badoo.problems.take(5).map { solve(it) }

At Badoo, we have a long history when it comes to Android development. Since the beginning, the product has experienced huge growth, and our codebase and our team have grown with it. We now have over 400 million registrations, as well as several new apps to support. In this talk we’ll go on an architectural journey and discuss some of the major problems we needed to find solutions for in the last few years, before ending on what is ahead of us.

Transcript

1. badoo .problems
 .take(5)
 .map { solve(it) }
2. Zsolt Kocsi Android engineer @ Badoo @ZsoltKocsi
3. Badoo products ? ? ?
4. Problem #1 State
5. 1. MVP Pros Better than nothing Cons Doesn’t scale well
6. 1. MVP
 2. Clean architecture Pros Clear separation of layers Cons ?
7. 1. MVP
 2. Clean architecture Our real problems State-related
9. View Intent Model
10. View Intent Model Model changes Immutable state Reducer Pros Single point of mutation Easier to understand
11. 1. MVP
 2. Clean architecture 3. ??? What we need Immutable state How to do it best ???
12. 1. MVP
 2. Clean architecture 3. Proto-MVI Inspired by Redux Frankenstein’s monster of MVP Clean architecture Immutable state stores RxJava
13. 1. MVP
 2. Clean architecture 3. Proto-MVI Pros Easier to reason about what can happen to the state State problems gone! Cons We needed structure
14. 1. MVP
 2. Clean architecture 3. Proto-MVI
 4. Experiments ???
15. 1. MVP
 2. Clean architecture 3. Proto-MVI 4. Experiments
 5. MVICore https://github.com/badoo/MVICore
16. Feature State machines Reducer only
17. Reducer Feature State machines Reducer only Wish State
18. R Fe class SimpleFeature : ReducerFeature<Wish, State, Nothing>( initialState = State(), reducer = ReducerImpl() ) { data class State( val counter: Int = 0 )£ sealed class Wish { object IncreaseCounter : Wish() data class MultiplyBy(val value: Int) : Wish() }• class ReducerImpl : Reducer<State, Wish> { override fun invoke(state: State, wish: Wish): State = when (wish) { IncreaseCounter -> state.copy( counter = state.counter + 1 )§ is MultiplyBy -> state.copy( counter = state.counter * wish.value )¡ }™ }¢ }
20. Problem #2 Side-effects
21. Reducer Feature State machines Reducer only Side-effects externally Wish State
22. data class State( val isLoading: Boolean = false, valªhasError:ªBoolean = false, val payload: Any? = null )• sealed£class£Wish£{ ¢¢¢¢object StartedLoading : Wish() ∞∞∞∞data class Success(val¶payload:¶Any)¶:¶Wish() §§§§data class Failed(valªthrowable:ªThrowable)ª: Wish() }º class ReducerImpl : Reducer<State, Wish> { override fun invoke(state: State, wish: Wish): State = when (wish) { StartedLoading -> state.copy( isLoading = true )º is Success -> state.copy( isLoading = false, hasError = false, payload = wish.payload )¡ is Failed -> state.copy( isLoading = false, hasError = true )™ R Fe
23. State machines Reducer only Side-effects as loop
 Reducer Feature Command Wish State
24. class Reducer( private val initialState: State = State(), private val ex: Executor ) : StateReducer<State, Message, Effect> { override fun invoke(state: State, msg: Message): Pair<State, Command<Effect>?> = when (msg) { is Reset -> initialState to null is Get -> state to { ex.getSettings(state) }.takeIf { !state.loaded } is Retry -> state.retry() to { ex.getSettings(state)“}.takeIf { state.status == FAILURE } is Updated -> state.change(msg.setting) to { executor.saveSettings()≥}.takeIf { msg.saveImmediately }˜ is Done -> state to { ex.saveSettings(state.getValues(), state.mode) }∫ is Logout -> state to { ex.logout() }å is DeleteAccount -> state to { ex.deleteAccount() }~ is PublicProfile -> state.profile() to { ex.saveAndGet(state.profile()) ±}.takeIf { msg.mode == state.mode }^ is Get -> state.onGet(msg) to null is Save -> state.onSave(msg) to null is Logout -> state to null }@ }£ R Fe
25. Reducer Feature Actor State machines Reducer only Side-effects with Actor Wish State Effect
26. data class State( val isLoading: Boolean = false, valªhasError:ªBoolean = false, val payload: Any? = null )å≈ sealed•class•Wish•{ ••••object•LoadSomething•:•Wish() }Ω sealed£class£Effect£{ ¢¢¢¢object StartedLoading : Effect() ∞∞∞∞data class Success(val¶payload:¶Any)¶:¶Effect() §§§§data class Failed(valªthrowable:ªThrowable)ª:ªEffect() }º R Fe Ac
27. data class State( val isLoading: Boolean = false, valªhasError:ªBoolean = false, val payload: Any? = null )å sealed£class£Effect£{ ¢¢¢¢object StartedLoading : Effect() ∞∞∞∞data class Success(val¶payload:¶Any)¶:¶Effect() §§§§data class Failed(valªthrowable:ªThrowable)ª:ªEffect() }™ class ReducerImpl : Reducer<State, Effect> { override fun invoke(state: State, effect: Effect): State = when (effect) { StartedLoading -> state.copy( isLoading = true ) is Success -> state.copy( isLoading = false, hasError = false, payload = wish.payload ) is Failed -> state.copy( isLoading = false, hasError = true ) R Fe Ac
28. sealed class Wish { object LoadSomething : Wish() }¡ sealed class Effect { object StartedLoading : Effect() data class Success(val payload: Any) : Effect() data class Failed(val throwable: Throwable) : Effect() }™ class ActorImpl : Actor<State, Wish, Effect> { private val service: () -> Single<Any> = TODO() override fun invoke(state: State, wish: Wish): Observable<out Effect> = when (wish) { is LoadSomething -> service.invoke() .toObservable() .map { Success(it) as Effect } .startWith(Observable.just(StartedLoading)) .onErrorReturn { Failed(it) } }£ }º R Fe Ac
29. class AsyncFeature : ActorReducerFeature<Wish, Effect, State, Nothing>( initialState = State(), actor = ActorImpl(), reducer = ReducerImpl() ) R Fe Ac
30. Problem #3 Events
31. R Fe Ac data class State( val isLoading: Boolean = false, valªhasError:ªBoolean = false, val payload: Any? = null )å class ReducerImpl : Reducer<State, Effect> { override fun invoke(state: State, effect: Effect): State = when (effect) { is Failed -> state.copy( isLoading = false, hasError = true ) valªhasError:ªBoolean )å is Failed -> state.copy( hasError = true )
32. if (state.hasError) { showToast() }º R Fe Ac
33. State machines Reducer only Side-effects with Actor Events
34. State machines Reducer only Side-effects with Actor Events
35. State machines Reducer only Side-effects with Actor Events
36. dev: forgets to reset the flag toast: *shows again* dev:
37. Reducer Feature Actor State machines Reducer only Side-effects with Actor Events Wish State Effect
38. News Publ. Reducer Feature Actor State machines Reducer only Side-effects with Actor Events Wish State Effect News
39. News Publ. Reducer Feature Actor State machines Reducer only Side-effects with Actor Events Wish State Effect News
40. class AsyncFeature : ActorReducerFeature<Wish, Effect, State, News>( initialState = State(), actor = ActorImpl(), reducer = ReducerImpl(), newsPublisher = NewsPublisherImpl() )π{ sealed class News { data class NetworkRequestFailed(val throwable: Throwable) : News() }£ class NewsPublisherImpl : NewsPublisher<Wish, Effect, State, News> { override fun invoke(wish: Wish, effect: Effect, state: State): News? = when (effect) { is Failed -> News.NetworkRequestFailed( effect.throwable ) else -> null }™ }¡ }º F N R A W S E N
41. feature.news .subscribe { when (it) { is News.NetworkRequestFailed -> { showToast() } }} F N R A W S E N
42. Problem #4 Connecting Components of Business Logic
43. Data-flow Coupling Scoping Connecting Components of Business Logic
44. Data-flow
45. Connecting components Data-flow F V Pros Easy
46. F V Y X Pros Easy Cons No single-source of truth Connecting components Data-flow
47. F V Connecting components Data-flow
48. Pros Single source of truth! Better control over flow F V Y X Connecting components Data-flow
49. fun connect() { val source = Observable.just(1, 2, 3) val consumer = Consumer<Int> { Log.d("New number!", it.toString()) }¢ val disposable = source.subscribe(consumer) }ƒ
50. package io.reactivex; /** * Represents a basic, non-backpressured {@link Observab * consumable via an {@link Observer}. * * @param <T> the element type * @since 2.0 */ public interface ObservableSource<T> { /** * Subscribes the given Observer to this ObservableS * @param observer the Observer, not null * @throws NullPointerException if {@code observer} */ void subscribe(@NonNull Observer<? super T> observer); }
51. package io.reactivex.functions; /** * A functional interface (callback) that accepts a singl * @param <T> the value type */ public interface Consumer<T> { /** * Consume the given value. * @param t the value * @throws Exception on error */ void accept(T t) throws Exception; }
52. interface Feature : Consumer<Wish>, ObservableSource<State> { sealed class Wish data class State }£ interface View : Consumer<State>, ObservableSource<Wish> { }¡
53. Data-flow Coupling Scoping Connecting Components of Business Logic
54. Coupling
55. interface Feature : Consumer<Wish>, ObservableSource<State> { sealed class Wish data class State } interface View : Consumer<State>, ObservableSource<Wish> { }
56. interface Feature : Consumer<Wish>, ObservableSource<State> { sealed class Wish data class State } interface View : Consumer<ViewModel>, ObservableSource<View.Event> { data class ViewModel sealed class Event }
57. F V Pros No coupling :) Cons ? Connecting components Data-flow Coupling
58. /** * Gluing layer between UI and Feature */ interface Boundary<in UiEvent : Any, ViewModel : Any> : Disposable { fun onUiEvent(uiEvent: UiEvent) val viewModels: Observable<ViewModel> } Connecting components Data-flow Coupling
59. Pros No coupling :) Cons Not flexible :( F V F ??? Connecting components Data-flow Coupling
60. Pros No coupling :) Cons Not flexible :( F F ??? Connecting components Data-flow Coupling
61. Pros No coupling :) Cons Not flexible :( F V X Y ??? Connecting components Data-flow Coupling
62. Data-flow Coupling Scoping Connecting Components of Business Logic
63. Scoping
64. Connecting components Data-flow Coupling Scoping
65. F V V X Y F V Connecting components Data-flow Coupling Scoping
66. F V V X Y F V Connecting components Data-flow Coupling Scoping
67. F V V X Y F V Connecting components Data-flow Coupling Scoping
68. val output: ObservableSource<String> = Observable.just( "item1", "item2", "item3" )£ val input: Consumer<String> = Consumer { System.out.println(it) }£ val disposable = Observable .wrap(output) .subscribe(input)
69. val output: ObservableSource<String> = Observable.just( "item1", "item2", "item3" )£ val input: Consumer<String> = Consumer { System.out.println(it) }£ val binder = Binder() binder.bind(output to input)
70. val output: ObservableSource<String> = Observable.just( "item1", "item2", "item3" )£ val input: Consumer<Int> = Consumer { System.out.println(it) }£ val transformer : (String) -> Int = { it.length }£ val binder = Binder() binder.bind(output to input using transformer)
71. binder.bind(view to feature using EventToWish)£ binder.bind(feature to view using StateToViewModel) binder.bind(feature to greenX using StateToGX) binder.bind(feature to greenY using StateToGY)
72. binder.bind(view to analyticsTracker) binder.bind(view to feature using EventToWish) binder.bind(feature to view using StateToViewModel) binder.bind(feature to greenX using StateToGX) binder.bind(feature to greenY using StateToGY) binder.bind(view to analyticsTracker)
73. val lifecycle: Lifecycle = TODO() val binder = Binder(lifecycle)£ binder.bind(view to analyticsTracker) binder.bind(view to feature using EventToWish) binder.bind(feature to view using StateToViewModel) binder.bind(feature to greenX using StateToGX) binder.bind(feature to greenY using StateToGY)
74. C S Begin End Begin End Connecting components Data-flow Coupling Scoping
75. C S Lifecycle sources Android / Create-Destroy Android / Start-Stop Android / Resume-Pause From Observable Manual Connecting components Data-flow Coupling Scoping
76. F V V X Y F V Connecting components Data-flow Coupling Scoping
77. X F F Connecting components Data-flow Coupling Scoping
78. F V V X Y F V Connecting components Data-flow Coupling Scoping
79. F X F V A Connecting components Data-flow Coupling Scoping
80. binder.bind(view to analyticsTracker) binder.bind(view to feature using EventToWish) binder.bind(feature to view using StateToViewModel) binder.bind(feature to greenX using StateToGX) binder.bind(feature to greenY using StateToGY)
81. Problem #5 Cross-cutting concerns
82. Cross-cutting concerns
83. Cross-cutting concerns
84. Cross-cutting concerns
85. package io.reactivex.functions; /** * A functional interface (callback) that accepts a singl * @param <T> the value type */ public interface Consumer<T> { /** * Consume the given value. * @param t the value * @throws Exception on error */ void accept(T t) throws Exception; }
86. abstract class Middleware<T>¡{ }º
87. abstract class Middleware<T> : Consumer<T>¡{ override fun accept(t: T) { }& }º
88. abstract class Middleware<T>( private val wrapped: Consumer<T> ) : Consumer<T>¡{ override fun accept(t: T) { // do whatever here wrapped.accept(t) // do whatever here }& }º
89. abstract class Middleware<T>( private val wrapped: Consumer<T> ) : Consumer<T>¡{ override fun accept(t: T) { // Log it! wrapped.accept(t) }& }º
90. abstract class Middleware<T>( private val wrapped: Consumer<T> ) : Consumer<T>¡{ override fun accept(t: T) { // Save it somewhere for later! wrapped.accept(t) }& }º
91. Cross-cutting concerns
92. Cross-cutting concerns
93. What’s behind us
94. 1. Simple state reducing 2. Side-effects 3. Events Feature
95. 1. Simple state reducing 2. Side-effects 3. Events 4. Coupling 5. Scoping
96. 1. Simple state reducing 2. Side-effects 3. Events 4. Coupling 5. Scoping 6. Middlewares
97. 1. Simple state reducing 2. Side-effects 3. Events 5. Coupling 6. Scoping 7. Middlewares https://github.com/badoo/MVICore
98. Problem #N What the future holds
99. Additional resources GitHub project https://github.com/badoo/MVICore Article about Features https://badootech.badoo.com/a-modern-kotlin-based-mvi- architecture-9924e08efab1 Article about Binder https://badootech.badoo.com/building-a-system-of-reactive- components-with-kotlin-ff56981e92cf Time Travel Debugger Demo https://badootech.badoo.com/time-travel-debug-everything- droidconuk-2018-lightning-talk-445217258401
100. github.com/zsoltk @ZsoltKocsi medium.com/@zsolt.kocsi linkedin.com/in/zsolt-kocsi #MVICore Thank you!