Effective Reactive Architecture

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Benoît Quenaudon @oldergod Effective Reactive Architecture

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Side-Effects Isolation

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class ProfileView { val navigator: Navigator val nameView: TextView val appService: AppService val nameSubject = BehaviorSubject.create() fun onStart() { } }

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class ProfileView { val navigator: Navigator val nameView: TextView val appService: AppService val nameSubject = BehaviorSubject.create() fun onStart() { nameSubject .switchMap { name -> appService.profile() .map { profile -> profile.prefix } .map { profile -> if (name.isEmpty()) "" else "$prefix $name" } } .subscribe(nameView::setText) // hint grows the view in width so hide it if unnecessary nameSubject .map { name -> if (name.isEmpty()) "Set your name" else "" } .subscribe(nameView::setHint) appService.profile().subscribe(this::populateProfile) } }

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fun onStart() { nameSubject .switchMap { name -> appService.profile() .map { profile -> profile.prefix } .map { profile -> if (name.isEmpty()) "" else "$prefix $name" } } .subscribe(nameView::setText) // hint grows the view in width so hide it if unnecessary nameSubject .map { name -> if (name.isEmpty()) "Set your name" else "" } .subscribe(nameView::setHint) appService.profile().subscribe(this::populateProfile) } fun populateProfile(profile: Profile) { nameSubject.onNext(profile.name) // rendering other stuff } fun onSetNameDialogResult(newName: String) = setName(newName) fun setName(newName: String) { nameSubject.onNext(newName) } }

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How about Side Effects?

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class ProfileView { val navigator: Navigator val nameView: TextView val appService: AppService val nameSubject = BehaviorSubject.create() fun onStart() { } }

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class ProfileViewRemix { val navigator: Navigator val nameView: TextView val appService: AppService val nameSubject = BehaviorSubject.create() fun onStart() { } }

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sealed class Event { data class EditName(val newName: String) : Event() }

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sealed class Result { data class ProfileResult(val profile: Profile) : Result() data class NameValid(val name: String) : Result() object NameInvalid : Result() }

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data class ViewModel( val stuff: Any?, val prefixedName: PrefixedName )

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data class ViewModel( val stuff: Any?, val prefixedName: PrefixedName ) { data class PrefixedName( val prefix: String, val name: String ) { fun compute(name:String): String = if (name.isEmpty()) "" else "$prefix $name" } }

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class ProfileViewRemix { val navigator: Navigator val nameView: TextView val appService: AppService val nameSubject = BehaviorSubject.create() fun onStart() { } }

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class ProfileViewRemix { val navigator: Navigator val nameView: TextView val appService: AppService val nameSubject = BehaviorSubject.create() val events = PublishSubject.create() fun onStart() { events.publish { events -> .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } }

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class ProfileViewRemix { val navigator: Navigator val nameView: TextView val appService: AppService val nameSubject = BehaviorSubject.create() val events = PublishSubject.create() fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } } ) } .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } }

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class ProfileViewRemix { val navigator: Navigator val nameView: TextView val appService: AppService val nameSubject = BehaviorSubject.create() val events = PublishSubject.create() fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } }

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class ProfileViewRemix { val navigator: Navigator val nameView: TextView val appService: AppService val nameSubject = BehaviorSubject.create() val events = PublishSubject.create() fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } }

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val nameView: TextView val appService: AppService val nameSubject = BehaviorSubject.create() val events = PublishSubject.create() fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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One Stream Let's organize it

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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fun onStart() { events.publish { events -> Observable.merge( events.filterIsInstance() .switchMap { event -> appService.setName(event.newName).map { response -> when { response.isValid -> NameValid(response.name) response.isInvalid -> NameInvalid.also { navigator.goTo(response) } } } .startWith(NameValid(event.newName)) } ) } .mergeWith(appService.profile().map(::ProfileResult)) .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")), BiFunction { previous: ViewModel, result: Result -> when (result) { is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name)) is NameInvalid -> previous is ProfileResult -> previous.copy( stuff = result.profile, prefixedName = PrefixedName(result.profile.prefix, result.profile.name) ) } }) .subscribe { viewModel -> nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else "" nameView.text = viewModel.prefixedName.compute() // rendering other stuff } } fun onSetNameDialogResult(newName: String) { events.onNext(EditName(newName)) }

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events // Observable .subscribe { viewModel -> }

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events // Observable .subscribe { viewModel -> }

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Passing events to the Presenter

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Option A Passing events to the Presenter

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events .subscribe { viewModel -> } class ProfilePresenter : Consumer { } View Presenter

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events .subscribe { viewModel -> } class ProfilePresenter : Consumer { override fun accept(event: Event) { } } View Presenter

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events.subscribe(presenter) presenter.something().subscribe { viewModel -> } class ProfilePresenter : Consumer { override fun accept(event: Event) { } } View Presenter

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class ProfilePresenter : Consumer { override fun accept(event: Event) { event.flatMap {} } } View Presenter events.subscribe(presenter) presenter.something().subscribe { viewModel -> }

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Option B Passing events to the Presenter

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events. .subscribe { viewModel -> } class ProfilePresenter(val events:Observable) { } View Presenter

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events. .subscribe { viewModel -> } class ProfilePresenter(val events:Observable) { init { events.publish { events -> } } } View Presenter

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presenter(events) .subscribe { viewModel -> } class ProfilePresenter(val events:Observable) { init { events.publish { events -> } } } View Presenter

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Option C Passing events to the Presenter

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presenter.viewModels(events) .subscribe { viewModel -> } class ProfilePresenter { fun viewModels(events: Observable) { events.publish { events -> } } } View Presenter

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Passing view models to the View

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Option A Passing view models to the View

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presenter.viewmodels() .subscribe { viewModel -> } class ProfilePresenter { fun viewmodels(): Observable { } } View Presenter

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Option B Passing view models to the View

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presenter .subscribe { viewModel -> } class ProfilePresenter: Observable() { override fun subscribeActual(observer: Observer) { } } View Presenter

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Option C Passing view models to the View

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presenter .subscribe() class ProfilePresenter: ObservableSource { override fun subscribe(observer: Observer) { } } View Presenter

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presenter .subscribe(object : Observer { override fun onComplete() {} override fun onSubscribe(d: Disposable) {} override fun onNext(t: ViewModel) {} override fun onError(e: Throwable) {} }) class ProfilePresenter: ObservableSource { override fun subscribe(observer: Observer) { } } View Presenter

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Observable.wrap(presenter) .subscribe { viewModel -> } class ProfilePresenter: ObservableSource { override fun subscribe(observer: Observer) { } } View Presenter

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Writing is good. Thinking is better.

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fun presenter()

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fun presenter(events: Observable)

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fun presenter(events: Observable): Observable

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interface ObservableTransformer { /** * Applies a function to the upstream Observable and returns an ObservableSource with * optionally different element type. */ fun apply(upstream: Observable): ObservableSource }

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interface ObservableTransformer { fun apply(upstream: Observable): ObservableSource }

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interface ObservableTransformer { fun apply(events: Observable): ObservableSource }

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interface ObservableTransformer { fun apply(events: Observable): ObservableSource }

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class Presenter: ObservableTransformer { fun apply(events: Observable): ObservableSource }

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class Presenter: ObservableTransformer { fun apply(events: Observable): ObservableSource } events .compose(presenter) .subscribe { viewModel -> } View Presenter

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class Presenter: ObservableTransformer { fun apply(events: Observable): ObservableSource } val testObserver = events // PublishSubject .compose(presenter) .test() // TestObserver Test Presenter

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class Presenter: ObservableTransformer { fun apply(events: Observable): ObservableSource } val testObserver = events // PublishSubject .compose(presenter) .test() // TestObserver events.onNext(EditName("Georges")) testObserver.assertValue(ViewModel()) Test Presenter

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Presenter • Don't break the stream • Don't start work until observed • Doesn't handle disposables* • Has one entry point • Has one exit point

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Thinking is good. Config Changes is better.

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class ProfilePresenter { } View Presenter

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class ProfilePresenter { val events = PublishSubject.create() fun passEvents(events: Observable) { events.subscribe(this.events) } } View Presenter

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class ProfilePresenter { val events = PublishSubject.create() fun passEvents(events: Observable) { events.subscribe(this.events) } fun viewModels() { return events.businessLogic() } } View Presenter

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class ProfilePresenter { val events = PublishSubject.create() fun passEvents(events: Observable) { events.subscribe(this.events) } private val vmObservable : Observable by lazy(NONE) { events.businessLogic() .replay(1) .autoConnect(0) } fun viewModels() = vmObservable } View Presenter

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presenter.viewModels() .subscribe { viewModel -> } View Presenter class ProfilePresenter { val events = PublishSubject.create() fun passEvents(events: Observable) { events.subscribe(this.events) } private val vmObservable : Observable by lazy(NONE) { events.businessLogic() .replay(1) .autoConnect(0) } fun viewModels() = vmObservable }

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presenter.viewModels() .subscribe { viewModel -> } presenter.passEvents(events) View Presenter class ProfilePresenter { val events = PublishSubject.create() fun passEvents(events: Observable) { events.subscribe(this.events) } private val vmObservable : Observable by lazy(NONE) { events.businessLogic() .replay(1) .autoConnect(0) } fun viewModels() = vmObservable }

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Unidirectional Data Flow

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VIEW PRESENTER

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VIEW PRESENTER (BUSINESS LOGIC) READING WRITING

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