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Advanced
Model-View-Intent
The Missing Guide
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Kostiantyn Tarasenko Hannes Dorfmann
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class PersonsPresenter : Presenter {
fun loadPersons(){
view?.showLoading(true)
backend.loadPersons({ persons : List →
view?.showLoading(false)
view?.showPersons(persons)
},
{ error: Throwable →
view?.showLoading(false)
view?.showError(error)
})
}
}
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class PersonsPresenter : Presenter {
fun loadPersons(){
view?.showLoading(true)
backend.loadPersons({ persons : List →
view?.showLoading(false)
view?.showPersons(persons)
},
{ error: Throwable →
view?.showLoading(false)
view?.showError(error)
})
}
}
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class PersonsViewModel : ViewModel {
val loading : LiveData
val persons : LiveData>
val error : LiveData
fun loadPersons(){
loading.setValue( true )
backend.loadPersons({ p : List →
loading.setValue( false )
persons.setValue( p )
},
{ e : Throwable →
loading.setValue( false )
error.setValue( e )
})
}
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class PersonsViewModel : ViewModel {
val loading : LiveData
val persons : LiveData>
val error : LiveData
fun loadPersons(){
loading.setValue( true )
backend.loadPersons({ p : List →
loading.setValue( false )
persons.setValue( p )
},
{ e : Throwable →
loading.setValue( false )
error.setValue( e )
})
}
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public TrainingSpotsPresenter(TrainingSpotsMvp.View view, TrainingSpotsMvp.Model model,
NetworkManager networkManager,
FreeleticsTracking tracking,
ScreenTrackingDelegate screenTrackingDelegate,
EventBuildConfigInfo eventBuildConfigInfo) {
this.model = model;
this.view = view;
this.networkManager = networkManager;
this.tracking = tracking;
this.screenTrackingDelegate = screenTrackingDelegate;
this.eventBuildConfigInfo = eventBuildConfigInfo;
subscriptions = new CompositeDisposable();
}
@Override
public void setTrackingScreenName() {
screenTrackingDelegate.setScreenName(tracking, TrainingSpotsEvents.TRAINING_SPOT_LIST_PAGE_ID);
}
@Override
public void loadTrainingSpots() {
if (!networkManager.isOnline()) {
view.showNoInternetConnection();
return;
}
view.showProgress(true);
if (model.hasNoGpsPermissions()) {
loadDefaultTrainingSpots();
} else {
subscriptions.add(model.checkForHighAccuracy()
.subscribe(status -> loadDefaultTrainingSpots(),
throwable -> loadDefaultTrainingSpots(),
() -> subscriptions.add(
model.getNextTrainingSpots()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(trainingSpots -> {
view.showProgress(false);
view.showLocalTrainingSpots(trainingSpots, model.getNearbyTrainingSpotThreshold());
view.showShareNearbyTrainingSpotBanner(
model.shouldShowBanner(trainingSpots));
tracking.trackEvent(
TrainingSpotsEvents
.pageImpressionTrainingSpotsList(
eventBuildConfigInfo,
true,
trainingSpots));
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model.shouldShowBanner(trainingSpots));
tracking.trackEvent(
TrainingSpotsEvents
.pageImpressionTrainingSpotsList(
eventBuildConfigInfo,
true,
trainingSpots));
view.enablePaging(true);
}, throwable -> {
view.showProgress(false);
if (throwable instanceof TimeoutException) {
view.showTimeoutMessage();
} else {
view.showConnectionError();
}
}))));
}
}
private void loadDefaultTrainingSpots() {
subscriptions.add(model.getDefaultTrainingSpots()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(trainingSpots -> {
view.showProgress(false);
view.showDefaultTrainingSpots(trainingSpots);
tracking.trackEvent(TrainingSpotsEvents.pageImpressionTrainingSpotsList(
eventBuildConfigInfo, false, trainingSpots));
view.enablePaging(false);
}, throwable -> {
view.showProgress(false);
view.showConnectionError();
}));
}
@Override
public void loadMoreTrainingSpots() {
if (!networkManager.isOnline()) {
view.showNoInternetConnectionMessage();
view.enablePaging(false);
return;
}
view.showLoadingMoreTrainingSpotsProgress(true);
Disposable disposable = model.getNextTrainingSpots()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(trainingSpots -> {
view.showLoadingMoreTrainingSpotsProgress(false);
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.subscribe(trainingSpots -> {
view.showLoadingMoreTrainingSpotsProgress(false);
view.showMoreLocalTrainingSpots(trainingSpots, model.getNearbyTrainingSpotThreshold());
view.showShareNearbyTrainingSpotBanner(model.shouldShowBanner(trainingSpots));
},
throwable -> {
view.showLoadingMoreTrainingSpotsProgress(false);
view.showConnectionErrorMessage();
view.enablePaging(false);
});
subscriptions.add(disposable);
}
@Override
public void handleTrainingSpotSelection(TrainingSpot trainingSpot) {
tracking.trackEvent(TrainingSpotsEvents.trainingSpotDetails(eventBuildConfigInfo, trainingSpot.id()));
view.showTrainingSpotDetails(model.getLastKnownUserLocation(), trainingSpot);
}
@Override
public void handleShareNearbyTrainingSpotAction() {
view.openShareNearbySpotForm(model.getFormUrl());
}
@Override
public void handleFooterLocationAction() {
if (model.hasNoGpsPermissions()) {
view.showGpsPermissionDialog(GPS_PERMISSIONS_REQUEST_CODE);
} else {
checkForHighAccuracy();
}
}
@Override
public void handleDisclaimerAction() {
view.showDisclaimerPopUp();
}
@Override
public void handleChangeLocationSettingsResult(boolean success) {
if (success) {
if (model.hasNoGpsPermissions()) {
view.showGpsPermissionDialog(GPS_PERMISSIONS_REQUEST_CODE);
} else {
loadTrainingSpots();
}
} else {
view.showEnableHighAccuracyModeErrorDialog();
}
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intent
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intent
state
render (state)
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intent
state
render (state)
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sealed class State {
object Loading : State()
data class Content(val persons : List) : State()
data class Error(val error : Throwable) : State()
}
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https://youtu.be/YGmxbwI3a-4
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intent
state
render (state)
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State Management
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View
ViewModel / Presenter
State Machine
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View
ViewModel / Presenter
State Machine
Intent
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View
ViewModel / Presenter
State Machine
Intent
Input
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View
ViewModel / Presenter
State Machine
Intent
Input State
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View
ViewModel / Presenter
State Machine
Intent
Input State
View State
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Wednesday June 27 2:50 PM - Room Cupcake
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Simple State Machines
val httpRequest : Observable> = ...
val state : Observable = ???
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sealed class State {
object Loading : State()
data class Content(val persons : List) : State()
data class Error(val error : Throwable) : State()
}
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Simple State Machines
val httpRequest : Observable> = ...
val state : Observable = httpRequest
.map { persons → State.Content(persons) }
.onErrorReturn { State.Error(it) }
.startWith(State.Loading)
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Simple State Machines
val httpRequest : Observable> = ...
val state : Observable = httpRequest
.map { persons → State.Content(persons) }
.onErrorReturn { State.Error(it) }
.startWith(State.Loading)
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Simple State Machines
val httpRequest : Observable> = ...
val state : Observable = httpRequest
.map { persons → State.Content(persons) }
.onErrorReturn { State.Error(it) }
.startWith(State.Loading)
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Simple State Machines
val sm1: Observable = …
val sm2: Observable = ...
val combined: Observable = Observable.zip(sm1, sm2){ s1,s2 →
...
})
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Simple State Machines
val sm1: Observable = …
val sm2: Observable = ...
val combined: Observable = Observable.zip(sm1, sm2){ s1,s2 →
if (s1 is State.Error)
s1
...
})
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Simple State Machines
val sm1: Observable = …
val sm2: Observable = ...
val combined: Observable = Observable.zip(sm1, sm2){ s1,s2 →
if (s1 is State.Error)
s1
if (s2 is State.Error)
s2
...
})
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Simple State Machines
val sm1: Observable = …
val sm2: Observable = ...
val combined: Observable = Observable.zip(sm1, sm2){ s1,s2 →
if (s1 is State.Error)
s1
if (s2 is State.Error)
s2
if (s1 == State.Loading || s2 == State.Loading)
State.Loading
...
})
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Simple State Machines
val http1: Observable> = …
val http2: Observable> = ...
val combined: Observable = Observable.zip(http1, http2
){ p1,p2 →
p1 + p2
})
.map { persons → State.Content(persons) }
.onErrorReturn { State.Error(it) }
.startWith(State.Loading)
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Advanced State Machines
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class CalculatorStateMachine {
}
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class CalculatorStateMachine {
sealed class Input {
data class Add(val value: Int) : Input()
data class Sub(val value: Int) : Input()
data class Mul(val value: Int) : Input()
data class Div(val value: Int) : Input()
}
}
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class CalculatorStateMachine {
sealed class Input {
...
}
sealed class State {
data class Result(val value: Int) : State()
data class Error(val error: Throwable) : State()
}
}
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class CalculatorStateMachine {
sealed class Input {
...
}
sealed class State {
...
}
private val inputRelay = PublishRelay.create()
}
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class CalculatorStateMachine {
sealed class Input {
...
}
sealed class State {
...
}
private val inputRelay = PublishRelay.create()
val input : Consumer = inputRelay
}
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class CalculatorStateMachine {
sealed class Input {
...
}
sealed class State {
...
}
private val inputRelay = PublishRelay.create()
val input : Consumer = inputRelay
val state: Observable = inputRelay.map { ... }
}
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class CalculatorStateMachine {
sealed class Input {
...
}
sealed class State {
...
}
private val inputRelay = PublishRelay.create()
val input : Consumer = inputRelay
val state: Observable = inputRelay.map { ... }
}
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State Reducer
.scan(State.Loading) { currentState , input →
// compute new state
…
}
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Fancy Redux Based State Machines
- Store → Observable for State
- Actions as input
- Reducer: (State , Action ) → State
- Isolate Side Effects
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Fancy Redux Based State Machines
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Tuesday June 26 11:05 AM - Room Lollipop
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Tuesday June 26 11:05 AM - Room Oreo
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Intent? Action?
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View
ViewModel / Presenter
State Machine
Intent
Intent State
View State
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View
ViewModel / Presenter
State Machine
Intent
Intent State
View State
.scan( )
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View
ViewModel / Presenter
Redux State Machine
Intent
Action State
View State
Action
triggered by side effect
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View
Redux State Machine
reducer(state, action) : State nextPage(nextPageAction) : Action
State
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View
Redux State Machine
reducer(state, action) : State nextPage(nextPageAction) : Action
State
Next page
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View
Redux State Machine
reducer(state, action) : State nextPage(nextPageAction) : Action
State
Next page
Next page
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View
Redux State Machine
reducer(state, action) : State nextPage(nextPageAction) : Action
State
Next page
Next page
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View
Redux State Machine
reducer(state, action) : State nextPage(nextPageAction) : Action
State
Next page
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View
Redux State Machine
reducer(state, action) : State nextPage(nextPageAction) : Action
State
LoadingPage
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View
Redux State Machine
reducer(state, action) : State nextPage(nextPageAction) : Action
State
LoadingPage
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View
Redux State Machine
reducer(state, action) : State nextPage(nextPageAction) : Action
State
LoadingPage
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View
Redux State Machine
reducer(state, action) : State nextPage(nextPageAction) : Action
State
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View
Redux State Machine
reducer(state, action) : State nextPage(nextPageAction) : Action
State
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View
Redux State Machine
reducer(state, action) : State nextPage(nextPageAction) : Action
State
ResultNextPage
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View
Redux State Machine
reducer(state, action) : State nextPage(nextPageAction) : Action
State
ResultNextPage
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View
Redux State Machine
reducer(state, action) : State nextPage(nextPageAction) : Action
State
ResultNextPage
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View
Redux State Machine
reducer(state, action) : State nextPage(nextPageAction) : Action
State
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View
Redux State Machine
reducer(state, action) : State Side Effect 1
State
Side Effect 2
Side Effect n
...
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val sideEffects = listOf< SideEffect >(
...
nextPageSideEffect,
pullToRefreshSideEffect,
...
)
intents
.reduxStore(initialState, sideEffects, reducer)
.subscribe { state → view.render(state) }
https://github.com/freeletics/RxRedux
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Testing
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Testing is easy
- assert(expectedState, actualState)
- Just trigger intent, wait for state change
- No need for idling resource needed
- Prefer integration testing over unit testing
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class MyActivity : Activity() {
override fun onCreate(savedInstanceState: Bundle?) {
...
val button = findViewById(R.id.button)
...
}
fun render(state: State) {
...
}
}
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class MyActivity : Activity() {
@Inject lateinit var binding : ViewBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
// inject binding
...
}
fun render(state: State) {
binding.render()
}
}
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class ViewBinding(val rootView : View) {
val button = rootView.findViewById(R.id.button)
fun render(state: State) {
...
}
}
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class TestingViewBinding(rootView : View) : ViewBinding {
val renderdStates : Observable = replay
private val replay = ReplayRelay.create()
override fun render(state: State) {
super.render(state)
replay.onNext(state)
Screenshot.snap(rootView).record()
}
}
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class TestingViewBinding(rootView : View) : ViewBinding {
val renderdStates : Observable = replay
private val replay = ReplayRelay.create()
override fun render(state: State) {
super.render(state)
replay.onNext(state)
Screenshot.snap(rootView).record()
}
}
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class TestingViewBinding(rootView : View) : ViewBinding {
val renderdStates : Observable = replay
private val replay = ReplayRelay.create()
override fun render(state: State) {
super.render(state)
replay.onNext(state)
Screenshot.snap(rootView).record()
}
}
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class TestingViewBinding(rootView : View) : ViewBinding {
val renderdStates : Observable = replay
private val replay = ReplayRelay.create()
override fun render(state: State) {
super.render(state)
replay.onNext(state)
Screenshot.snap(rootView).record()
}
}
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class TestingViewBinding(rootView : View) : ViewBinding {
val renderdStates : Observable = replay
private val replay = ReplayRelay.create()
override fun render(state: State) {
super.render(state)
replay.onNext(state)
Screenshot.snap(rootView).record()
}
}
https://facebook.github.io/screenshot-tests-for-android/
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Tracking
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Multicasting
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RxJava By Example - Vol 3. the Multicast Edition
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intents
.share()
.subscribe { intent ->
when (intent) {
NextButtonClick -> tracker.trackNextButtonClick()
...
}
}
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stateMachine
.share()
.subscribe { state ->
when (state) {
is StateA -> tracker.trackStateA()
...
}
}
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Navigation
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sealed class State {
data class UserData(
val login: String,
val password: String
) : State()
data class SingingIn(
val login: String,
val password: String
) : State()
data class Error(
val login: String,
val password: String,
val errorMessage: String,
) : State()
object SignedIn : State()
}
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sealed class State {
data class UserData(
val login: String,
val password: String
) : State()
data class SingingIn(
val login: String,
val password: String
) : State()
data class Error(
val login: String,
val password: String,
val errorMessage: String,
) : State()
object SignedIn : State(
}
fun render(state: State) {
when (state) {
State.SignedIn -> {
startActivity(nextActivityIntent())
finish()
}
...
}
}
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Navigator
stateMachine
.share()
.subscribe { state ->
when (state) {
... -> navigator.navigateTo(Destination.OptionalQuestions)
}
}
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Navigator
stateMachine
.share()
.subscribe { state ->
when (state) {
... -> navigator.navigateTo(Destination.OptionalQuestions)
}
}
class WizardNavigator(
private val activity: Activity,
private val abTestProvider: AbTestProvider
) : Navigator {
override fun navigateTo(dest: Destination) {
when (dest) {
Destination.Form -> showFormFragment()
Destination.OptionalQuestions -> showOptionalQuestionsFragment()
Destination.VariantSelector -> showVariantSelectorFragment()
Destination.FromSaved -> activity.startActivity(abTestProvider.nextScreen())
}
}
}
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Navigator implementation
Deep inside, the Navigator implementation could be as simple as
override fun navigateTo(dest: Destination) {
when (dest) {
Destination.Next -> showNextActivity()
...
}
}
fun showNextActivity() {
activity.startActivity(
if (FeatureFlag.A) {
activityOneIntent()
} else {
activityTwoIntent()
}
)
}
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Navigator implementation
Or be little bit modern
override fun navigateTo(dest: Destination) {
when (dest) {
Destination.Next -> showNextActivity()
...
}
}
fun showNextActivity() {
view.findNavController().navigate(R.id.wizard_next_activity)
}
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Animation
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Animation
private sealed class InternalAnimationState {
object InitialState : InternalAnimationState()
object ProgressTransition : InternalAnimationState()
data class Progress(
val textResId: Int,
val currentProgressPercent: Int,
val totalProgressDuration: Long
) : InternalAnimationState()
object GenerationFinished : InternalAnimationState()
}
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Animation
object InitialState :InternalAnimationState()
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Animation
object ProgressTransition
:InternalAnimationState()
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Animation
data class Progress(
val textResId: Int,
val currentProgressPercent: Int,
val totalProgressDuration: Long
) :InternalAnimationState()
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Animation
object GenerationFinished :InternalAnimationState()
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Animation
private fun createAnimationStateObservable(): Observable =
Observable.merge(
intents.filter { it == GenerationClicked }
.map { ProgressTransition },
intents.filter { it == GenerationStarted }
.flatMap {
Observable.intervalRange(
0, steps, 0,
duration / steps, TimeUnit.MILLISECONDS
).map { it.toInt() }
.map {
if (step == size) {
GenerationFinished
} else {
Progress(...)
}
}
})
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Animation
private fun createAnimationState(): Observable = rxObservable {
intents.consumeEach { intent ->
when (intent) {
GenerationClicked -> send(ProgressTransition)
GenerationStarted -> {
repeat(size) { step ->
delay(duration / size)
send(if (step == texts.size) {
GenerationFinished
} else {
Progress(...)
})
}
}
}
}
}
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Animation
private fun createAnimationState(): Observable = rxObservable {
intentStream.consumeEach { intent ->
when (intent) {
GenerationClicked -> send(ProgressTransition)
GenerationStarted -> {
repeat(size) { step ->
delay(duration / size)
send(if (step == texts.size) {
GenerationFinished
} else {
Progress(...)
})
}
}
}
}
}
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Restoring state
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enum class Variant {
Variant1, Variant2
}
data class Step1State(
val selected: Variant
)
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enum class Variant {
Variant1, Variant2
}
data class Step1State(
val selected: Variant
)
data class Step2State(
val option1Checked: Boolean,
val option2Checked: Boolean
)
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enum class Variant {
Variant1, Variant2
}
data class Step1State(
val selected: Variant
)
data class Step2State(
val option1Checked: Boolean,
val option2Checked: Boolean
)
data class Step3State(
val name : String,
val description : String
)
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data class WizardState(
val currentScreenIndex: Int,
val step1State: Step1State,
val step2State: Step2State,
val step3State: Step3State
)
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Tips and tricks
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How to handle onActivityResult?
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onRequestPermissionResult()?
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What about Lifecycle callback?
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Rendering state too fast?
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How to refactor existing code
to MVI?
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Refactoring
1. Define States
2. MVP: replace all view.showX() → view.render(state)
MVVM: replace all LiveData → LiveData
3. Define a state machine with a clear API
Inputs and Outputs
4. Define Intents that trigger inputs on state machine
5. Trigger Intents from view layer
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Questions?
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Links
- The State of Representing State by Christina Lee
- RxJava By Example - Vol 3. the Multicast Edition by Kaushik Gopal
- Screenshot testing: https://facebook.github.io/screenshot-tests-for-android/
- https://github.com/freeletics/RxRedux