S2 M1 P4 Android IntentService

Douglas C. Schmidt [email protected]

www.dre.vanderbilt.edu/~schmidt

Professor of Computer Science Institute for Software Integrated Systems

Vanderbilt University

Nashville, Tennessee, USA

Android Services & Security: Android IntentService

mailto:[email protected]


2

Learning Objectives in this Part of the Module • Understand how the Android IntentService provides a framework for

programming Started Services that concurrently process commands expressed as Intents

developer.android.com/reference/android/app/IntentService.html has more

http://developer.android.com/reference/android/app/IntentService.html


3

Dequeue Intent

& get file

Motivation for IntentService • IntentService codifies an

idiom used in Android 1

Intent

onCreate()

onStartCommand()

Download Service

send intent startService()

Download Activity

Service Handler

4 3

2

downloadImageAndReply()

handleMessage()

See previous part on “Programming Started Services”

5

sendMessage()


4

Dequeue Intent

& get file


idiom used in Android 1

Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2

downloadImageAndReply()

handleMessage() 5

sendMessage()


5


idiom used in Android • Service.onCreate()

1

Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2

handleMessage()

void onCreate() { ... HandlerThread thread = new HandlerThread("DownloadService"); thread.start(); mServiceLooper = thread.getLooper(); mServiceHandler = new ServiceHandler(mServiceLooper); ...

Dequeue Intent

& get file

downloadImageAndReply() 5

sendMessage()


6



1. Create/start a HandlerThread

1

Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2

handleMessage()


Dequeue Intent

& get file


sendMessage()


7



1. Create/start a HandlerThread 2. Give the Thread-specific Looper

to an instance of a ServiceHandler

1

Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2

handleMessage()


Dequeue Intent

& get file


sendMessage()


8


idiom used in Android • Service.onCreate() • Service.onStartCommand()

1

Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2

handleMessage() int onStartCommand(Intent intent, int f, int startId) { Message msg = mServiceHandler.obtainMessage(); msg.arg1 = startId; msg.obj = intent; mServiceHandler.sendMessage(msg); ...

Dequeue Intent

& get file


sendMessage()


9



1.Create a Message encapsulating the Intent parameter

1

Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2


Dequeue Intent

& get file


sendMessage()


10



1.Create a Message encapsulating the Intent parameter

2.Send Message to ServiceHandler

1

Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2

sendMessage()


Dequeue Intent

& get file



11


idiom used in Android • Service.onCreate() • Service.onStartCommand() • ServiceHandler.handleMessage()

1

Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2

handleMessage()

void handleMessage(Message msg) { downloadImageAndReply ((Intent) msg.obj); stopSelf(msg.arg1);

Dequeue Intent

& get file


sendMessage()


12



1. Process the Message containing the Intent

1

Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2

handleMessage()


Dequeue Intent

& get file


sendMessage()


13



1. Process the Message containing the Intent 2. Have the Service stop itself

1

Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2

handleMessage()


Dequeue Intent

& get file


sendMessage()


14


idiom used in Android • This idioms appears in a number

of packaged applications, e.g. • packages/apps/Calendar/src/com/ android/calendar/alerts/ AlertService.java

• packages/apps/Mms/src/com/ android/mms/transaction/ SmsReceiverService.java

• packages/apps/Mms/src/com/ android/mms/transaction/ TransactionService.java

1

Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2

sendMessage()

handleMessage()

Dequeue Intent

& get file



15


idiom used in Android • This idioms appears in a number

of packaged applications, e.g. • packages/apps/Calendar/src/com/ android/calendar/alerts/ AlertService.java

• packages/apps/Mms/src/com/ android/mms/transaction/ SmsReceiverService.java

• packages/apps/Mms/src/com/ android/mms/transaction/ TransactionService.java

1

Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2

sendMessage()

handleMessage()

Dequeue Intent

& get file



16

Overview of the IntentService

(Part 1)


17

Overview of IntentService • IntentService codifies the idiom

for concurrent processing of Intents into a framework

public class IntentService extends Service { ... protected abstract void onHandleIntent(Intent intent); }


18


for concurrent processing of Intents into a framework

developer.android.com/reference/android/app/IntentService.html has more


http://developer.android.com/reference/android/app/IntentService.html


19


for concurrent processing of Intents into a framework • It’s very easy to use

Subclasses simply override this hook method to process an Intent

in a single background Thread



20

• IntentService codifies the idiom for concurrent processing of Intents into a framework

• Clients send Intents via calls to startService()

Overview of IntentService

See previous parts on “Programming Started Services”

1 Client

Intent Service

onCreate()

onStartCommand()

…

send intent

process intent

4

startService()

Download Service

onHandleIntent()

2

3

queue intent

dequeue intent

Service Handler

sendMessage()

handleMessage()

Intent


21



1 Client send intent startService()

Overview of IntentService Intent


22


• Clients send Intents via calls to startService() • Data & objects can be

passed to the Service by putting “extras” into Intents

1 Client send intent startService()


www.itcuties.com/android/intent-putextra has more info on extras

Intent

http://www.itcuties.com/android/intent-putextra


23

1


• Clients send Intents via calls to startService() • Data & objects can be

passed to the Service by putting “extras” into Intents

• The IntentService is launched on-demand via the Activator pattern

Client

Intent Service

onCreate()

onStartCommand()

www.dre.vanderbilt.edu/~schmidt/PDF/Activator.pdf has more on Activator



http://www.dre.vanderbilt.edu/~schmidt/PDF/Activator.pdf


24

1



• A subclass of IntentService implements onHandleIntent() • This hook method processes

the Intent sent by the client in a background Thread

Client

Intent Service

onCreate()

onStartCommand()

Download Service

onHandleIntent()

…



developer.android.com/guide/components/services.html#ExtendingIntentService

http://developer.android.com/guide/components/services.html#ExtendingIntentService


25

1





Client

Intent Service

onCreate()

onStartCommand()

Download Service

onHandleIntent()

…



void onHandleIntent(Intent intent) { downloadImageAndReply(intent); }


26

1





Client

Intent Service

onCreate()

onStartCommand()

Download Service

onHandleIntent()

…



void onHandleIntent(Intent intent) { downloadImageAndReply(intent); }


27

Overview of the IntentService

(Part 2)


28

1



• A subclass of IntentService implements onHandleIntent()

• The IntentService does several things

Client

Intent Service

onCreate()

onStartCommand()

2

…

3

send intent

queue intent

dequeue intent process intent

4

startService()


Download Service

onHandleIntent()

Service Handler

sendMessage()

handleMessage()

frameworks/base/core/java/android/os/IntentService.java has the code

Intent


29

1




• The IntentService does several things • Creates a ServiceHandler

Client

Intent Service

onCreate()

onStartCommand()

2

…

3

send intent

queue intent


4

startService()


Download Service

onHandleIntent()

Service Handler

sendMessage()

handleMessage()

Intent


30

1





Client

Intent Service

onStartCommand()

2

…

3

send intent

queue intent


4

startService()


Download Service

onHandleIntent()

Service Handler

sendMessage()

handleMessage()

Intent

onCreate()


31

1





• Internally creates a single background thread

Client

Intent Service

onCreate()

onStartCommand()

2

…

3

send intent

queue intent


4

startService()


Download Service

onHandleIntent()

Service Handler

sendMessage()

handleMessage()

Intent


32

1

onStartCommand()




• The IntentService does several things • Creates a ServiceHandler • Receives & queues

Intents in ServiceHandler

Client

Intent Service



onCreate()

…

process intent

4 onHandleIntent()

Download Service

2

3

queue intent

dequeue intent

Service Handler

sendMessage()

handleMessage()

Intent


33

1





Intents in ServiceHandler

Client

Intent Service



onCreate()

…

process intent

4 onHandleIntent()

Download Service

2

3

queue intent

dequeue intent

Service Handler

sendMessage()

handleMessage()

Intent

onStartCommand()


34

1





Intents in ServiceHandler • Processes the Intents “in

the background”

Client

Intent Service



onCreate()

…

process intent

4 onHandleIntent()

Download Service

2

3

queue intent

dequeue intent

Service Handler

sendMessage()

handleMessage()

Intent

onStartCommand()


35

1






the background”

Client

Intent Service



onCreate()

…

process intent

4 onHandleIntent()

Download Service

2

3

queue intent

dequeue intent

Service Handler

sendMessage()

handleMessage()

Intent

Only one Intent processed at a time by the one & only Thread

onStartCommand()


36

1






the background” • Stops Service when there are no more Intents to process

Client

Intent Service

onCreate()

onStartCommand()

…

send intent

process intent

4

startService()


Download Service

onHandleIntent()

2

3

queue intent

dequeue intent

Service Handler

sendMessage()

handleMessage()

Intent

In contrast, a Service must stop itself manually via stopSelf()


37

The IntentService

Implementation


38

Implementation of IntentService

frameworks/base/core/java/android/os/IntentService.java has the code


39

Implementation of IntentService public class IntentService extends Service { ...

Base class for Services that handle asynchronous requests (expressed as Intents) on demand


40

Implementation of IntentService public class IntentService extends Service { ...

Base class for Services that handle asynchronous requests (expressed as Intents) on demand


41

Implementation of IntentService public class IntentService extends Service { ... private volatile Looper mServiceLooper; private volatile ServiceHandler mServiceHandler; public void onCreate() { super.onCreate(); HandlerThread thread = new HandlerThread("IntentService[" + mName + "]"); thread.start(); mServiceLooper = thread.getLooper(); mServiceHandler = new ServiceHandler(mServiceLooper); }

Useful data members

The volatile keyword ensures data members are properly visible to Threads


42


Called when IntentService is first created


43


Create/start a separate HandlerThread to process the Intent concurrently in the background


44


Create/start a separate HandlerThread to process the Intent concurrently in the background

See earlier part on “Android Looper”


45

Implementation of IntentService public class IntentService extends Service { ... private volatile Looper mServiceLooper; private volatile ServiceHandler mServiceHandler; public void onCreate() { super.onCreate(); HandlerThread thread = new HandlerThread ("IntentService[" + mName + "]"); thread.start(); mServiceLooper = thread.getLooper(); mServiceHandler = new ServiceHandler(mServiceLooper); }

Get the HandlerThread's Looper & use it for our Handler


46

Implementation of IntentService public class IntentService extends Service { ... private volatile Looper mServiceLooper; private volatile ServiceHandler mServiceHandler; public void onCreate() { super.onCreate(); HandlerThread thread = new HandlerThread ("IntentService[" + mName + "]"); thread.start(); mServiceLooper = thread.getLooper(); mServiceHandler = new ServiceHandler(mServiceLooper); }

Get the HandlerThread's Looper & use it for our Handler


47

Implementation of IntentService public class IntentService extends Service { ... public int onStartCommand(Intent intent, int f, int startId) { onStart(intent, startId); return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY; } public void onStart(Intent intent, int startId) { Message msg = mServiceHandler.obtainMessage(); msg.arg1 = startId; msg.obj = intent; mServiceHandler.sendMessage(msg); } ...

Called each time a Started Service is sent an Intent via startService()


48


Helper method


49

Implementation of IntentService public class IntentService extends Service { ... public int onStartCommand(Intent intent, int f, int startId) { onStart(intent, startId); return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY; } public void onStart(Intent intent, int startId) Message msg = mServiceHandler.obtainMessage(); msg.arg1 = startId; msg.obj = intent; mServiceHandler.sendMessage(msg); } ...

Forwards Intent to the ServiceHandler


50

Implementation of IntentService public class IntentService extends Service { ... public int onStartCommand(Intent intent, int f, int startId) { onStart(intent, startId); return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY; } public void onStart(Intent intent, int startId) Message msg = mServiceHandler.obtainMessage(); msg.arg1 = startId; msg.obj = intent; mServiceHandler.sendMessage(msg); } ...

Create a Message


51


Include Intent & start ID in Message to guide subsequent processing & shutdown


52


Send Message to ServiceHandler for processing in the background Thread


53

Implementation of IntentService public class IntentService extends Service { ... private final class ServiceHandler extends Handler { public ServiceHandler(Looper looper) { super(looper); } public void handleMessage(Message msg) { onHandleIntent((Intent) msg.obj); stopSelf(msg.arg1); } } ...

Receives Messages passed via sendMessage()


54


Receives Messages passed via sendMessage()


55


Dispatch a callback hook method to process the Intent concurrently


56


Dispatch a callback hook method to process the Intent concurrently


57

Implementation of IntentService public class IntentService extends Service { ... protected abstract void onHandleIntent(Intent intent); ... Must be overridden by

subclasses to process the Intent concurrently

Only one Intent at a time is processed concurrently


58


Stop the service using the startId, so that we don't stop the service in the middle of handling another job

See previous part on “Programming Started Services”


59

Implementation of IntentService public class IntentService extends Service { ... public void onDestroy() { mServiceLooper.quit(); } }

Shutdown the looper


60

Summary


61

• IntentService provides a framework that codifies a common Android idiom

Summary

onHandleIntent()

…

process intent

Download Service

Service Handler

sendMessage()

onCreate()

onStartCommand()

Intent Intent Service

send intent

startService()

handleMessage()

Client


62

• IntentService provides a framework that codifies a common Android idiom • It creates a Handler

Thread that processes Intent commands in the background

Summary

onHandleIntent()

…

process intent

Download Service

Service Handler

sendMessage()

onCreate()

onStartCommand()


send intent

startService()

handleMessage()

Client


63



• It also uses the HaMeR framework to dispatch calls to onHandleIntent()

Summary

onHandleIntent()

…

process intent

Download Service

3

queue intent

dequeue intent

Service Handler

sendMessage()

onCreate()

onStartCommand()

2


send intent

startService()

handleMessage()

4 5

1 Client


64




Summary

onHandleIntent()

…

process intent

Download Service

3

queue intent

dequeue intent

Service Handler

sendMessage()

onCreate()

onStartCommand()

2


send intent

startService()

handleMessage()

4 5

1 Client

IntentService is designed for Services that process one Intent request at a time


65




Summary

onHandleIntent()

…

process intent

Download Service

3

queue intent

dequeue intent

Service Handler

sendMessage()

onCreate()

onStartCommand()

2


send intent

startService()

handleMessage()

4 5

1 Client

Executors can be used to process Intents concurrently in a pool of Threads


66

Summary • IntentService provides a

framework that codifies a common Android idiom • It creates a Handler


• It also uses the HaMeR framework to serialize calls to onHandleIntent()

• It applies the Command Processor pattern

Client

3

2 Queue request

See upcoming parts on “The Command Processor Pattern”


67 See previous parts on “Programming Started Services”


framework that codifies a common Android idiom • It creates a Handler


• It also uses the HaMeR framework to serialize calls to onHandleIntent()

• It applies the Command Processor pattern

• It shows how frameworks evolve organically by refactoring software

Groundhog Day


68

packages/apps/Calendar/src/com/android/calendar/alerts/ DismissAllAlarmsService.java packages/apps/CellBroadcastReceiver/src/com/android/cellbroadcastreceiver/ CellBroadcastDatabaseService.java packages/apps/Contacts/src/com/android/contacts/ContactSaveService.java packages/apps/Email/src/com/android/email/service/ EmailBroadcastProcessorService.java packages/apps/Exchange/src/com/android/exchange/service/ ExchangeBroadcastProcessorService.java packages/apps/MusicFX/src/com/android/musicfx/Compatibility.java packages/apps/Phone/src/com/android/phone/ClearMissedCallsService.java


framework that codifies a common Android idiom

• IntentService is heavily used in Android’s packaged applications


69






70





www.vogella.com/articles/AndroidServices/article.html#service_intentservices

http://www.vogella.com/articles/AndroidServices/article.html#service_intentservices

http://www.vogella.com/articles/AndroidServices/article.html#service_intentservices

S2 M1 P4 Android IntentService

Documents