Kotlin's Flow on Android App Development

Asynchronous programming is complex. In this talk, you will learn about Kotlin's Flow where to use, and how Flow's help write reliable apps. I'll present using a sample application that will dive straight in and have a look at the basics, getting from API calls to our UI only using Kotlin's Flow with LiveData, ViewModel, and the repository pattern. After this talk, you'll see how Flows enable writing safe, reliable, and how it can strengthen your app development.

Transcript

1. Kotlin’S Flow on Android App Development
2. Kotlin’s Corutine Flow on Android Development Su Myat Tun GDE for Android,WTM Ambassador Senior Android Dev,Lomotif(SG)
3. 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
4. What’s Backpressure?
5. “Resistance or force opposing the desired flow of data through software.”
7. Reactive streams on Android
8. “The purpose of Reactive Streams is to provide a standard for asynchronous stream processing with non-blocking backpressure.”
9. 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?
10. Kotlin’s Flow
11. 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
12. 1. make a request to network 2. accessing the internal storage Most particle common use case
13. 1. Flow Builder 2. Flow Operator In Kotlin’s Flow
14. Flow architecture UI ViewModel Repository DataSource flow flow livedata
15. 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()
16. Flow Operator - intermediate fun main() = runBlocking { colorsFlowOf .map { name -> name.length } .filter { length -> length < 5 } println() }
17. How’s map & filter work White 5 Black 5 Pink 4 4 Blue 4 4 Red 3 3 map filter
18. Flow Operator - terminal fun main() = runBlocking { colorsFlowOf .map { name -> name.length } .filter { length -> length < 5 } .collect { println(it) } }
19. How flow on development
20. Going to the following link, and access the sample project I created in git https://github.com/suhtun/Dagger4U.git What you’ll need:
21. Application architecture UI ViewModel Repository DataSource flow flow livedata
22. DataSource: Remote API calls with Retrofit @GET("now_playing?page=1") suspend fun getPlayingMovie(): PlayingMoviewsResponse
23. DataSource: Local data calls with Room @Query("SELECT * FROM movie_table") suspend fun getMovies(): List<Movie>
24. Repository override fun getMovieList(): Flow<ViewState<List<Movie>>> { return flow { emit(ViewState.loading<List<Movie>>()) 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) }
25. ViewModel val results : LiveData<ViewState<List<Movie>>> = Transformations .switchMap(callRepo) { search -> if (search.isNullOrBlank()) { AbsentLiveData.create() } else { repository.getMovieList().asLiveData() } }
26. UI viewmodel.results.observe(viewLifecycleOwner, Observer { result -> loading = true if (result.data != null) adapter.submitList(result?.data) })
27. https://codelabs.developers.google.com/c odelabs/advanced-kotlin-coroutines/#7 Keep learning:
28. Question???