a semantic approach to english grammar 2nd edition

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: Programming Started Services

(Part 1)

Android Services & Security: Programming Started Services (Part 1)

2

Learning Objectives in this Part of the Module Understand how to program a Started Service

e.g., a Download Application that uses a Started Service to retrieve & display an image from a remote server

Download Service

Download Activity

Socket

Socket

Send HTTP GET request


3

Download Application Overview


4

1. DownloadActivity uses startService() to launch a DownloadService


Download Activity


5



Download Activity


6



Download Service

Download Activity

startService()


7



Download Service

Download Activity

startService()


8

1. DownloadActivity uses startService() to launch a DownloadService 2. The DownloadService retrieves the image & stores it in a file on the device


Download Service

Download Activity


9

1. DownloadActivity uses startService() to launch a DownloadService 2. The DownloadService retrieves the image & stores it in a file on the device


Download Service

Download Activity

Socket

Socket



10

1. DownloadActivity uses startService() to launch a DownloadService 2. The DownloadService retrieves the image & stores it in a file on the device 3. The DownloadService returns the pathname of the file back to the

DownloadActivity, which then displays the image


Download Service

Download Activity

Send reply


11




Download Service

Download Activity

Send reply

Well just cover steps 1 & 2 in this part


12




Download Service

Download Activity

Send reply

See upcoming parts on Activity & Service Communication


13 github.com/douglascraigschmidt/POSA-14/tree/master/ex/DownloadApplication

Tips to Understand the Download Application Run/read the code & watch the video carefully to understand how it works


14

Tips to Understand the Download Application Run/read the code & watch the video carefully to understand how it works This example is complex since many classes & Android mechanisms are used


15

Tips to Understand the Download Application Run/read the code & watch the video carefully to understand how it works This example is complex since many classes & Android mechanisms are used

We therefore analyze it from various perspectives


16

Programming Started Services

(Part 1)


17

Programming a Started Service

Download Service

Socket

Socket


Download Activity


18

Launching a Started Service A client launches a Started Service by calling startService()

Intent intent = DownloadService.makeIntent (this, Uri.parse(url), downloadHandler); startService(intent);

Download Activity

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


19


e.g., Download Activity creates an Intent that identifies the DownloadService & supplies a URL parameter via Intent data that tells Service what image to retrieve

Download Activity



20



Download Activity



21



Download Activity


This call doesnt block the client while the

DownloadService runs


22

Processing a Started Service In response to startService(), Android will launch the

Service if its not already running

Download Service

Download Activity

Androids Activity Manager launches the DownloadService

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


23


Service if its not already running Android then invokes the Services onCreate() &

onStartCommand() hook methods

Download Service

Download Activity

public class DownloadService extends Service { public void onCreate() { ... } public int onStartCommand(Intent intent, int flags, int startId) { ... } ...


24




Download Service

Download Activity

public class DownloadService extends Service { public void onCreate() { ... } public int onStartCommand(Intent intent, int flags, int startId) { ... } ...


25




public class DownloadService extends Service { public void onCreate() { ... }

Download Service

Download Activity

onCreate() starts a HandlerThread


26




public class DownloadService extends Service { public void onCreate() { ... }

Download Service

Download Activity

HandlerThread works with a ServiceHandler to download the image in the background & return pathname to client


27

Programming Started Services

(Part 2)


28




public class DownloadService extends Service { public int onStartCommand(Intent intent, int flags, int startId) { ... }

Download Service

Download Activity

onStartCommand() sends the Intent to the background HandlerThread


29




Download Service

Download Activity

public class DownloadService extends Service { public int onStartCommand(Intent intent, int flags, int startId) { return ...; }

onStartCommand() returns a result to Android, but not to the client


30

Processing a Started Service After a client calls startService() Android invokes the

Services onCreate() & onStartCommand() hook methods If Service not already running, it will be started & will

receive the Intent via onStartCommand() onStartCommand() returns a result to Android, but not

to the client

Download Service

Download Activity


Return value tells Android what it should do with the Service if its process is killed while it is running


31




to the client

Download Service

Download Activity


Return value tells Android what it should do with the Service if its process is killed while it is running START_STICKY Dont redeliver Intent to onStartCommand() (pass null intent)


32




to the client

Download Service

Download Activity


Return value tells Android what it should do with the Service if its process is killed while it is running START_STICKY Dont redeliver Intent to onStartCommand() (pass null intent) START_NOT_STICKY Service should remain stopped until explicitly started by

some client code


33




to the client

Download Service

Download Activity


Return value tells Android what it should do with the Service if its process is killed while it is running START_STICKY Dont redeliver Intent to onStartCommand() (pass null intent) START_NOT_STICKY Service should remain stopped until explicitly started by

some client code START_REDELIVER_INTENT Restart Service via onStartCommand(), supplying the

same Intent as was delivered this time


34




Download Service

Download Activity


android-developers.blogspot.com.au/2010/02/service-api-changes-starting-with.html


35

In response to startService(), Android will launch the Service if its not already running

Android then invokes the Services onCreate() & onStartCommand() hook methods

A started service typically performs a single operation & often doesnt return a result to the client

Processing a Started Service

Download Service

Download Activity

public class DownloadService extends Service { ... public void handleMessage(Message msg) { downloadImage((Intent) msg.obj); ...


36

In response to startService(), Android will launch the Service if its not already running

Android then invokes the Services onCreate() & onStartCommand() hook methods

A started service typically performs a single operation & often doesnt return a result to the client

Processing a Started Service

Download Service

Download Activity

public class DownloadService extends Service { ... public void handleMessage(Message msg) { downloadImageAndReply((Intent) msg.obj); ...

Retrieves an image from remote server & returns

pathname to client


37

When the operation is done, the Service can be stopped

Stopping a Started Service

Download Service

Download Activity

public class DownloadService extends Service { ... public void handleMessage(Message msg) { ... stopSelf(msg.arg1);


38

When the operation is done, the Service can be stopped e.g., the DownloadService call stopSelf() to shut itself

down when its done retrieving & processing an image


Download Service

Download Activity

public class DownloadService extends Service { ... public void handleMessage(Message msg) { ... stopSelf(msg.arg1);

A Service that stops itself must be careful there arent concurrent operations processing other Intents!


39

When the operation is done, the Service can be stopped e.g., the DownloadService call stopSelf() to shut itself

down when its done Conversely, a Service can be shut down if stopService()

is called by another component


Download Service

Download Activity

public class DownloadActivity ... { ... stopService(intent); ...


40

Design of the Download Application


41



42



43



44

1 send intent

Design of the Download Application DownloadActivity sends an Intent

via a call to startService() Download

Activity

Intent

startService()


45

1 send intent


via a call to startService() The DownloadService is

launched on-demand Based on the Activator pattern

Intent

onCreate()

onStartCommand()

Download Service

startService()

Download Activity 2


46

1



launched on-demand DownloadService performs

four main actions

Intent

onCreate()

onStartCommand()

Download Service

send intent startService()

Download Activity 2


47

1




four main actions 1. Creates a ServiceHandler

Associated with a single HandlerThread

Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

Create a worker

thread & Handler

3

2

sendMessage()

handleMessage()

downloadImageAndReply()


48

1






Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

Create a worker

thread & Handler

3

2

sendMessage()

handleMessage()



49

1






Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

Create a worker

thread & Handler

3

2

sendMessage()

handleMessage()



50

1






Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

Create a worker

thread & Handler

3

2

sendMessage()

handleMessage()



51

1

See earlier part on Sending & Handling Messages with Android Handler






Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

Create a worker

thread & Handler

3

2

sendMessage()

handleMessage()



52

1




four main actions 1. Creates a ServiceHandler 2. Receives & queues an Intent

in the ServiceHandler

Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2

sendMessage()

handleMessage()



53

1





in the ServiceHandler

Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2

sendMessage()

handleMessage()



54

1





in the ServiceHandler 3. ServiceHandler processes

Intent in the background Downloads image designated

by the URL in the Intent

Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2

sendMessage()

handleMessage()


Dequeue Intent

& get file

5


55

1








Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2

sendMessage()

handleMessage()


Dequeue Intent

& get file

5


56

1








Intent

onCreate()

onStartCommand()

Download Service


Download Activity

Service Handler

4 3

2

See upcoming parts on Activity & Service Communication

sendMessage()

handleMessage()


Dequeue Intent

& get file

5


57

1






Intent in the background 4. Stops itself when there are

no more Intents to handle

Intent

onCreate()

Download Service


Download Activity

Service Handler

4 3

sendMessage()

handleMessage()

Dequeue Intent

& get file

5 downloadImageAndReply()


58




four main actions This design is guided by the

Command Processor pattern

www.dre.vanderbilt.edu/~schmidt/PDF/CommandRevisited.pdf has more info

Client

3

2 Queue request


59




four main actions This design is guided by the

Command Processor pattern Offload tasks from applications

main Thread to a single backgroundThread

This pattern works if a Service neednt handle multiple requests concurrently

Client

3

2 Queue request


60

Summary


61

The Download Application uses a Started Service to retrieve & display an image from a remote server

Summary

Download Service

Socket

Socket


Download Activity


62


When a Started Service is launched, it has a lifecycle that's independent of the component that started it

Download Service

Download Activity

Summary


63


When a Started Service is launched, it has a lifecycle that's independent of the component that started it A Service can run in the background

indefinitely, even if the component that started it is destroyed

Download Service

Download Activity

Summary


64



Started Services are driven by inversion of control

Summary


65




Summary


66




The Download Application implementation is guided by a common Android idiom for concurrent Service processing

Summary

Intent

onCreate()

onStartCommand()

Download Service


Service Handler

dequeue Intent & download file

4 3

2 1 Download

Activity

sendMessage()

downloadImageAndReply() 5

handleMessage()


67




The Download Application implementation is guided by a common Android idiom for concurrent Service processing This idiom is based on the

Command Processor pattern

Summary

onHandleIntent()

process intent

Download Service

3

queue intent

dequeue intent

Service Handler

sendMessage()

onCreate()

onStartCommand()

2

Intent Service

startService()

handleMessage()

4 5

Client Activity

Intent

send intent

1

See upcoming parts on The Command Processor Pattern

Slide Number 1Learning Objectives in this Part of the ModuleDownload Application OverviewDownload Application OverviewDownload Application OverviewDownload Application OverviewDownload Application OverviewDownload Application OverviewDownload Application OverviewDownload Application OverviewDownload Application OverviewDownload Application OverviewTips to Understand the Download ApplicationTips to Understand the Download ApplicationTips to Understand the Download ApplicationProgrammingStarted Services (Part 1)Programming a Started ServiceLaunching a Started ServiceLaunching a Started ServiceLaunching a Started ServiceLaunching a Started ServiceProcessing a Started ServiceProcessing a Started ServiceProcessing a Started ServiceProcessing a Started ServiceProcessing a Started ServiceProgrammingStarted Services (Part 2)Processing a Started ServiceProcessing a Started ServiceProcessing a Started ServiceProcessing a Started ServiceProcessing a Started ServiceProcessing a Started ServiceProcessing a Started ServiceProcessing a Started ServiceProcessing a Started ServiceStopping a Started ServiceStopping a Started ServiceStopping a Started ServiceDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationDesign of the Download ApplicationSlide Number 60SummarySummarySummarySummarySummarySummarySummary

a semantic approach to english grammar 2nd edition

Documents

usa android services

started service

image stores

learning objectives