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 2

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 3

Broadcasting an Event Two step process:::: 1. Build the intent for Broadcast 2. Broadcast the built intent 4

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); 5

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. Register in manifest 2. Register in code 6

Listening for Broadcasts  While registering as a BroadcastReceiver a class must specify the intent-filter to describe which event this class is listening for 7

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

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. } 9

BroadcastReceiver in XML ………………….. 10 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); } 11

Receiver Example Manifest 12

Registering Receiver in Code IntentFilter filter = new IntentFilter(string-event); MyBroadcastReceiver receiver = new MyBroadcastReceiver(); registerReceiver(receiver, filter); 13

Unregister a Receiver unregisterReceiver(receiver); 14

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-hours 2. When phone screen is turned on/off during night 3. …………… 15

Native Android Broadcast Events ACTION_BOOT_COMPLETEDFired once when the device has completed its startup sequence. An application requires the RECEIVE_BOOT_COMPLETED permission to receive this broadcast ACTION_CAMERA_BUTTONFired 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. 16

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_CALLBroadcast 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_CHANGEDThis 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. 17

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. 18

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); 19

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. 20

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. 21

Pending Intent Example (Main.xml) <LinearLayout xmlns:android=… android:orientation="vertical“ android:layout_width="fill_parent“ android:layout_height="fill_parent"> <EditText android:layout_height="wrap_content" android:layout_width="wrap_content" android:hint="Number of seconds" android:inputType="numberDecimal"/> 22 <Button android:text="Start Counter" android:onClick="startAlert" android:layout_width="wrap_content" android:layout_height="wrap_content” />

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); } 23

Pending Intent Example (Main.java) public class Main extends Activity { EditText time; /** Called when the activity is first created. public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } 24

Pending Intent Example (Manifest) 25