Applying Rx Best Practices to Your Architecture

Video: https://youtu.be/ohBumH5-3Qs

Your relationship with RxJava doesn't have to be complicated. We find many ways to use it wrong; it is also powerful when used properly. In fact, RxJava can guide you in shaping a sound architecture for your app. We only have to follow a few but decisive principles.

In this talk, we'll:

- See at how side-effect isolation can help avoiding bugs.
- Learn how to share one unique stream between your view and your presenter.
- Discover the ways a unidirectional data flow makes adding new functionality easy and safe.
- Look at how data immutability brings safety to data manipulation.

After this talk, you’ll be able to write a robust and reactive architecture for your app, taking full advantage of RxJava.

Transcript

1. Benoît Quenaudon @oldergod
   Applying Rx Best Practices
   to your Architecture
   

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2. Side-Effects Isolation
   

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

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4. class ProfileView {a
   val navigator: Navigator
   val nameView: TextView
   val appService: AppService
   val nameSubject = BehaviorSubject.create()
   fun onStart() {k
   nameSubject@
   .switchMap { name ->
   appService.profile()
   .map { profile -> profile.prefix }
   .map { profile -> if (name.isEmpty()) "" else "$prefix $name" }
   }j
   .subscribe(nameView::setText)
   }i
   }z
   

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5. class ProfileView {a
   val navigator: Navigator
   val nameView: TextView
   val appService: AppService
   val nameSubject = BehaviorSubject.create()
   fun onStart() {k
   nameSubject@
   .switchMap { name ->
   appService.profile()
   .map { profile -> profile.prefix }
   .map { profile -> if (name.isEmpty()) "" else "$prefix $name" }
   }j
   .subscribe(nameView::setText)
   nameSubject
   .map { name -> if (name.isEmpty()) "Set your name" else "" }
   .subscribe(nameView::setHint)
   }i
   }z
   

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6. class ProfileView {a
   val navigator: Navigator
   val nameView: TextView
   val appService: AppService
   val nameSubject = BehaviorSubject.create()
   fun onStart() {k
   nameSubject@
   .switchMap { name ->
   appService.profile()
   .map { profile -> profile.prefix }
   .map { profile -> if (name.isEmpty()) "" else "$prefix $name" }
   }j
   .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)
   }i
   }z
   

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7. class ProfileView {a
   val navigator: Navigator
   val nameView: TextView
   val appService: AppService
   val nameSubject = BehaviorSubject.create()
   fun onStart() {k
   nameSubject@
   .switchMap { name ->
   appService.profile()
   .map { profile -> profile.prefix }
   .map { profile -> if (name.isEmpty()) "" else "$prefix $name" }
   }j
   .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)
   }i
   }z
   

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8. class ProfileView {a
   val navigator: Navigator
   val nameView: TextView
   val appService: AppService
   val nameSubject = BehaviorSubject.create()
   fun onStart() {k
   nameSubject
   .switchMap { name ->
   appService.profile()
   .map { profile -> profile.prefix }
   .map { profile -> if (name.isEmpty()) "" else "$prefix $name" }
   }j
   .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)
   }i
   fun populateProfile(profile: Profile) {h
   nameSubject.onNext(profile.name)
   // rendering other stuff
   }g
   }z
   

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9. class ProfileView {a
   val navigator: Navigator
   val nameView: TextView
   val appService: AppService
   val nameSubject = BehaviorSubject.create()
   fun onStart() {k
   nameSubject
   .switchMap { name ->
   appService.profile()
   .map { profile -> profile.prefix }
   .map { profile -> if (name.isEmpty()) "" else "$prefix $name" }
   }j
   .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)
   }i
   fun populateProfile(profile: Profile) {h
   nameSubject.onNext(profile.name)
   // rendering other stuff
   }g
   fun onSetNameDialogResult(newName: String) = setName(newName)
   }z
   

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10. val appService: AppService
    val nameSubject = BehaviorSubject.create()
    fun onStart() {k
    nameSubject
    .switchMap { name ->
    appService.profile()
    .map { profile -> profile.prefix }
    .map { profile -> if (name.isEmpty()) "" else "$prefix $name" }
    }j
    .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)
    }i
    fun populateProfile(profile: Profile) {h
    nameSubject.onNext(profile.name)
    // rendering other stuff
    }g
    fun onSetNameDialogResult(newName: String) = setName(newName)
    fun setName(newName: String) {f
    nameSubject.onNext(newName)
    }b
    }z
    

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11. fun onStart() {k
    nameSubject
    .switchMap { name ->
    appService.profile()
    .map { profile -> profile.prefix }
    .map { profile -> if (name.isEmpty()) "" else "$prefix $name" }
    }j
    .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)
    }i
    fun populateProfile(profile: Profile) {h
    nameSubject.onNext(profile.name)
    // rendering other stuff
    }g
    fun onSetNameDialogResult(newName: String) = setName(newName)
    fun setName(newName: String) {f
    nameSubject.onNext(newName)
    appService.setName(newName)
    .subscribe { response ->
    when {e
    response.isValid -> nameSubject.onNext(response.name)
    response.isInvalid -> navigator.goTo(response.error)
    }d
    }c
    }b
    

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12. fun onStart() {k
    nameSubject
    .switchMap { name ->
    appService.profile()
    .map { profile -> profile.prefix }
    .map { profile -> if (name.isEmpty()) "" else "$prefix $name" }
    }j
    .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)
    }i
    fun populateProfile(profile: Profile) {h
    nameSubject.onNext(profile.name)
    // rendering other stuff
    }g
    fun onSetNameDialogResult(newName: String) = setName(newName)
    fun setName(newName: String) {f
    nameSubject.onNext(newName)
    appService.setName(newName)
    .subscribe { response ->
    when {e
    response.isValid -> nameSubject.onNext(response.name)
    response.isInvalid -> navigator.goTo(response.error)
    }d
    }c
    }b
    

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13. fun onStart() {k
    nameSubject
    .switchMap { name ->
    appService.profile()
    .map { profile -> profile.prefix }
    .map { profile -> if (name.isEmpty()) "" else "$prefix $name" }
    }j
    .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)
    }i
    fun populateProfile(profile: Profile) {h
    nameSubject.onNext(profile.name)
    // rendering other stuff
    }g
    fun onSetNameDialogResult(newName: String) = setName(newName)
    fun setName(newName: String) {f
    nameSubject.onNext(newName)
    appService.setName(newName)
    .subscribe { response ->
    when {e
    response.isValid -> nameSubject.onNext(response.name)
    response.isInvalid -> navigator.goTo(response.error)
    }d
    }c
    }b
    

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14. fun onStart() {k
    nameSubject
    .switchMap { name ->
    appService.profile()
    .map { profile -> profile.prefix }
    .map { profile -> if (name.isEmpty()) "" else "$prefix $name" }
    }j
    .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)
    }i
    fun populateProfile(profile: Profile) {h
    nameSubject.onNext(profile.name)
    // rendering other stuff
    }g
    fun onSetNameDialogResult(newName: String) = setName(newName)
    fun setName(newName: String) {f
    nameSubject.onNext(newName)
    appService.setName(newName)
    .subscribe { response ->
    when {e
    response.isValid -> nameSubject.onNext(response.name)
    response.isInvalid -> navigator.goTo(response.error)
    }d
    }c
    }b
    

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15. How about Side Effects?
    

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16. fun onStart() {k
    nameSubject
    .switchMap { name ->
    appService.profile()
    .map { profile -> profile.prefix }
    .map { profile -> if (name.isEmpty()) "" else "$prefix $name" }
    }j
    .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)
    }i
    fun populateProfile(profile: Profile) {h
    nameSubject.onNext(profile.name)
    // rendering other stuff
    }g
    fun onSetNameDialogResult(newName: String) = setName(newName)
    fun setName(newName: String) {f
    nameSubject.onNext(newName)
    appService.setName(newName)
    .subscribe { response ->
    when {e
    response.isValid -> nameSubject.onNext(response.name)
    response.isInvalid -> navigator.goTo(response.error)
    }d
    }c
    }b
    

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17. fun onStart() {k
    nameSubject
    .switchMap { name ->
    appService.profile()
    .map { profile -> profile.prefix }
    .map { profile -> if (name.isEmpty()) "" else "$prefix $name" }
    }j
    .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)
    }i
    fun populateProfile(profile: Profile) {h
    nameSubject.onNext(profile.name)
    // rendering other stuff
    }g
    fun onSetNameDialogResult(newName: String) = setName(newName)
    fun setName(newName: String) {f
    nameSubject.onNext(newName)
    appService.setName(newName)
    .subscribe { response ->
    when {e
    response.isValid -> nameSubject.onNext(response.name)
    response.isInvalid -> navigator.goTo(response.error)
    }d
    }c
    }b
    

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

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

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

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

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

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

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24. class ProfileViewRemix {a
    val navigator: Navigator
    val nameView: TextView
    val appService: AppService
    val nameSubject = BehaviorSubject.create()
    val events = PublishSubject.create()
    fun onStart() {t
    events.flatMap { event ->
    }i
    }t
    

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25. class ProfileViewRemix {a
    val navigator: Navigator
    val nameView: TextView
    val appService: AppService
    val nameSubject = BehaviorSubject.create()
    val events = PublishSubject.create()
    fun onStart() {t
    events.flatMap { event ->
    .subscribe { viewModel ->
    }o
    }i
    }t
    

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

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27. class ProfileViewRemix {a
    val navigator: Navigator
    val nameView: TextView
    val appService: AppService
    val nameSubject = BehaviorSubject.create()
    val events = PublishSubject.create()
    fun onStart() {t
    events.flatMap { event ->
    when (event) {y
    is EditName ->
    }g
    }h
    .subscribe { viewModel ->
    nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else ""
    nameView.text = viewModel.prefixedName.compute()
    // rendering other stuff
    }o
    }i
    }t
    

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28. class ProfileViewRemix {a
    val navigator: Navigator
    val nameView: TextView
    val appService: AppService
    val nameSubject = BehaviorSubject.create()
    val events = PublishSubject.create()
    fun onStart() {t
    events.flatMap { event ->
    when (event) {y
    is EditName -> appService.setName(event.newName)
    .map { response ->
    when {u
    response.isValid -> NameValid(response.name)
    response.isInvalid -> NameInvalid.also { navigator.goTo(response) }
    }d
    }f
    }g
    }h
    .subscribe { viewModel ->
    nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else ""
    nameView.text = viewModel.prefixedName.compute()
    // rendering other stuff
    }o
    }i
    }t
    

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29. class ProfileViewRemix {a
    val navigator: Navigator
    val nameView: TextView
    val appService: AppService
    val nameSubject = BehaviorSubject.create()
    val events = PublishSubject.create()
    fun onStart() {t
    events.flatMap { event ->
    when (event) {y
    is EditName -> appService.setName(event.newName)
    .map { response ->
    when {u
    response.isValid -> NameValid(response.name)
    response.isInvalid -> NameInvalid.also { navigator.goTo(response) }
    }d
    }f
    .startWith(NameValid(event.newName))
    }g
    }h
    .subscribe { viewModel ->
    nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else ""
    nameView.text = viewModel.prefixedName.compute()
    // rendering other stuff
    }o
    }i
    }t
    

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30. class ProfileViewRemix {a
    val navigator: Navigator
    val nameView: TextView
    val appService: AppService
    val nameSubject = BehaviorSubject.create()
    val events = PublishSubject.create()
    fun onStart() {t
    events.flatMap { event ->
    when (event) {y
    is EditName -> appService.setName(event.newName)
    .map { response ->
    when {u
    response.isValid -> NameValid(response.name)
    response.isInvalid -> NameInvalid.also { navigator.goTo(response) }
    }d
    }f
    .startWith(NameValid(event.newName))
    }g
    }h
    .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
    }o
    }i
    }t
    

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31. val nameView: TextView
    val appService: AppService
    val nameSubject = BehaviorSubject.create()
    val events = PublishSubject.create()
    fun onStart() {t
    events.flatMap { event ->
    when (event) {y
    is EditName -> appService.setName(event.newName)
    .map { response ->
    when {u
    response.isValid -> NameValid(response.name)
    response.isInvalid -> NameInvalid.also { navigator.goTo(response) }
    }d
    }f
    .startWith(NameValid(event.newName))
    }g
    }h
    .mergeWith(appService.profile().map(::ProfileResult))
    .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
    BiFunction { previous: ViewModel, result: Result ->
    })p
    .subscribe { viewModel ->
    nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else ""
    nameView.text = viewModel.prefixedName.compute()
    // rendering other stuff
    }o
    }i
    }t
    

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32. val nameView: TextView
    val appService: AppService
    val nameSubject = BehaviorSubject.create()
    val events = PublishSubject.create()
    fun onStart() {t
    events.flatMap { event ->
    when (event) {y
    is EditName -> appService.setName(event.newName)
    .map { response ->
    when {u
    response.isValid -> NameValid(response.name)
    response.isInvalid -> NameInvalid.also { navigator.goTo(response) }
    }d
    }f
    .startWith(NameValid(event.newName))
    }g
    }h
    .mergeWith(appService.profile().map(::ProfileResult))
    .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
    BiFunction { previous: ViewModel, result: Result ->
    })p
    .subscribe { viewModel ->
    nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else ""
    nameView.text = viewModel.prefixedName.compute()
    // rendering other stuff
    }o
    }i
    }t
    

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33. val events = PublishSubject.create()
    fun onStart() {t
    events.flatMap { event ->
    when (event) {y
    is EditName -> appService.setName(event.newName)
    .map { response ->
    when {u
    response.isValid -> NameValid(response.name)
    response.isInvalid -> NameInvalid.also { navigator.goTo(response) }
    }d
    }f
    .startWith(NameValid(event.newName))
    }g
    }h
    .mergeWith(appService.profile().map(::ProfileResult))
    .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
    BiFunction { previous: ViewModel, result: Result ->
    when (result) {j
    is NameValid -> previous.copy(prefixedName = previous.prefixedName.copy(name = result.name))
    is NameInvalid -> previous
    }l
    })p
    .subscribe { viewModel ->
    nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else ""
    nameView.text = viewModel.prefixedName.compute()
    // rendering other stuff
    }o
    }i
    }t
    

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34. fun onStart() {t
    events.flatMap { event ->
    when (event) {y
    is EditName -> appService.setName(event.newName)
    .map { response ->
    when {u
    response.isValid -> NameValid(response.name)
    response.isInvalid -> NameInvalid.also { navigator.goTo(response) }
    }d
    }f
    .startWith(NameValid(event.newName))
    }g
    }h
    .mergeWith(appService.profile().map(::ProfileResult))
    .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
    BiFunction { previous: ViewModel, result: Result ->
    when (result) {j
    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)
    )k
    }l
    })p
    .subscribe { viewModel ->
    nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else ""
    nameView.text = viewModel.prefixedName.compute()
    // rendering other stuff
    }o
    

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35. fun onStart() {t
    events.flatMap { event ->
    when (event) {y
    is EditName -> appService.setName(event.newName)
    .map { response ->
    when {u
    response.isValid -> NameValid(response.name)
    response.isInvalid -> NameInvalid.also { navigator.goTo(response) }
    }d
    }f
    .startWith(NameValid(event.newName))
    }g
    }h
    .mergeWith(appService.profile().map(::ProfileResult))
    .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
    BiFunction { previous: ViewModel, result: Result ->
    when (result) {j
    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)
    )k
    }l
    })p
    .subscribe { viewModel ->
    nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else ""
    nameView.text = viewModel.prefixedName.compute()
    // rendering other stuff
    }o
    }i
    fun onSetNameDialogResult(newName: String) {u
    events.onNext(EditName(newName))
    }y
    }t
    

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36. fun onStart() {t
    events.flatMap { event ->
    when (event) {y
    is EditName -> appService.setName(event.newName)
    .map { response ->
    when {u
    response.isValid -> NameValid(response.name)
    response.isInvalid -> NameInvalid.also { navigator.goTo(response) }
    }d
    }f
    .startWith(NameValid(event.newName))
    }g
    }h
    .mergeWith(appService.profile().map(::ProfileResult))
    .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
    BiFunction { previous: ViewModel, result: Result ->
    when (result) {j
    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)
    )k
    }l
    })p
    .subscribe { viewModel ->
    nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else ""
    nameView.text = viewModel.prefixedName.compute()
    // rendering other stuff
    }o
    }i
    fun onSetNameDialogResult(newName: String) {u
    events.onNext(EditName(newName))
    }y
    }t
    

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37. fun onStart() {t
    events.flatMap { event ->
    when (event) {y
    is EditName -> appService.setName(event.newName)
    .map { response ->
    when {u
    response.isValid -> NameValid(response.name)
    response.isInvalid -> NameInvalid.also { navigator.goTo(response) }
    }d
    }f
    .startWith(NameValid(event.newName))
    }g
    }h
    .mergeWith(appService.profile().map(::ProfileResult))
    .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
    BiFunction { previous: ViewModel, result: Result ->
    when (result) {j
    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)
    )k
    }l
    })p
    .subscribe { viewModel ->
    nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else ""
    nameView.text = viewModel.prefixedName.compute()
    // rendering other stuff
    }o
    }i
    fun onSetNameDialogResult(newName: String) {u
    events.onNext(EditName(newName))
    }y
    

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38. fun onStart() {t
    events.flatMap { event ->
    when (event) {y
    is EditName -> appService.setName(event.newName)
    .map { response ->
    when {u
    response.isValid -> NameValid(response.name)
    response.isInvalid -> NameInvalid.also { navigator.goTo(response) }
    }d
    }f
    .startWith(NameValid(event.newName))
    }g
    }h
    .mergeWith(appService.profile().map(::ProfileResult))
    .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
    BiFunction { previous: ViewModel, result: Result ->
    when (result) {j
    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)
    )k
    }l
    })p
    .subscribe { viewModel ->
    nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else ""
    nameView.text = viewModel.prefixedName.compute()
    // rendering other stuff
    }o
    }i
    fun onSetNameDialogResult(newName: String) {u
    events.onNext(EditName(newName))
    }y
    

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39. fun onStart() {t
    events.flatMap { event ->
    when (event) {y
    is EditName -> appService.setName(event.newName)
    .map { response ->
    when {u
    response.isValid -> NameValid(response.name)
    response.isInvalid -> NameInvalid.also { navigator.goTo(response) }
    }d
    }f
    .startWith(NameValid(event.newName))
    }g
    }h
    .mergeWith(appService.profile().map(::ProfileResult))
    .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
    BiFunction { previous: ViewModel, result: Result ->
    when (result) {j
    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)
    )k
    }l
    })p
    .subscribe { viewModel ->
    nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else ""
    nameView.text = viewModel.prefixedName.compute()
    // rendering other stuff
    }o
    }i
    fun onSetNameDialogResult(newName: String) {u
    events.onNext(EditName(newName))
    }y
    

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40. fun onStart() {t
    events.flatMap { event ->
    when (event) {y
    is EditName -> appService.setName(event.newName)
    .map { response ->
    when {u
    response.isValid -> NameValid(response.name)
    response.isInvalid -> NameInvalid.also { navigator.goTo(response) }
    }d
    }f
    .startWith(NameValid(event.newName))
    }g
    }h
    .mergeWith(appService.profile().map(::ProfileResult))
    .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
    BiFunction { previous: ViewModel, result: Result ->
    when (result) {j
    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)
    )k
    }l
    })p
    .subscribe { viewModel ->
    nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else ""
    nameView.text = viewModel.prefixedName.compute()
    // rendering other stuff
    }o
    }i
    fun onSetNameDialogResult(newName: String) {u
    events.onNext(EditName(newName))
    }y
    

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41. One Stream
    Many Options
    

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42. fun onStart() {t
    events.flatMap { event ->
    when (event) {y
    is EditName -> appService.setName(event.newName)
    .map { response ->
    when {u
    response.isValid -> NameValid(response.name)
    response.isInvalid -> NameInvalid.also { navigator.goTo(response) }
    }d
    }f
    .startWith(NameValid(event.newName))
    }g
    }h
    .mergeWith(appService.profile().map(::ProfileResult))
    .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
    BiFunction { previous: ViewModel, result: Result ->
    when (result) {j
    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)
    )k
    }l
    })p
    .subscribe { viewModel ->
    nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else ""
    nameView.text = viewModel.prefixedName.compute()
    // rendering other stuff
    }o
    }i
    fun onSetNameDialogResult(newName: String) {u
    events.onNext(EditName(newName))
    }y
    

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43. fun onStart() {t
    events.flatMap { event ->
    when (event) {y
    is EditName -> appService.setName(event.newName)
    .map { response ->
    when {u
    response.isValid -> NameValid(response.name)
    response.isInvalid -> NameInvalid.also { navigator.goTo(response) }
    }d
    }f
    .startWith(NameValid(event.newName))
    }g
    }h
    .mergeWith(appService.profile().map(::ProfileResult))
    .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
    BiFunction { previous: ViewModel, result: Result ->
    when (result) {j
    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)
    )k
    }l
    })p
    .subscribe { viewModel ->
    nameView.hint = if (viewModel.prefixedName.name.isEmpty()) "Set your name" else ""
    nameView.text = viewModel.prefixedName.compute()
    // rendering other stuff
    }o
    }i
    fun onSetNameDialogResult(newName: String) {u
    events.onNext(EditName(newName))
    }y
    

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44. events // Observable
    .subscribe { viewModel ->
    }o
    

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45. events // Observable
    
    .subscribe { viewModel ->
    }o
    

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46. Passing events to the Presenter
    

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47. Option A
    Passing events to the Presenter
    

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

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

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

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

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52. Observable.just(1, 2, 3)
    .subscribe { int ->
    Observable.just(int * 3)
    .subscribe { println(it) }
    }
    

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53. Option B
    Passing events to the Presenter
    

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

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55. events.
    .subscribe { viewModel ->
    }o
    class ProfilePresenter(val events:Observable) {
    init {
    events.flatMap { event -> }
    }a
    }z
    View
    Presenter
    

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56. presenter(events)
    .subscribe { viewModel ->
    }o
    class ProfilePresenter(val events:Observable) {
    init {
    events.flatMap { event -> }
    }a
    }z
    View
    Presenter
    

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57. Option C
    Passing events to the Presenter
    

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58. presenter.somefunction(events)
    .subscribe { viewModel ->
    }o
    class ProfilePresenter {
    fun somefunction(events: Observable) {
    events.flatMap { event -> }
    }
    }
    View
    Presenter
    

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59. Passing view models
    to the View
    

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60. Option A
    Passing view models to the View
    

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

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62. Option B
    Passing view models to the View
    

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

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64. Option C
    Passing view models to the View
    

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

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66. 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) {
    }a
    }z
    View
    Presenter
    

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

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68. Writing is good.
    Thinking is better.
    

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69. fun presenter():
    

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70. fun presenter(events: Observable):
    

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71. fun presenter(events: Observable): Observable
    

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

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73. interface ObservableTransformer {a
    fun apply(upstream: Observable): ObservableSource
    }b
    

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74. interface ObservableTransformer {a
    fun apply(events: Observable): ObservableSource
    }b
    

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75. interface ObservableTransformer {a
    fun apply(events: Observable): ObservableSource
    }b
    

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76. class Presenter: ObservableTransformer {a
    fun apply(events: Observable): ObservableSource
    }b
    

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

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

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

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80. Thinking is good.
    Config Changes is better.
    

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81. presenter.viewModels()
    .subscribe { viewModel ->
    }o
    class ProfilePresenter {j
    }u
    View
    Presenter
    

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82. presenter.viewModels()
    .subscribe { viewModel ->
    }o
    class ProfilePresenter {j
    val events = PublishSubject.create()
    fun passEvents(events: Observable) {k
    events.subscribe(this.events)
    }l
    }u
    View
    Presenter
    

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83. presenter.viewModels()
    .subscribe { viewModel ->
    }o
    class ProfilePresenter {j
    val events = PublishSubject.create()
    fun passEvents(events: Observable) {k
    events.subscribe(this.events)
    }l
    fun viewModels() {o
    return events

    .businessLogic()
    }i
    }u
    View
    Presenter
    

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84. presenter.viewModels()
    .subscribe { viewModel ->
    }o
    class ProfilePresenter {j
    val events = PublishSubject.create()
    fun passEvents(events: Observable) {k
    events.subscribe(this.events)
    }l
    fun viewModels() {o
    return events

    .businessLogic()

    .replay(1)

    .autoConnect(0)
    }i
    }u
    View
    Presenter
    

    View Slide

85. presenter.viewModels()
    .subscribe { viewModel ->
    }o
    class ProfilePresenter {j
    val events = PublishSubject.create()
    fun passEvents(events: Observable) {k
    events.subscribe(this.events)
    }l
    fun viewModels() {o
    return events

    .businessLogic()

    .replay(1)

    .autoConnect(0)
    }i
    }u
    View
    Presenter
    

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86. presenter.viewModels()
    .subscribe { viewModel ->
    }o

    presenter.passEvents(events)
    class ProfilePresenter {j
    val events = PublishSubject.create()
    fun passEvents(events: Observable) {k
    events.subscribe(this.events)
    }l
    fun viewModels() {o
    return events

    .businessLogic()

    .replay(1)

    .autoConnect(0)
    }i
    }u
    View
    Presenter
    

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87. Unidirectional
    Data
    Flow
    

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88. VIEW
    PRESENTER
    

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89. VIEW
    PRESENTER (BUSINESS LOGIC)
    READING
    WRITING
    

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90. VIEW
    PRESENTER (BUSINESS LOGIC)
    VIEW (READING) VIEW (WRITING)
    

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91. VIEW (READING)
    VIEW (WRITING)
    PRESENTER (BUSINESS LOGIC)
    

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92. VIEW (READING)
    VIEW (WRITING)
    PRESENTER (BUSINESS LOGIC)
    

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93. New Feature?
    No Problem.
    

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94. sealed class Event {
    data class EditName(val newName: String) : Event()
    }a
    data class ViewModel(
    val stuff: Any?,
    val prefixedName: PrefixedName
    )b
    class ProfileViewRemix {
    fun onStart() {t
    events
    .compose(presenter)
    .subscribe { viewModel ->
    // rendering view model
    }o
    }i
    }t
    

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95. sealed class Event {
    data class EditName(val newName: String) : Event()
    }a
    data class ViewModel(
    val stuff: Any?,
    val prefixedName: PrefixedName
    )b
    class ProfileViewRemix {
    fun onStart() {t
    events
    .compose(presenter)
    .subscribe { viewModel ->
    // rendering view model
    }o
    }i
    }t
    

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96. sealed class Event {
    data class EditName(val newName: String) : Event()
    data class ChangeAvatar(val picture: File) : Event()
    }a
    data class ViewModel(
    val stuff: Any?,
    val prefixedName: PrefixedName
    )b
    class ProfileViewRemix {
    fun onStart() {t
    events
    .compose(presenter)
    .subscribe { viewModel ->
    // rendering view model
    }o
    }i
    }t
    

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97. sealed class Event {
    data class EditName(val newName: String) : Event()
    data class ChangeAvatar(val picture: File) : Event()
    }a
    data class ViewModel(
    val stuff: Any?,
    val prefixedName: PrefixedName,
    val avatarUri: Uri
    )b
    class ProfileViewRemix {
    fun onStart() {t
    events
    .compose(presenter)
    .subscribe { viewModel ->
    // rendering view model
    }o
    }i
    }t
    

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98. sealed class Event {
    data class EditName(val newName: String) : Event()
    data class ChangeAvatar(val picture: File) : Event()
    }a
    data class ViewModel(
    val stuff: Any?,
    val prefixedName: PrefixedName,
    val avatarUri: Uri
    )b
    class ProfileViewRemix {
    fun onStart() {t
    events
    .compose(presenter)
    .subscribe { viewModel ->
    // rendering view model
    Picasso.get().load(viewModel.avatarUri).into(avatarView)
    }o
    }i
    }t
    

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99. class ProfilePresenter : ObservableTransformer {a
    override fun apply(events: Observable): ObservableSource {d
    return events.flatMap { event ->
    when (event) {y
    is EditName -> appService.setName(event.newName)
    .map { response ->
    when {u
    response.isValid -> NameValid(response.name)
    response.isInvalid -> NameInvalid.also { navigator.goTo(response) }s
    }d
    }f
    .startWith(NameValid(event.newName))
    }g
    }h
    .mergeWith(appService.profile().map(::ProfileResult))
    .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
    BiFunction { previous: ViewModel, result: Result ->
    when (result) {j
    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)
    )f
    }g
    })h
    }j
    }k
    

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100. class ProfilePresenter : ObservableTransformer {a
     override fun apply(events: Observable): ObservableSource {d
     return events.flatMap { event ->
     when (event) {y
     is EditName -> appService.setName(event.newName)
     .map { response ->
     when {u
     response.isValid -> NameValid(response.name)
     response.isInvalid -> NameInvalid.also { navigator.goTo(response) }s
     }d
     }f
     .startWith(NameValid(event.newName))
     }g
     }h
     .mergeWith(appService.profile().map(::ProfileResult))
     .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
     BiFunction { previous: ViewModel, result: Result ->
     when (result) {j
     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)
     )f
     }g
     })h
     }j
     }k
     

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101. class ProfilePresenter : ObservableTransformer {a
     override fun apply(events: Observable): ObservableSource {d
     return events.flatMap { event ->
     when (event) {y
     is EditName -> appService.setName(event.newName)
     .map { response ->
     when {u
     response.isValid -> NameValid(response.name)
     response.isInvalid -> NameInvalid.also { navigator.goTo(response) }s
     }d
     }f
     .startWith(NameValid(event.newName))
     is ChangeAvatar -> appService.changeAvatar(event.picture)
     .map { response -> AvatarValid(response.uri) }
     }g
     }h
     .mergeWith(appService.profile().map(::ProfileResult))
     .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
     BiFunction { previous: ViewModel, result: Result ->
     when (result) {j
     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)
     )f
     }g
     })h
     }j
     }k
     

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102. class ProfilePresenter : ObservableTransformer {a
     override fun apply(events: Observable): ObservableSource {d
     return events.flatMap { event ->
     when (event) {y
     is EditName -> appService.setName(event.newName)
     .map { response ->
     when {u
     response.isValid -> NameValid(response.name)
     response.isInvalid -> NameInvalid.also { navigator.goTo(response) }s
     }d
     }f
     .startWith(NameValid(event.newName))
     is ChangeAvatar -> appService.changeAvatar(event.picture)
     .map { response -> AvatarValid(response.uri) }
     .onErrorReturn { throwable -> AvatarInvalid(throwable) }
     }g
     }h
     .mergeWith(appService.profile().map(::ProfileResult))
     .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
     BiFunction { previous: ViewModel, result: Result ->
     when (result) {j
     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)
     )f
     }g
     })h
     }j
     }k
     

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103. class ProfilePresenter : ObservableTransformer {a
     override fun apply(events: Observable): ObservableSource {d
     return events.flatMap { event ->
     when (event) {y
     is EditName -> appService.setName(event.newName)
     .map { response ->
     when {u
     response.isValid -> NameValid(response.name)
     response.isInvalid -> NameInvalid.also { navigator.goTo(response) }s
     }d
     }f
     .startWith(NameValid(event.newName))
     is ChangeAvatar -> appService.changeAvatar(event.picture)
     .map { response -> AvatarValid(response.uri) }
     .onErrorReturn { throwable -> AvatarInvalid(throwable) }
     }g
     }h
     .mergeWith(appService.profile().map(::ProfileResult))
     .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
     BiFunction { previous: ViewModel, result: Result ->
     when (result) {j
     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)
     )f
     is AvatarValid -> previous.copy(avatarUri = result.uri)
     }g
     })h
     }j
     

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104. override fun apply(events: Observable): ObservableSource {d
     return events.flatMap { event ->
     when (event) {y
     is EditName -> appService.setName(event.newName)
     .map { response ->
     when {u
     response.isValid -> NameValid(response.name)
     response.isInvalid -> NameInvalid.also { navigator.goTo(response) }s
     }d
     }f
     .startWith(NameValid(event.newName))
     is ChangeAvatar -> appService.changeAvatar(event.picture)
     .map { response -> AvatarValid(response.uri) }
     .onErrorReturn { throwable -> AvatarInvalid(throwable) }
     }g
     }h
     .mergeWith(appService.profile().map(::ProfileResult))
     .scan(ViewModel(stuff = null, prefixedName = PrefixedName("", "")),
     BiFunction { previous: ViewModel, result: Result ->
     when (result) {j
     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)
     )f
     is AvatarValid -> previous.copy(avatarUri = result.uri)
     is AvatarInvalid -> TODO()
     }g
     })h
     }j
     

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105. Architecture forced us to separate concerns
     No need to touch existing code
     Easy to test
     Easy to review
     

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106. Gotta Immutate 'em All!
     Unidirectional Data Flow
     Side-Effects Isolation
     

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107. Benoît Quenaudon @oldergod
     Fin
     

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