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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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Broadcasting
 System
level message sending mechanism
 Structured message sending across applications
 Intents can be used to send messages across applications
via sendBroadcast() method
 Broadcast 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 Event
Two step process::::
1. Build the intent for Broadcast
2. 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 Broadcasts
 BroadcastReceiver
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.
2.
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Register in manifest
Register in code
Listening for Broadcasts
 While
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 BroadcastReceiver
public class MyBroadcastReceiver extends BroadcastReceiver{
public void onReceive(Context c, Intent intent){
//Some code to handle the event
}//End of onReceive
} //End of MyBroadcastReceiver
onReceive() function is called automatically when
event-generated is matched with the one described
in intent-filter tag.
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onReceive() example
public 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>
Receiver registered in xml (manifest) will always be
active (even if application is not running/application is
in background)
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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 Code
IntentFilter 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.
2.
3.
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Listening for outgoing calls during office-hours
When phone screen is turned on/off during night
……………
Native Android Broadcast Events
ACTION_BOOT_COMPLETED
Fired once when the device has completed
its startup sequence. An
application requires the
RECEIVE_BOOT_COMPLETED
permission to receive this broadcast
ACTION_CAMERA_BUTTON
Fired when camera button is clicked
ACTION_DATE_CHANGED
ACTION_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 broadcast
whenever 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_OFF
ACTION_SCREEN_ON
Broadcast when the screen turns off or on
Respectively.
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 Activity
Intent startIntent = new Intent(this, OtherActivity.class);
PendingIntent.getActivity(this, 0, startIntent , 0);
// Broadcast an Intent
Intent broadcastIntent = new
Intent(NEW_LIFEFORM_DETECTED);
PendingIntent.getBroadcast(this, 0, broadcastIntent, 0);
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Pending Intent
It 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 Intent
If 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 phone
Vibrator 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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