some activity/service to perform

some action based on the intent received.

}

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BroadcastReceiver in XML<receiver

android:name=“com.test.MyBroadcastReceiver”><intent-filter>

<action android:name=“…….”>…………………..

</intent-filter></receiver>

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Receiver registered in xml (manifest) will always be active (even if application is not running/application is in background)

Receiver Example Code

public void onReceive(Context context, Intent intent){

Bundle extras = intent.getExtras();

if (extras != null) {

String state = extras.getString(TelephonyManager.EXTRA_STATE);

if (state.equals(TelephonyManager.EXTRA_STATE_RINGING)) {String phoneNumber = extras.getString(TelephonyManager.EXTRA_INCOMING_NUMBER);

Log.i(tag+":Number", phoneNumber);

}}

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Receiver Example Manifest <receiver

android:name="com.braodcast.receiver.MyPhoneReceiver"><intent-filter>

<action android:name="android.intent.action.PHONE_STATE">

</action></intent-filter>

</receiver>

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Registering Receiver in CodeIntentFilter filter = new IntentFilter(string-

event);MyBroadcastReceiver receiver = new

MyBroadcastReceiver();registerReceiver(receiver, filter);

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Unregister a Receiver

unregisterReceiver(receiver);

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Dynamic Receiver

A receiver can register as a receiver for any global event for a particular period of time and later can unregister when span of interest is gone.1. Listening for outgoing calls during office-hours2. When phone screen is turned on/off during night 3. ……………

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Native Android Broadcast Events

ACTION_BOOT_COMPLETED Fired once when the device has completed its startup sequence. Anapplication requires the RECEIVE_BOOT_COMPLETED permission to receive this broadcast

ACTION_CAMERA_BUTTON Fired when camera button is clicked

ACTION_DATE_CHANGEDACTION_TIME_CHANGED

Fired when system’s date/time is changed manually

ACTION_MEDIA_EJECT If the user chooses to eject the external storage media, this event is fired first. If your application is reading or writing to the external media storage you should listen for this event in order to save and close any open file handles.

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Native Android Broadcast Events

ACTION_MEDIA_MOUNTED ACTION_MEDIA_UNMOUNTED

These two events are broadcastwhenever new external storage media are successfully added to or removed from the device.

ACTION_NEW_OUTGOING_CALL Broadcast when a new outgoing call is about to be placed. Listen for this broadcast to intercept outgoing calls.

ACTION_SCREEN_OFFACTION_SCREEN_ON

Broadcast when the screen turns off or onRespectively.

ACTION_TIMEZONE_CHANGED This action is broadcast whenever the phone’s current time zone changes. The Intent includes a time-zone extra that returns the ID of the new java.util.TimeZone.

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Pending Intents The PendingIntent class provides a

mechanism for creating Intents that can be fired by another applicationat a later time.

A Pending Intent is commonly used to package an Intent that will be fired in response to a future event, such as a widget View being clicked or a Notification being selected from the notification panel.

PendingIntent class offers static methods to construct Pending Intents used to start an Activity, start a Service, or broadcast an Intent.

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Pending Intents// Start an ActivityIntent startIntent = new Intent(this,

OtherActivity.class);PendingIntent.getActivity(this, 0, startIntent , 0);// Broadcast an IntentIntent broadcastIntent = new

Intent(NEW_LIFEFORM_DETECTED);PendingIntent.getBroadcast(this, 0, broadcastIntent,

0);

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Pending IntentIt is a token that you give to a foreign

application (e.g. Notification Manager, Alarm Manager, Home Screen AppWidget Manager, or other 3rd party applications), which allows a foreign application to use your application's permissions to execute a predefined piece of code.

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Pending IntentIf you give the foreign application an Intent, and

that application sends/broadcasts the Intent you gave, they will execute the Intent with their own permissions. But if you instead give the foreign application a Pending Intent you created using your own permission, that application will execute the contained Intent using your application's permission.

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Pending Intent Example (Main.xml)<?xml version="1.0" encoding="utf-

8"?>

<LinearLayout

xmlns: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"/>

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

Pending Intent Example (TimerReceiver.java)public class TimerReceiver extends BroadcastReceiver {

public void onReceive(Context context, Intent intent){

Toast.makeText(context, “Your time is up", Toast.LENGTH_LONG).show();

// Vibrate the mobile phoneVibrator vibrator = (Vibrator) context.getSystemService(Context.VIBRATOR_SERVICE);vibrator.vibrate(2000);}

}

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Pending Intent Example (Main.java)public class Main extends Activity {

EditText time;

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

}

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Pending Intent Example (Manifest)

<receiver android:name=".TimerReceiver"></receiver>

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

</uses-permission>

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