Kotlin’S Flow on Android App Development 

Kotlin’s Corutine Flow on Android Development Su Myat Tun GDE for Android,WTM Ambassador Senior Android Dev,Lomotif(SG) 

1. Reactive streams : common practical use case on Android Development 2. Backpressure : every software dev will have to deal with this at some point(reading & writing) 3. Kotlin’s Flow & Action : let’s get our hands dirty ;) What we’ll talk about today 

What’s Backpressure? 

“Resistance or force opposing the desired flow of data through software.” 

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Reactive streams on Android 

“The purpose of Reactive Streams is to provide a standard for asynchronous stream processing with non-blocking backpressure.” 

1. Rxjava : very powerful, many features ,steep learning curve 2. Flow : very powerful & very easy to use (Livedata, Rxjava & Flow implement the observer pattern in your code) What’re powerful tool for reactive stream? 

Kotlin’s Flow 

1. based on suspending functions 2. is an additional to kotlin coroutines 3. simplify asynchronous work by getting rid of callbacks 4. emits the value sequentially What’s Flow 

1. make a request to network 2. accessing the internal storage Most particle common use case 

1. Flow Builder 2. Flow Operator In Kotlin’s Flow 

Flow architecture UI ViewModel Repository DataSource flow flow livedata 

The most basic Flow Builder val colorsFlow = flow { val names = listOf("White", "Black", "Pink", "Blue","Red") for (name in names) { delay(100) emit(name) } } val colorsFlowOf = flowOf("White", "Black", "Pink", "Blue","Red") val colorsAsFlow = listOf("White", "Black", "Pink", "Blue","Red").asFlow() 

Flow Operator - intermediate fun main() = runBlocking { colorsFlowOf .map { name -> name.length } .filter { length -> length < 5 } println() } 

How’s map & filter work White 5 Black 5 Pink 4 4 Blue 4 4 Red 3 3 map filter 

Flow Operator - terminal fun main() = runBlocking { colorsFlowOf .map { name -> name.length } .filter { length -> length < 5 } .collect { println(it) } } 

How flow on development 

Going to the following link, and access the sample project I created in git https://github.com/suhtun/Dagger4U.git What you’ll need: 

Application architecture UI ViewModel Repository DataSource flow flow livedata 

DataSource: Remote API calls with Retrofit @GET("now_playing?page=1") suspend fun getPlayingMovie(): PlayingMoviewsResponse 

DataSource: Local data calls with Room @Query("SELECT * FROM movie_table") suspend fun getMovies(): List 

Repository override fun getMovieList(): Flow>> { return flow { emit(ViewState.loading>()) emit(ViewState.success(movieDao.getMovies())) val response =service.getPlayingMovie() response.movieResults.let { movieDao.insertMovies(it.map {Movie(...)}) } emit(ViewState.success(movieDao.getMovies())) }.catch {emit(ViewState.error(it.message.orEmpty())) }.flowOn(Dispatchers.IO) } 

ViewModel val results : LiveData>> = Transformations .switchMap(callRepo) { search -> if (search.isNullOrBlank()) { AbsentLiveData.create() } else { repository.getMovieList().asLiveData() } } 

UI viewmodel.results.observe(viewLifecycleOwner, Observer { result -> loading = true if (result.data != null) adapter.submitList(result?.data) }) 

https://codelabs.developers.google.com/c odelabs/advanced-kotlin-coroutines/#7 Keep learning: 

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