This session takes a deep dive into several real-world rewrites of large features in a popular app using exclusively reactive streams, from the view all the way to the network!
@pacoworks Key Takeaways Take business requirements and convert them into a reactive domain model Create your own solutions to general problems Apply those solution to specific use cases Write code for maintainability 2
@pacoworks Information breakdown Select any number of songs Play previews inline Filters by genre Do not display songs already on soundtrack 9 List of songs Set of selected songs Play information: total and currently played List of filters Currently selected filter List of soundtrack songs
@pacoworks Model 10 List of songs List of selected songs Play information: total and currently played List of filters Currently selected filter List of soundtrack songs typealias Genre = String data class Song(val genre: Genre, val url: String, ...) data class Beat(val current: Int, val total: Int) data class SoundtrackElement(val song: Song, ...)
@pacoworks State 11 Select any number of songs Play previews inline Filters by genre Do not display songs already on soundtrack val songList: BehaviorSubject> = BehaviorSubject.create(emptyList()) val songSelected: BehaviorSubject> = BehaviorSubject.create(emptySet()) val filterList: BehaviorSubject> = BehaviorSubject.create(emptyList()) val filterSelected: BehaviorSubject> = BehaviorSubject.create(emptySet()) val soundtrack: BehaviorSubject> = BehaviorSubject.create(emptyList()) Say bye bye to songs on soundtrack for now Notice there is no Beat state. Beats are transient data.
@pacoworks View display Select any number of songs Play previews inline Filters by genre 14 interface MusicViewDisplay { fun showSongs(songs: List) fun showSelected(selected: Set) fun showBeat(beat: Tuple2) fun clearBeat() fun showGenres(genres: List) fun showVisible(visible: Set) }
@pacoworks Binding State to UI fun bind(lifecycle: Observable, mainThreadScheduler: Scheduler, state: Observable, viewAction: (T) -> Unit) = lifecycle .filter(is(CREATE)) .switchMap(state) .observeOn(mainThreadScheduler) .takeUntil( lifecycle .filter(is(DESTROY))) .subscribe(viewAction) 15 No leaky UI! Bind with lifecycle assurance Add main thread too Observable subscribed with (T) -> Unit
@pacoworks View display Select any number of songs Play previews inline Filters by genre 16 val bindSimple = ::bind.apply( lifecycle, AndroidSchedulers.mainThread()) bindSimple(songList, ::showSongs) bindSimple(songSelected, ::showSelected) bindSimple(filterList, ::showGenres) bindSimple(filterSelected, ::showVisible) Beats have no permanent state -> no binding!
@pacoworks View adapter Select any number of songs Play previews inline Filters by genre 17 class MusicAdapter: RecyclerView.Adapter { val songs: List val selected: Set val visible: Set val beat: AtomicReference> /*...*/ } class MusicFilterSpinner: BaseAdapter { val genres: List /*...*/ }
@pacoworks View adapter Select any number of songs Play previews inline Filters by genre 18 class MusicAdapter: RecyclerView.Adapter { val selected: Set val visible: Set val beat: AtomicReference> fun getItemViewType(pos: Int, element: Song): Int = if visible.contains(element) SHOW else HIDDEN fun onCreateViewHolder(parent: ViewGroup, viewType: Int): VH = if (viewType == HIDDEN) HiddenSongViewHolder(parent.context) else SongViewHolder(/*...*/) fun onBindViewHolder(holder: VH, pos: Int) { val position = songs.get(pos); if (selected.contains(position)) { /*...*/ } val beatC = beat.get() if (beatC != null && beatC.b == position) { /*...*/ } } }
@pacoworks Information sources Select any number of songs Play previews inline Filters by genre 21 Song Provider: network Media Player: Android Framework Filters: derived from list of songs
@pacoworks Song Provider Select any number of songs Play previews inline Filters by genre Do not display songs already on soundtrack 22 interface SongService { fun getListOfSongs(): Observable> } interface SongAPI { fun getSongs(): Observable> } object SongProvider: SongService { override fun getListOfSongs(): Observable> = /*...*/ }
@pacoworks Song Provider Select any number of songs Play previews inline Filters by genre Do not display songs already on soundtrack 23 object SongProvider: SongService { override fun getListOfSongs(): Observable> = getAPI().getSongs() // Failure policy .retry(3) .flatMap { songPOJOs -> toSongList(songPOJOs) } .flatMap { songs -> getSoundtrack().flatMap { soundtrack -> Observable.from(songs).filter { song -> !soundtrack.contains(song) } } } .toList() // Error handling with a good default .onErrorReturn(emptyList()) }
@pacoworks Media Player Select any number of songs Play previews inline Filters by genre 24 data class AndroidMusicPlayer(url: String) { fun play(): Observable = /* ... */ fun observeBeats(): Observable = /* ... */ fun stop(): Observable = /* ... */ } interface SongPlayer { fun playSong(url: String): Observable } data class Player(val lfcy: Observable): SongPlayer { override fun playSong(url: String): Observable = AndroidMusicPlayer(url).let { player -> player.play() .flatMap { player.observeBeats() } .takeUntil(lfcy.filter { it is PAUSE }) .concatWith(player.stop()) } }
@pacoworks Media Player Select any number of songs Play previews inline Filters by genre 25 data class AndroidMusicPlayer private constructor (url: String) { fun play(): Observable = /* ... */ fun observeBeats(): Observable = /* ... */ fun stop(): Observable = /* ... */ companion object { operator fun invoke(url: String) = Observable.create { /* url validation code */ } } } data class Player(val lfcy: Observable): SongPlayer { override fun playSong(url: String): Observable = AndroidMusicPlayer(url).flatMap { player -> player.play() .flatMap { player.observeBeats() } .takeUntil(lfcy.filter { it is PAUSE }) .concatWith(player.stop()) } }
@pacoworks User Interaction Select any number of songs Play previews inline Filters by genre 26 interface UserInteractionProvider { fun clickSong(): Observable> fun clickPlay(): Observable> fun clickStop(): Observable> fun clickFilter(): Observable fun clickSave(): Observable } Two separate buttons for play/stop
@pacoworks Breaking down use cases Match data sources with resulting state Work on small, self-contained ideas Use cases talk between them by modifying state State gets applied to UI automatically 28
@pacoworks Saving to soundtrack - with syntactic sugar 35 // Service fun clickSave() : Observable // State val songSelected : BehaviorSubject> val soundtrack : BehaviorSubject> ObservableKW.monadErrorSwitch().binding { val selectedSongs = songSelected.bind().toList() clickSave().bind() val currentSoundtrack = soundtrack.bind() currentSoundtrack + selectedSongs }.fix().subscribe(soundtrack)
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