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Jossi Wolf @jossiwolf From LiveData to Coroutines Flow

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@jossiwolf @jossiwolf

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@jossiwolf Live Data, LiveData everywhere

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@jossiwolf ªġƛŸƦŊƴŸƞǛ ßŊġǕwŸĚġŢ mŊǔġ(öƴö ÇXmöǛġƞ XŭǔŸŞġƦ mŊǔġ(öƴö XŭǔŸŞġƦ

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@jossiwolf ”LiveData is an observable data holder class” - Android Developers Documentation

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@jossiwolf class HomeViewModel { val latestData: LiveData = MutableLiveData() } LiveData - an example

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@jossiwolf class HomeViewModel { val latestData: LiveData = MutableLiveData() fun refresh() { val data = fetchData() latestData.post(data) } } LiveData - an example

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@jossiwolf class HomeFragment: Fragment() { fun setupUI() { latestData.observe(viewLifecycleOwner) { data #-> ##... } } } LiveData - an example

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@jossiwolf # LiveData is great! *when used properly

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@jossiwolf # LiveData & Execution Context

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@jossiwolf class SupermarketRepository { fun fetchOpeningHours( id: SupermarketId ): LiveData = ##... } Our Repository

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@jossiwolf class SupermarketRepository { fun fetchOpeningHours( id: SupermarketId ): LiveData = ##... } Our Repository

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@jossiwolf class HelpViewModel( private val supermarketRepo: SupermarketRepository ): ViewModel() { fun fetchSupermarketOpeningHours(id: SupermarketId) = supermarketRepo.fetchOpeningHours(id).map { openingHours #-> openingHours.hours.filter { it #!= null } } } Our ViewModel

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@jossiwolf class HelpViewModel( private val supermarketRepo: SupermarketRepository ): ViewModel() { fun fetchSupermarketOpeningHours(id: SupermarketId) = supermarketRepo.fetchOpeningHours(id).map { openingHours #-> openingHours.hours.filter { it #!= null } } } Our ViewModel

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@jossiwolf class HelpViewModel( private val supermarketRepo: SupermarketRepository ): ViewModel() { fun fetchSupermarketOpeningHours(id: SupermarketId) = supermarketRepo.fetchOpeningHours(id).map { openingHours #-> openingHours.hours.filter { it #!= null } } } Our ViewModel

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@jossiwolf class HelpViewModel( private val supermarketRepo: SupermarketRepository ): ViewModel() { fun fetchSupermarketOpeningHours(id: SupermarketId) = supermarketRepo.fetchOpeningHours(id).map { openingHours #-> openingHours.hours.filter { it #!= null } } }

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@jossiwolf class HelpViewModel( private val supermarketRepo: SupermarketRepository ): ViewModel() { fun fetchSupermarketOpeningHours(id: SupermarketId) = supermarketRepo.fetchOpeningHours(id).map { openingHours #-> openingHours.hours.filter { it #!= null } } }

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@jossiwolf class HelpViewModel( private val supermarketRepo: SupermarketRepository ): ViewModel() { fun fetchSupermarketOpeningHours(id: SupermarketId) = supermarketRepo.fetchOpeningHours(id).map { openingHours #-> openingHours.hours.filter { it #!= null } } }

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@jossiwolf LiveData map( LiveData source, Function mapFunction ) { MediatorLiveData result = new MediatorLiveData#<>(); result.addSource(source, (x) #-> { result.setValue(mapFunction.apply(x)); }); return result; } cs.android.com/androidx/platform/frameworks/support/+/androidx-master-dev:lifecycle/lifecycle-livedata/src/main/java/androidx/lifecycle/Transformations.java androidx.lifecycle.Transformations#map

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@jossiwolf LiveData map( LiveData source, Function mapFunction ) { MediatorLiveData result = new MediatorLiveData#<>(); result.addSource(source, (x) #-> { result.setValue(mapFunction.apply(x)); }); return result; } cs.android.com/androidx/platform/frameworks/support/+/androidx-master-dev:lifecycle/lifecycle-livedata/src/main/java/androidx/lifecycle/Transformations.java androidx.lifecycle.Transformations#map

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@jossiwolf LiveData map( LiveData source, Function mapFunction ) { MediatorLiveData result = new MediatorLiveData#<>(); result.addSource(source, (x) #-> { result.setValue(mapFunction.apply(x)); }); return result; } cs.android.com/androidx/platform/frameworks/support/+/androidx-master-dev:lifecycle/lifecycle-livedata/src/main/java/androidx/lifecycle/Transformations.java androidx.lifecycle.Transformations#map

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@jossiwolf LiveData map( LiveData source, Function mapFunction ) { MediatorLiveData result = new MediatorLiveData#<>(); result.addSource(source, (x) #-> { result.setValue(mapFunction.apply(x)); }); return result; } cs.android.com/androidx/platform/frameworks/support/+/androidx-master-dev:lifecycle/lifecycle-livedata/src/main/java/androidx/lifecycle/Transformations.java androidx.lifecycle.Transformations#map

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@jossiwolf LiveData map( LiveData source, Function mapFunction ) { MediatorLiveData result = new MediatorLiveData#<>(); result.addSource(source, (x) #-> { result.setValue(mapFunction.apply(x)); }); return result; } cs.android.com/androidx/platform/frameworks/support/+/androidx-master-dev:lifecycle/lifecycle-livedata/src/main/java/androidx/lifecycle/Transformations.java androidx.lifecycle.Transformations#map

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@jossiwolf ”The events are dispatched on the main thread.” - Android Developers Documentation

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@jossiwolf # LiveData Observers are always called on the main thread

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@jossiwolf # It’s easy to let things slide when using LiveData

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@jossiwolf Replace LiveData Make sure threading is done properly

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@jossiwolf Replace LiveData @jossiwolf

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@jossiwolf One-Shot Streams of Data

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@jossiwolf Coroutines! One-Shot Streams of Data

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@jossiwolf Coroutines! Flow One-Shot Streams of Data

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@jossiwolf # Converting to Coroutines

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@jossiwolf fun fetchOpeningHours(id: SupermarketId): LiveData { val liveData = MutableLiveData() val openingHours = poiService.downloadOpeningHours(poiType = SUPERMARKET, id).enqueue( object: Callback() { override fun onResponse(call: Call, response: Response) { liveData.postValue(response.body()) } ##... } ) liveData.postValue(openingHours) return liveData } Repository with LiveData + Callbacks

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@jossiwolf suspend fun fetchOpeningHours(id: SupermarketId): LiveData { val liveData = MutableLiveData() val openingHours = poiService.downloadOpeningHours(poiType = SUPERMARKET, id) liveData.postValue(openingHours) return liveData } Repository with LiveData + Coroutines

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@jossiwolf suspend fun fetchOpeningHours(id: SupermarketId) = poiService.downloadOpeningHours(poiType = SUPERMARKET, id) That method as Coroutine…

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@jossiwolf With Migration Helper suspend fun fetchOpeningHours(id: SupermarketId) = poiService.downloadOpeningHours(poiType = SUPERMARKET, id) @Deprecated fun fetchOpeningHoursAsLiveData(id: SupermarketId) = liveData { emit(fetchOpeningHours(id)) }

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@jossiwolf With Migration Helper suspend fun fetchOpeningHours(id: SupermarketId) = poiService.downloadOpeningHours(poiType = SUPERMARKET, id) @Deprecated fun fetchOpeningHoursAsLiveData(id: SupermarketId) = liveData { emit(fetchOpeningHours(id)) }

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@jossiwolf With Migration Helper suspend fun fetchOpeningHours(id: SupermarketId) = poiService.downloadOpeningHours(poiType = SUPERMARKET, id) @Deprecated fun fetchOpeningHoursAsLiveData(id: SupermarketId) = liveData { emit(fetchOpeningHours(id)) }

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@jossiwolf With Migration Helper suspend fun fetchOpeningHours(id: SupermarketId) = poiService.downloadOpeningHours(poiType = SUPERMARKET, id) @Deprecated fun fetchOpeningHoursAsLiveData(id: SupermarketId) = liveData { emit(fetchOpeningHours(id)) }

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@jossiwolf With Migration Helper suspend fun fetchOpeningHours(id: SupermarketId) = poiService.downloadOpeningHours(poiType = SUPERMARKET, id) @Deprecated fun fetchOpeningHoursAsLiveData(id: SupermarketId) = liveData(context = Dispatchers.IO) { emit(fetchOpeningHours(id)) }

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@jossiwolf class HelpViewModel( private val repo: SupermarketRepository ): ViewModel() { fun fetchSupermarketOpeningHours(id: SupermarketId) = repo.fetchOpeningHours(id).map { openingHours #-> openingHours.hours.filter { it #!= null } } } Our ViewModel

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@jossiwolf class HelpViewModel( private val repo: SupermarketRepository ): ViewModel() { fun fetchSupermarketOpeningHours(id: SupermarketId) = repo.fetchOpeningHoursAsLiveData(id).map { openingHours #-> openingHours.hours.filter { it #!= null } } } Our ViewModel

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@jossiwolf class HelpViewModel( private val repo: SupermarketRepository ): ViewModel() { fun fetchSupermarketOpeningHours(id: SupermarketId) = repo.fetchOpeningHoursAsLiveData(id).map { openingHours #-> openingHours.hours.filter { it #!= null } } } Our ViewModel

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@jossiwolf Our ViewModel class HelpViewModel( private val repo: SupermarketRepository ): ViewModel() { fun fetchSupermarketOpeningHours(id: SupermarketId) = repo.fetchOpeningHoursAsLiveData(id).map { openingHours #-> openingHours.hours.filter { it #!= null } } }

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@jossiwolf Repository with Migration Helper suspend fun fetchOpeningHours(id: SupermarketId) = poiService.downloadOpeningHours(poiType = SUPERMARKET, id) @Deprecated fun fetchOpeningHoursAsLiveData(id: SupermarketId) = liveData(context = Dispatchers.IO) { emit(fetchOpeningHours(id)) }

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@jossiwolf Our ViewModel class HelpViewModel( private val repo: SupermarketRepository ): ViewModel() { fun fetchSupermarketOpeningHours(id: SupermarketId) = repo.fetchOpeningHoursAsLiveData(id).map { openingHours #-> openingHours.hours.filter { it #!= null } } }

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@jossiwolf Our ViewModel class HelpViewModel( private val repo: SupermarketRepository ): ViewModel() { fun fetchSupermarketOpeningHours(id: SupermarketId) = liveData(context = Dispatchers.IO) { val openingHours = repo.fetchOpeningHours(id) val filteredHours = openingHours.hours.filter { it #!= null } emit(filteredHours) } }

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@jossiwolf # Converting to Flow

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@jossiwolf suspend fun fetchSupermarketDetails( id: SupermarketId ): LiveData { val liveData = MutableLiveData() val cachedDetails = detailsCache[id] if (cachedDetails #!= null) liveData.postValue(cachedDetails) val freshDetails = poiService.downloadDetails(SUPERMARKET, id) liveData.postValue(freshDetails) return liveData } With LiveData

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@jossiwolf suspend fun fetchSupermarketDetails( id: SupermarketId ): LiveData { val liveData = MutableLiveData() val cachedDetails = detailsCache[id] if (cachedDetails #!= null) liveData.postValue(cachedDetails) val freshDetails = poiService.downloadDetails(SUPERMARKET, id) liveData.postValue(freshDetails) return liveData } With LiveData

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@jossiwolf suspend fun fetchSupermarketDetails( id: SupermarketId ): LiveData { val liveData = MutableLiveData() val cachedDetails = detailsCache[id] if (cachedDetails #!= null) liveData.postValue(cachedDetails) val freshDetails = poiService.downloadDetails(SUPERMARKET, id) liveData.postValue(freshDetails) return liveData } With LiveData

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@jossiwolf fun fetchSupermarketDetails( id: SupermarketId ): Flow = flow { val cachedDetails = detailsCache[id] if (cachedDetails #!= null) emit(cachedDetails) val freshDetails = poiService.downloadDetails(SUPERMARKET, id) emit(freshDetails) } With Flow

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@jossiwolf fun fetchSupermarketDetails( id: SupermarketId ): Flow = flow { val cachedDetails = detailsCache[id] if (cachedDetails #!= null) emit(cachedDetails) val freshDetails = poiService.downloadDetails(SUPERMARKET, id) emit(freshDetails) } With Flow

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@jossiwolf fun fetchSupermarketDetails( id: SupermarketId ): Flow = flow { val cachedDetails = detailsCache[id] if (cachedDetails #!= null) emit(cachedDetails) val freshDetails = poiService.downloadDetails(SUPERMARKET, id) emit(freshDetails) } With Flow

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@jossiwolf fun fetchSupermarketDetails( id: SupermarketId ): Flow = flow { val cachedDetails = detailsCache[id] if (cachedDetails #!= null) emit(cachedDetails) val freshDetails = poiService.downloadDetails(SUPERMARKET, id) emit(freshDetails) } With Flow

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@jossiwolf With Flow + Migration Helper fun fetchSupermarketDetails( id: SupermarketId ): Flow = flow { … } @Deprecated("Please use Flows directly.") fun fetchSupermarketDetailsAsLiveData( id: SupermarketId ): LiveData = fetchSupermarketDetails(id).asLiveData()

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@jossiwolf With Flow + Migration Helper fun fetchSupermarketDetails( id: SupermarketId ): Flow = flow { … } @Deprecated("Please use Flows directly.") fun fetchSupermarketDetailsAsLiveData( id: SupermarketId ): LiveData = fetchSupermarketDetails(id).asLiveData(Dispatchers.IO)

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@jossiwolf With Flow + Migration Helper fun fetchSupermarketDetails( id: SupermarketId ): Flow = flow { … } @Deprecated("Please use Flows directly.") fun fetchSupermarketDetailsAsLiveData( id: SupermarketId ): LiveData = fetchSupermarketDetails(id).asLiveData(Dispatchers.IO)

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@jossiwolf With Flow + Migration Helper fun fetchSupermarketDetails( id: SupermarketId ): Flow = flow { … } @Deprecated("Please use Flows directly.") fun fetchSupermarketDetailsAsLiveData( id: SupermarketId ): LiveData = fetchSupermarketDetails(id).asLiveData(Dispatchers.IO)

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@jossiwolf - developer.android.com/topic/libraries/architecture/livedata - proandroiddev.com/dont-use-livedata-in- repositories-f3bebe502ed3 - medium.com/@elizarov/execution-context-of-kotlin-flows-b8c151c9309b Resources

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@jossiwolf

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Jossi Wolf @jossiwolf From LiveData to Coroutines Flow