Reactive Clean Architecture

Talk on how to think when building Android apps using a reactive Clean Architecture. This talk was held at the Stockholm Android Meetup group April 17 2018 at Developers bay.

Transcript

1. Reactive Clean Architecture Viktor Nyblom @qw4z1
2. MVP MVC MVVM What isn’t Architecture X X X
3. Why clean architecture?
4. Architecture is about Intent - Uncle Bob
5. Showing intent
6. Showing intent
7. Key points ! Use Cases ! Dependencies ! Models ! Reactive ! Testable ! Independent of frameworks
8. What is a Use Case? ! Captures application business rules ! Independent of framework ! Shows WHAT the application does, not HOW X Interactor
9. Layered architecture Interactors Repositories UI DB HTTP Presenters Dependencies
10. Layered architecture Use Cases Repositories UI DB HTTP Presenters Data Domain Presentation
11. Three Layers Data Presentation Domain Model Presenter View Interactor Model Operation API Repository Cache DB Abstraction
12. Presentation data flow View Presenter D O M A I N User interaction onRefresh() execute() domainData format() showData(data) Get
 Feed
 Interactor fun getFeed(): Single<List<Tweets>>
13. What if we could observe a stream of data forever and react to new versions of that data?
14. Presentation data flow View Presenter D O M A I N User interaction onRefresh() execute() domainData format() updateData(data) Refresh
 Feed
 Interactor Observe
 Feed
 Interactor Create
 Tweet
 Interactor execute() onCreateTweet()
15. interface TweetFeedContract.Presenter
 : BasePresenter<TweetFeedContract.View> { fun onRefresh() ... } Presentation
16. interface TweetFeedContract.View
 : BaseView { fun updateFeed(list: List<DisplayableTweet>) fun showEmpty() fun showLoading() .... } Presentation
17. class TweetFeedPresenter @Inject constructor(
 private val refreshFeedInteractor: RefreshFeedInteractor,
 private val observeFeedInteractor: ObserveFeedInteractor,
 private val mapToDisplayableItem: Mapper<DisplayableItem>
 ) : TweetFeedContract.Presenter { private val disposables: CompositeDisposable
 ... } Presentation
18. override fun onRefresh() {
 refreshFeedInteractor.excecute()
 } TweetFeedPresenter
19. override fun onAttach(view: TweetFeedContract.View) {
 this.view = view
 disposables += bindToFeed()
 } TweetFeedPresenter
20. override fun bindToFeed(): Disposable =
 observeFeedInteractor
 .excecute()
 .onSubscribe { view?.showLoading() }
 .map(mapToDisplayableItem)
 .subscribe( 
 { tweets -> 
 if (tweets.notEmpty())
 view?.updateFeed(tweets)
 else
 view?.showEmpty()
 },
 { throwable -> loge(throwable) } )
 TweetFeedPresenter
21. Models should make sense in the context where they are being used.
22. What the map? public class Item { private String validTo;
 private float price; private String validFrom; private int type; }
23. What the map? public class Item { @SerializedName ("validto") private String validTo; @SerializedName ("price")
 private float price; @SerializedName ("validfrom") private String validFrom; @SerializedName (value = "type") private int type; }
24. What the map? @DatabaseTable (name = “item")
 public class Item { @DatabaseField (generatedId = true) private int _id; @DatabaseField @SerializedName ("validto") private String validTo; @DatabaseField (canBeNull = false) @SerializedName ("price")
 private float price; @DatabaseField (canBeNull = false) @SerializedName ("validfrom") private String validFrom; @DatabaseField @SerializedName (value = "type") private int type; }
25. What the map? public class APIItem { private int validto;
 private float price; private int validfrom; private int type; } @DatabaseTable (name = “item")
 public class DatabaseItem { @DatabaseField (generatedId = true) private int _id;
 @DatabaseField private int validTo;
 @DatabaseField
 private float price; @DatabaseField
 private int validFrom; @DatabaseField
 private int type; @DatabaseField
 private boolean dirty; }
26. What the map? @DatabaseTable (name = “item")
 public class DatabaseItem { @DatabaseField (generatedId = true) private int _id;
 @DatabaseField private int validTo;
 @DatabaseField
 private float price; @DatabaseField
 private int validFrom; @DatabaseField
 private int type; @DatabaseField
 private boolean dirty; } 
 public class DisplayableItem { private int _id; private DateTime validTo; private String formattedTo;
 private String formattedPrice;
 private DateTime validFrom;
 private String formattedFrom;
 private ItemType type;
 private boolean selected; }
27. What the map Data Presentation Domain Model Presenter View Interactor Model Operation API Repository Cache DB Abstraction
28. What the map Data Presentation Domain Presentation
 Model Presenter View Interactor Domain
 Model Operation API Repository Cache DB Abstraction API
 Model Cache
 Model
29. Domain data flow D A T A execute() domainData domainData Refresh
 Feed
 Interactor Abstraction
 : Tweet Repository P R E S E N TA T
 I
 O N Observe
 Feed
 Interactor onComplete() retrieveFeed() Abstraction
 : TweetList
 Repository onNext()
30. Interactors abstract class CompletableInteractor<in Params>( private val executionScheduler: Scheduler, private val postExecutionScheduler: Scheduler) { abstract fun buildInteractorCompletable(params: Params): Completable fun execute(params: Params): Completable = buildInteractorObservable(params) .subscribeOn(executionScheduler) .observeOn(postExecutionScheduler) .subscribe() }
31. Interactors class RefreshFeedInteractor @Inject constructor( private val tweetRepository: TweetRepository, executionScheduler: Scheduler, postExecutionScheduler: Scheduler) : CompletableInteractor<FeedSpec>(executionScheduler, postExecutionScheduler) { override fun buildInteractorCompletable(params: FeedSpec): Completable = tweetRepository.refreshFeed(params) }
32. Interactors abstract class ObservableInteractor<T, in Params>( private val executionScheduler: Scheduler, private val postExecutionScheduler: Scheduler) { abstract fun buildInteractorCompletable(params: Params): Observable<T> fun execute(params: Params): Observable<T> = buildInteractorObservable(params) .subscribeOn(executionScheduler) .observeOn(postExecutionScheduler) .subscribe() }
33. Interactors class RefreshFeedInteractor @Inject constructor( private val tweetListRepository: TweetListRepository, executionScheduler: Scheduler, postExecutionScheduler: Scheduler) : ObservableInteractor<List<Tweet>, FeedSpec>(executionScheduler, postExecutionScheduler) { override fun buildInteractorCompletable(params: FeedSpec): Observable<List<Tweet>> = tweetListRepository.observeFeed(params) } .filter { it.createdDate.after(someDate) } .compose { customTransformer }
34. interface TweetListRepository { fun refreshFeed(feedSpec: FeedSpec): Completable fun observeFeed(feedSpec: FeedSpec): Observable<List<Tweet>> }
35. class ReactiveTwitterRepository( private val apiMapper: ApiToStoreMapper, 
 private val api: SomeApi, 
 private val store: ReactiveStore) : TweetRepository { override fun refreshFeed(): Completable =
 api.retrieveTweetList()
 .map { apiMapper }
 .doOnSuccess { store.storeTweets(it) }
 .toCompletable() ... }
36. class ReactiveTwitterRepository( private val apiMapper: ApiToStoreMapper, 
 private val domainMapper: StoreToDomainMapper, 
 private val api: SomeApi, 
 private val store: ReactiveStore) : TweetRepository { ... override fun getFeedObservable(feedSpec: FeedSpec):
 Observable<List<Tweet> =
 store.getFeedObservable()
 .map(domainMapper) ... }
37. interface ReactiveStore<Key, Value> { fun storeSingle(item: Value): Completable fun storeAll(items: List<Value>): Completable fun replaceAll(items: List<Value>): Completable fun getSingle(key: Key): Observable<Value> fun getAll(): Observable<List<Value>> } ReactiveStore
38. ReactiveStore ! Coordinates putting data in persistence and/or cache ! Create, store and feed the stream ! Implementation depends on the application ! Single source of truth
39. Domain data flow D A T A action P R E S E N TA T
 I
 O N D O M A I N action reaction reaction
40. Final advices ! Be pragmatic ◦ Some compromises are ok ◦ Perfect isn’t always best ! Beware of technical debt ◦ Every debt will be collected some day ! Start out small ◦ Get a feel for the structure ◦ Decide on whether it’s the best approach for your app ! Don’t forget the tests!
41. Q&A (hopefully) viktor@devies.se Viktor Nyblom @qw4z1