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Background Tasks

Lesson 7

Android Developer Fundamentals V2

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Services

Android Developer Fundamentals V2

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Services

Android Developer Fundamentals V2

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7.4 Services

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Services

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Contents

  • Services for long tasks.
  • IntentService

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Services

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Services is an advanced topic

  • Services are complex.
  • Many ways of configuring a service.
  • This lesson has introductory information only.
  • Explore and learn for yourself if you want to use services.

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Services

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Services for Long Tasks

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Services

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What is a service?

A Service is an application component that can perform long-running operations in the background and does not provide a user interface.

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Services

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What are services good for?

  • Network transactions.
  • Play music.
  • Perform file I/O.
  • Interact with a database.

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Services

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Characteristics of services

  • Started with an Intent.
  • Can stay running when user switches applications.
  • Lifecycle—which you must manage.
  • Other apps can use the service—manage permissions.
  • Runs in the main thread of its hosting process.

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Services

Android Developer Fundamentals V2

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Forms of services: started

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  • Started with startService()
  • Runs indefinitely until it stops itself
  • Usually does not update the UI

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Services

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Forms of services: bound

  • Offers a client-server interface that allows components to interact with the service
  • Clients send requests and get results
  • Started with bindService()
  • Ends when all clients unbind

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Services

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Services and threads

Although services are separate from the UI, they still run on the main thread by default (except IntentService)

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Offload CPU-intensive work to a separate thread within the service

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Services

Android Developer Fundamentals V2

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Updating the app

If the service can't access the UI, how do you update the app to show the results?

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Use a broadcast receiver!

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Services

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Foreground services

Runs in the background but requires that the user is actively aware it exists—e.g. music player using music service

  • Higher priority than background services since user will notice its absence—unlikely to be killed by the system
  • Must provide a notification which the user cannot dismiss while the service is running

​

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Services

Android Developer Fundamentals V2

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Background services limitations

  • Starting from API 26, background app is not allowed to create a background service.
  • A foreground app, can create and run both foreground and background services.
  • When an app goes into the background, the system stops the app's background services.
  • The startService() method now throws an IllegalStateException if an app is targeting API 26.
  • These limitations don't affect foreground services or bound services.

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Services

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Creating a service

  • <service android:name=".ExampleService" />
  • Manage permissions.
  • Subclass IntentService or Service class.
  • Implement lifecycle methods.
  • Start service from Activity.
  • Make sure service is stoppable.

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Services

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Stopping a service

  • A started service must manage its own lifecycle
  • If not stopped, will keep running and consuming resources
  • The service must stop itself by calling stopSelf()
  • Another component can stop it by calling stopService()
  • Bound service is destroyed when all clients unbound
  • IntentService is destroyed after onHandleIntent() returns

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Services

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IntentService

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Services

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IntentService

  • Simple service with simplified lifecycle
  • Uses worker threads to fulfill requests
  • Stops itself when done

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  • Ideal for one long task on a single background thread

​

​

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Services

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IntentService Limitations

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  • Cannot interact with the UI
  • Can only run one request at a time
  • Cannot be interrupted

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​

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Services

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IntentService restrictions

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  • IntentService are subjected to the new restrictions on background services.
  • For the apps targeting API 26, Android Support Library 26.0.0 introduces a new JobIntentService.
  • JobIntentService provides the same functionality as IntentService but uses jobs instead of services.

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Services

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IntentService Implementation

public class HelloIntentService extends IntentService {

public HelloIntentService() { super("HelloIntentService");}

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@Override

protected void onHandleIntent(Intent intent) {

try {

// Do some work

} catch (InterruptedException e) {

Thread.currentThread().interrupt();

}

} // When this method returns, IntentService stops the service, as appropriate.

}

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Services

Android Developer Fundamentals V2

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Learn more

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What's Next?

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  • Concept Chapter: 7.4 Services
  • No practical

Services

Android Developer Fundamentals V2

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END

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Services

Android Developer Fundamentals V2

This work is licensed under a Creative Commons Attribution 4.0 International License.