LECTURE 12 BROADCAST RECEIVERS

Transcription

1 MOBILE APPLICATION DEVELOPMENT LECTURE 12 BROADCAST RECEIVERS IMRAN IHSAN ASSISTANT PROFESSOR Application Building Blocks Android Component Activity UI Component Typically Corresponding to one screen. Intent Receiver Responds to notifications or status changes. Can wake up your process. Service Faceless task that runs in the background. ContentProvider Enable applications to share data. 1

2 Application Building Blocks Android Component Activities 1. Provides User Interface 2. Usually represents a Single Screen 3. Can contain one/more Views 4. Extends the Activity Base class Services 1. No User Interface 2. Runs in Background 3. Extends the Service Base Class Application= Set of Android Components Intent/Broadcast Receiver 1. Receives and Reacts to broadcast Intents 2. No UI but can start an Activity 3. Extends the BroadcastReceiver Base Class Content Provider 1. Makes application data available to other apps 2. Data stored in SQLite database 3. Extends the ContentProvider Base class Broadcast Receivers Android Component A broadcast receiver is a component that responds to system-wide Broadcast announcements. Many broadcasts originate from the system for example, a Broadcast announcing that the screen has turned off, the battery is low, or a picture was captured or an SMS is received. Applications can also initiate broadcasts for example, to let other Applications know that some data has been downloaded to the device and is available for them to use. Although broadcast receivers don't display a user interface, they may create a status bar notification to alert the user when a broadcast event occurs. More commonly, though, a broadcast receiver is just a "gateway" to other components and is intended to do a very minimal amount of work. For instance, it might initiate a service/or start an activity to perform some work based on the event. 2

3 Broadcast Receivers Android Component Android Application Anatomy Big Picture Activity 1 Activity 2 UI Service BroadcastReceiver Intents BIG PICTURE OS 3

4 Android Application Anatomy Big Picture 1. We ll use a Broadcast Receiver to capture SMS receive event 2. We capture the SMS receive event and launch an Activity to show the SMS and give user an option to reply the SMS Activity OS BroadcastReceiver Broadcast Receivers SMS Application 1. Create a new project BroadcastReceiverDemo 2. A broadcast receiver is implemented as a subclass of BroadcastReceiver and each broadcast is delivered as an Intent object. In this case the intent is detected by android.provider.telephony.sms_received To do this we ll create a class SMSReceiver that extends BroadcastReceiver class and define the method onreceive() 4

5 Broadcast Receivers SMS Application 3. We also need to add SMSReceiver as receiver of a particular Intent (SMS received) which is identified by android.provider.telephony.sms_received Broadcast Receivers SMS Application 4. Also we have to add permission for receiving SMS 5

6 Broadcast Receivers SMS Application 5. Now we run the application 6. Now we use emulator control to send sms Receiving SMS Broadcast Receiver public void onreceive(context context, Intent intent) { Bundle bundle = intent.getextras(); SmsMessage smsmessage; try { if ( bundle!= null) { if (Build.VERSION.SDK_INT >= 19 ) { //kitkat SmsMessage[] msgs = Telephony.Sms.Intents.getMessagesFromIntent(intent); smsmessage = msgs[0]; else { Object[] objpdus = (Object[]) bundle.get("pdus"); smsmessage = SmsMessage.createFromPdu((byte[])objPdus[0]); String phonenumber = smsmessage.getdisplayoriginatingaddress(); String message = smsmessage.getmessagebody(); Toast.makeText(context, "SenderNum: \n " + phonenumber + "; message: \n " + message, Toast.LENGTH_LONG).show(); catch (Exception e) { e.printstacktrace(); 6

7 Sending SMS Broadcast Receiver 1. Add permission in menifest.xml 2. We add the following code for sending SMS from anywhere of our application Registering BroadcastReceivers Two ways to register 1. Statically AndroidManifest.XML 2. Dynamically Context.registerReceiver() 7

8 Static Registration Two ways to register Include <receiver> in AndroidManifest.xml <application> <receiver receiver specs > <intent-filter> event specs </intent-filter> </receiver> </application> Receiver registered at boot time or when application package is added Static Registration (cont.) Two ways to register <receiver android:name=".incomingsms" android:enabled = "true"> <intent-filter android:priority="1000"> <action android:name= "android.provider.telephony.sms_received" /> </intent-filter> </receiver> 8

9 Dynamic Registration Dynamic 1. Create an IntentFilter 2. Create a BroadcastReceiver 3. Register BroadcastReceiver to receive Intents using Context.registerReceiver() 4. When appropriate call Context.unRegisterReceiver() to unregister BroadcastReceiver Dynamic Registration Dynamic public class SingleBroadcast extends Activity { public static final String CUSTOM_INTENT = "course.examples.broadcastreceiver.intent.action.test1"; final Receiver1 br1 = new Receiver1(); final IntentFilter intfil = new IntentFilter(CUSTOM_INTENT); public void oncreate(bundle savedinstancestate) { Button button = (Button) findviewbyid(r.id.button); button.setonclicklistener(new OnClickListener() { public void onclick(view v) { sendbroadcast(new Intent(CUSTOM_INTENT), android.manifest.permission.vibrate); ); registerreceiver(br1, intfil); 9

10 Dynamic Registration protected void ondestroy() { unregisterreceiver(br1); super.ondestroy(); Event Broadcast Broadcast Events Several broadcast methods supported Normal vs. Ordered Normal: processing order undefined Ordered: sequential processing in priority order Sticky vs. Non-Sticky Sticky: Store Event after initial broadcast Non-Sticky: Discard Event after initial broadcast 10

11 Normal Broadcasts Broadcast Events //public abstract class Context // send Intent to interested BroadcastReceivers void sendbroadcast (Intent intent) // send Intent to interested BroadcastReceivers // if they have the specified permissions void sendbroadcast (Intent intent, String receiverpermission) Normal Broadcasts (cont.) Broadcast Events public class SimpleBroadcast extends Activity { public static final String CUSTOM_INTENT = "course.examples.broadcastreceiver.intent.action.test2"; public void oncreate(bundle savedinstancestate) { Button button = (Button) findviewbyid(r.id.button); button.setonclicklistener(new OnClickListener() public void onclick(view v) { sendbroadcast(new Intent(CUSTOM_INTENT), android.manifest.permission.vibrate); ); 11

12 Ordered Broadcasts Broadcast Events //public abstract class Context // send Intent to interested BroadcastReceivers in priority order void sendorderedbroadcast (Intent intent, String receiverpermission) // send Intent to interested BroadcastReceivers in priority order // sender can provide various parameters for greater control void sendorderedbroadcast (Intent intent, String receiverpermission, BroadcastReceiver resultreceiver, Handler scheduler, int initialcode, String initialdata, Bundle initialextras) Ordered Broadcasts (cont.) Broadcast Events public class CompoundOrderedBroadcast extends Activity { public static final String CUSTOM_INTENT = "course.examples.broadcastreceiver.intent.action.test4 "; public void oncreate(bundle savedinstancestate) { Button button = (Button) findviewbyid(r.id.button); button.setonclicklistener(new OnClickListener() public void onclick(view v) { sendorderedbroadcast(new Intent(CUSTOM_INTENT),android.Manifest.permission.VIBRATE); ); 12

13 Ordered Broadcasts (cont.) Broadcast Events public class CompoundOrderedBroadcastWithResultReceiver extends Activity { public static final String CUSTOM_INTENT = "course.examples.broadcastreceiver.intent.action.test4"; public void oncreate(bundle savedinstancestate) { Button button = (Button) findviewbyid(r.id.button); button.setonclicklistener(new OnClickListener() public void onclick(view v) { sendorderedbroadcast(new Intent(CUSTOM_INTENT), null, new BroadcastReceiver() public void onreceive(context context, Intent intent) { System.out.println("Final Result is:" + getresultdata());, null, 0, null, null); ); Sticky Broadcasts Sticky Events sent as sticky broadcasts are cached by Android New intents overwrite older intents they match When later a BroadcastReceiver is registered dynamically Cached sticky Intents matching the specified IntentFilter are broadcast to the BroadcastReceiver One matching sticky Intent is returned to the caller 13

14 Sticky Broadcasts (Cont.) Sticky Events //public abstract class Context // send sticky Intent to interested BroadcastReceivers void sendstickybroadcast (Intent intent) // send sticky Intent to interested BroadcastReceivers in priority order // sender can provide various parameters for greater control void sendstickyorderedbroadcast (Intent intent, BroadcastReceiver resultreceiver, Handler scheduler, int initialcode, String initialdata, Bundle initialextras) Must have BROADCAST_STICKY permission to send sticky Intents Intent Filter Matching Sticky Similar to matching for Activities & Services Some debugging tips Log BroadcastReceivers that match an Intent Intent.setFlag(FLAG_DEBUG_LOG_RESOLUTI ON) Print BroadcastReceivers registered to receive intents Dynamic registration % adb shell dumpsys activity b Static registration % adb shell dumpsys package 14

15 Event Delivery Broadcast Events Events delivered by calling onreceive() Event Handling in onreceive() Broadcast Events onreceive() should be short-lived Hosting process has high priority while onreceive() is executing & is often when onreceive() returns If event handling take a long time, consider starting a Service, rather than performing complete operation in onreceive() BroadcastReceivers can t start asynchronous operations e.g., showing a dialog, binding to a Service, starting an Activity via startactivityforresult 15

16 Handling a Normal Broadcast onreceive() public class Receiver2 extends BroadcastReceiver public void onreceive(context context, Intent intent) { System.out.println(this + ":GOT THE INTENT"); // emulator doesn't support vibration Vibrator v = (Vibrator) context.getsystemservice(context.vibrator_service); v.vibrate(500); Handling an Ordered Broadcast onreceive() Passing results public class Receiver1 extends BroadcastReceiver public void onreceive(context context, Intent intent) { String tmp = getresultdata()!= null? getresultdata() : ""; setresultdata(tmp + ":Receiver 1:"); 16

17 Handling an Ordered Broadcast onreceive() Aborting the Broadcast public class Receiver2 extends BroadcastReceiver public void onreceive(context context, Intent intent) { if (isorderedbroadcast()) { System.out.println(this + ":Calling abortbroadcast()"); abortbroadcast(); System.out.println(this + ":GOT THE INTENT"); // emulator doesn't support vibration Vibrator v = (Vibrator) context.getsystemservice(context.vibrator_service); v.vibrate(500); Handling a Sticky Broadcast onreceive() public class StickyIntentBroadcastReceiverActivity extends Activity public void oncreate(bundle savedinstancestate) { super.oncreate(savedinstancestate); setcontentview(r.layout.main); final TextView state = (TextView) findviewbyid(r.id.level); registerreceiver(new BroadcastReceiver() public void onreceive(context context, Intent intent) { 17

18 Handling a Sticky Broadcast (Cont.) onreceive() If (intent.getaction().equals( Intent.ACTION_BATTERY_CHANGED)) { String age = "Reading taken recently"; if (isinitialstickybroadcast()) { age = "Reading may be stale"; state.settext("current Battery Level" + String.valueOf(intent.getIntExtra( BatteryManager.EXTRA_LEVEL, -1)) + "\n" + age);, new IntentFilter(Intent.ACTION_BATTERY_CHANGED)); Questions? 18