Working with WorkManager

The Architecture Component for deferrable, asynchronous background work ⚙️

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By Nick Rout

Android Engineer at Over

Twitter: @ricknout

What is it ❓

• A Jetpack Architecture Component!

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• For (potentially long running) async background work

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• Deferrable: not required to run immediately
• Constrained: runs when device constraints are met
• Guaranteed: runs even if app exits / device restarts

What is it ❓

• Wraps existing frameworks, depending on device API level
• API 23+: JobScheduler
• API 14-22: BroadcastReceiver + AlarmManager

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• Works with or without Google Play Services

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• Plays nicely with (and internally makes use of) other Architecture Components eg. LiveData, Room

When should it be used 🤔

• “Fire and forget” scenarios
• Syncing local data (periodically) with network
• Sending analytics events
• Large file uploads/downloads
• Applying filters to a Bitmap and saving to storage
• A chain of all of the above

When should it be used 🤔

Source: Modern background execution in Android

Rugby Ranker 🏉

• WorkManager used to periodically sync World Rugby rankings/matches
• Work involves network (Retrofit), database (Room), SharedPreferences

Basic setup 🏁

• Latest version: 1.0.0-rc02

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• In this presentation: Kotlin (hence -ktx)

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• Gradle dependencies:

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implementation “android.arch.work:work-runtime-ktx:$work-version”

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implementation “android.arch.work:work-testing:$work-version”

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Your first Worker 🥇

• Extend the Worker class
• Override the doWork() function
• Return a Result
• Success, Retry, Failure
• Optional: output Data (Map<String, ?>)

Your first Worker 🥇

class RankingsWorker(

context: Context,

workerParams: WorkerParameters

private val rankingsRepository: RankingsRepository

) : Worker(context, workerParams) {

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override fun doWork() = fetchAndCacheLatestWorldRugbyRankings()

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private fun fetchAndCacheLatestWorldRugbyRankings(): Result {

val success = rankingsRepository

.fetchAndCacheLatestWorldRugbyRankingsSync()

return if (success) Result.success() else Result.retry()

}

}

Your first Worker 🥇

class RankingsWorker(

context: Context,

workerParams: WorkerParameters

private val rankingsRepository: RankingsRepository

) : Worker(context, workerParams) {

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override fun doWork() = fetchAndCacheLatestWorldRugbyRankings()

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private fun fetchAndCacheLatestWorldRugbyRankings(): Result {

val success = rankingsRepository

.fetchAndCacheLatestWorldRugbyRankingsSync()

return if (success) Result.success() else Result.retry()

}

}

Your first Worker 🥇

class RankingsWorker(

context: Context,

workerParams: WorkerParameters

private val rankingsRepository: RankingsRepository

) : Worker(context, workerParams) {

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override fun doWork() = fetchAndCacheLatestWorldRugbyRankings()

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private fun fetchAndCacheLatestWorldRugbyRankings(): Result {

val success = rankingsRepository

.fetchAndCacheLatestWorldRugbyRankings()

return if (success) Result.success() else Result.retry()

}

}

Define some constraints 📱

• Device must be charging
• Device must be idle
• Network connectivity type
• Battery must not be low
• Storage must not be low
• A few others that match JobScheduler

Define some constraints 📱

val constraints = Constraints.Builder()

.setRequiredNetworkType(NetworkType.CONNECTED)

.build()

Create a WorkRequest (one-time) 1️⃣

• Reference the Worker class
• Set constraints
• Optional: set input Data (Map<String, ?>)
• Optional: add tag/s
• Optional: set a backoff criteria
• EXPONENTIAL, LINEAR
• Duration

Create a WorkRequest (periodic) ⏲️

• Same as one-time request
• Adds: repeat interval (minimum 15 minutes)

Create a WorkRequest (periodic) ⏲️

val rankingsWorkRequest =

PeriodicWorkRequestBuilder<RankingsWorker>(1L, TimeUnit.Days)

.setConstraints(constraints)

.build()

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// Use OneTimeWorkRequestBuilder for one-time requests

Enqueue your work! 🎉

• Get an instance of WorkManager
• Use the WorkRequest
• Set a unique work name (an identifier of sorts)
• Choose a policy for existing work
• REPLACE, KEEP

Enqueue your work! 🎉

val workManager = WorkManager.getInstance()

val uniqueWorkName = “rankings_worker”

workManager.enqueueUniquePeriodicWork(

uniqueWorkName, ExistingPeriodicWorkPolicy.KEEP, rankingsWorkRequest

)

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// Use enqueueUniqueWork for one-time work

Monitor Worker state 👂

• Query WorkManager for enqueued work
• By unique work name or tag
• Can return multiple results because of common tags or chained work
• Returns a LiveData<WorkInfo>
• Check WorkInfo.State on change

Monitor Worker state 👂

val workManager = WorkManager.getInstance()

val uniqueWorkName = “rankings_worker”

val rankingsWorkInfoLiveData =

workManager.getWorkInfosForUniqueWorkLiveData(uniqueWorkName)

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// Use getWorkInfosByTagLiveData for tags

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rankingsWorkInfoLiveData.observe(lifecycleOwner, Observer { workInfos ->

val workInfo = workInfos?.firstOrNull() ?: return@Observer

when (workInfo.state) {

State.RUNNING -> // Show Snackbar

else -> // Hide Snackbar

})

Monitor Worker state 👂

val workManager = WorkManager.getInstance()

val uniqueWorkName = “rankings_worker”

val rankingsWorkInfoLiveData =

workManager.getWorkInfosForUniqueWorkLiveData(uniqueWorkName)

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// Use getWorkInfosByTagLiveData for tags

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rankingsWorkInfoLiveData.observe(lifecycleOwner, Observer { workInfos ->

val workInfo = workInfos?.firstOrNull() ?: return@Observer

when (workInfo.state) {

State.RUNNING -> // Show Snackbar

else -> // Hide Snackbar

})

Retrieve output data 🎁

• Uses the Data class (wrapper for Map<String, ?>)
• Remember from earlier - Result.success(outputData) returned by Worker.doWork()
• Use the same approach for worker state and LiveData<WorkInfo>
• Instead of workInfo.state - workInfo.outputData
• How long are results kept around for? Use WorkRequest.Builder.keepResultsForAtLeast

Cancel running work ❌

• Cancel work via instance of WorkManager
• By unique work name: cancelUniqueWork
• By tag: cancelAllWorkByTag
• CAUTION: cancelAllWork

Gotcha: Retrofit network calls 📡

• There is no asynchronous callback support inside a Worker
• doWork() needs to return a Result
• We can’t use Retrofit’s Callback mechanism
• So then…
• Instead of: service.call().enqueue(callback)
• Use: val response = service.call().execute()
• Handle null/errors/exceptions manually

Dependency injection with Dagger 💉

• We want to be able to inject certain classes eg. Repositories, UseCases
• WorkerFactory available for custom class instantiation, some Manifest work too
• Similar to the ViewModelFactory approach? Nope…
• Worker constructor includes WorkerParameters which Dagger doesn’t know about

Dependency injection with Dagger 💉

Let’s open up the article...

Incorporating Kotlin Coroutines ↪️

• Instead of Worker - CoroutineWorker!
• doWork() is now a suspend fun
• No need to use runBlocking
• Internally handles Coroutine context + scopeservice.call().enqueue(callback)

Incorporating Kotlin Coroutines ↪️

// Before

class RankingsWorker(

context: Context,

workerParams: WorkerParameters

private val rankingsRepository: RankingsRepository

) : Worker(context, workerParams) {

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override fun doWork() = runBlocking {

fetchAndCacheLatestWorldRugbyRankings()

}

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private suspend fun fetchAndCacheLatestWorldRugbyRankings(): Result {

val success = rankingsRepository

.fetchAndCacheLatestWorldRugbyRankings() // Now suspending

return if (success) Result.success() else Result.retry()

}

}

Incorporating Kotlin Coroutines ↪️

// After

class RankingsWorker(

context: Context,

workerParams: WorkerParameters

private val rankingsRepository: RankingsRepository

) : CoroutineWorker(context, workerParams) {

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override suspend fun doWork() = fetchAndCacheLatestWorldRugbyRankings()

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private suspend fun fetchAndCacheLatestWorldRugbyRankings(): Result {

val success = rankingsRepository

.fetchAndCacheLatestWorldRugbyRankings() // Now suspending

return if (success) Result.success() else Result.retry()

}

}

More resources 📚

• Schedule tasks with WorkManager (Android docs)
• Background Work with WorkManager (Codelab)
• Introducing WorkManager (Medium)
• Modern background execution in Android (Blog)
• Working with WorkManager (Android Dev Summit video)
• Dagger + WorkManager
• Rugby Ranker (GitHub)

Any questions? 🤷‍♂️