Riding the State Flow

View, State, Action ... Unidirectional Data Flow is not a concept unique to React. Used for many years in Web development, it tends to propagate to mobile platforms. Why? Because it helps develop our UI and consider the changes as states and events.

This topic is not new on Android. But Kotlin and coroutines can now greatly improve our experience.

Let's see how we can structure our Android MVVM development with such an approach. Let's take some concrete samples and see how we can easily write it with just a Kotlin function, and even embrace functional programming.

Transcript

2. Riding the State Flow AndroidMakers
3. ! Software Eng @ BlaBlaCar Mobile First Kotlin Open Source Arnaud GIULIANI
5. Building mobile applications…
6. View Model Presenter ViewModel …
7. business logic & data layers (database, networking…) Model Presenter ViewModel … Request data to Model and prepare it for UI
8. Why are we still having issues with MVP, MVVM?
9. View, State, Action … … to help us solve them
10. MVP
11. View: display data, notified by the presenter & notify for actions Presenter: manage UI logic, data & interactions View Presenter 1 .. 1 - Contract MVP
12. Problems with MVP ⚠
13. Tight coupling logic View/Presenter Data inconsistency Not reactive approach?
14. MVVM
15. View: observe streams to display data & uses actions ViewModel: exposes actions & expose streams of data View ViewModel actions data MVVM
16. From MVP to MVVM
18. Architecture Components Lifecycle ViewModel LiveData
19. Just use streams, what else?
20. Still got some problems ⚠
21. View & business logic coupling Data streams inconsistency
22. Why is it hard to write? UI binding with incomplete data? Bad separation of concerns? is MVVM less formal?
24. Let’s think states over interactions
25. Unidirectional data flow ♻
26. •- the state change is passed to the view •- actions can update the state •- actions are triggered by the view •- state is passed to the view * aka Redux
27. Single source of truth Immutable data Testability, Logging & Replayability
28. Redux-ing UI bugs - Christina Lee @RunChristinaRun
29. MVI - Mosby http:/ /hannesdorfmann.com/mosby/
30. @dggonzalez
31. @dggonzalez
32. <Store> <Reducer> <VM Dispatcher>
33. …well
34. View ViewModel Trigger action Dispatch action Action Reducer State Store Run action & get new state Apply & Store new state Notify new state Notify state
35. View ViewModel Trigger action Dispatch action Action Reducer State Store Run action & Got event No state Notify new event Notify event
36. Can we avoid to write Reducer & Store?
37. Just focus on writing Actions?
38. ViewModel Event State View action State - UI State (Main Data) Event - Side events
39. ViewModel offers Actions
40. Action emits States
41. Testing—action’s sequence of states & events
42. Coroutines inside ✅
43. Simplify Async Code
44. View ViewModel Trigger action Dispatch action Action Reducer State Store Run action on current state (Actor & FlowAction) Apply & Store new state (LiveData) Notify new state Notify state
45. View AndroidDataFlow Trigger action Dispatch action Action Reducer State Store Run action on current state (Actor & FlowAction) Apply & Store new state (LiveData) Notify new state Notify state Provided by Uniflow
46. Let’s go
47. #1 - A simple “Action”
48. #1 - A simple “Action”
49. Day Weather Icon Weather Description Temperature Humidity Wind
50. Day Weather Icon Weather Description Temperature Humidity Wind Empty WeatherDetail
51. Immutable Data
52. object class Empty() data class WeatherDetail(val day: String, val icon: String, val description: String, val wind: String, val temperature: String, val humidity: String)
53. object class Empty() : UIState() data class WeatherDetail(val day: String, val icon: String, val description: String, val wind: String, val temperature: String, val humidity: String) : UIState()
54. sealed class GetWeatherState : UIState(){ object class Empty() : GetWeatherState() data class WeatherDetail(val day: String, val icon: String, val description: String, val wind: String, val temperature: String, val humidity: String) : GetWeatherState() }
55. sealed class GetWeatherState : UIState(){ object class Empty() : GetWeatherState() data class WeatherDetail(val day: String, val icon: String, val description: String, val wind: String, val temperature: String, val humidity: String) : GetWeatherState() }
56. ViewModel
57. class WeatherDetailViewModel( ) : ViewModel() { }
58. class WeatherDetailViewModel( ) : ViewModel() { }
59. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : ViewModel() { }
60. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : ViewModel() { fun getDetail() { } }
61. Action as function
62. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : ViewModel() { fun getDetail() { } }
63. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() { } } UDF ViewModel
64. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { } }
65. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { } } Emit states & events ♻
66. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { } } Run coroutines on IO ⚡
67. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { currentState : UIState -> } } Run on current state ♻
68. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { val dailyForecast = repo.getDailyForecast(id) setState { dailyForecast.mapToWeatherState() } } }
69. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { val dailyForecast = repo.getDailyForecast(id) setState { dailyForecast.mapToWeatherState() } } } async call ⚡
70. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { val dailyForecast = repo.getDailyForecast(id) setState { dailyForecast.mapToWeatherState() } } }
71. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { val dailyForecast = repo.getDailyForecast(id) setState { dailyForecast.mapToWeatherState() } } } emit new state ♻
72. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { val dailyForecast = repo.getDailyForecast(id) setState { dailyForecast.mapToWeatherState() } } }
73. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { val dailyForecast = repo.getDailyForecast(id) setState { dailyForecast.mapToWeatherState() } } } fun DailyForecast.mapToWeatherState() = WeatherDetail(...)
74. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { val dailyForecast = repo.getDailyForecast(id) setState { dailyForecast.mapToWeatherState() } } }
75. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow(defaultState = Empty) { fun getDetail() = action { val dailyForecast = repo.getDailyForecast(id) setState { dailyForecast.mapToWeatherState() } } }
76. Error Handling
77. object class Empty() : UIState() data class Failed(val message: String, val error: Exception) : UIState() data class WeatherDetail(val day: String, val icon: String, val description: String, val wind: String, val temperature: String, val humidity: String) : UIState()
78. object class Empty() : UIState() data class Failed(val message: String, val error: Exception) : UIState() data class WeatherDetail(val day: String, val icon: String, val description: String, val wind: String, val temperature: String, val humidity: String) : UIState()
79. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { val dailyForecast = repo.getDailyForecast(id) setState { dailyForecast.mapToWeatherState() } } }
80. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { try { val dailyForecast = repo.getDailyForecast(id) setState { dailyForecast.mapToWeatherState() } } catch (error: Exception) { setState { Failed(“got error”, error) } } } }
81. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { val dailyForecast = repo.getDailyForecast(id) setState { dailyForecast.mapToWeatherState() } } }
82. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action( onAction = { val dailyForecast = repo.getDailyForecast(id) setState { dailyForecast.mapToWeatherState() } } ) }
83. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action( onAction = { val dailyForecast = repo.getDailyForecast(id) setState { dailyForecast.mapToWeatherState() } }, onError = { error , state -> setState { Failed("got error", error) } } ) }
84. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action( onAction = { val dailyForecast = repo.getDailyForecast(id) setState { dailyForecast.mapToWeatherState() } }, onError = { error , state -> setState { Failed("got error", error) } } ) }
85. UI Binding
86. class WeatherDetailActivity : AppCompatActivity() { private val detailViewModel: DetailViewModel by viewModel() override fun onCreate(savedInstanceState: Bundle?) { //... onStates(detailViewModel) { state -> when (state) { is Empty -> {} // do nothing is WeatherDetail -> showDetail(state) is Failed -> showError(state.error) } } detailViewModel.getDetail() }
87. class WeatherDetailActivity : AppCompatActivity() { private val detailViewModel: DetailViewModel by viewModel() override fun onCreate(savedInstanceState: Bundle?) { //... onStates(detailViewModel) { state -> when (state) { is Empty -> {} // do nothing is WeatherDetail -> showDetail(state) is Failed -> showError(state.error) } } detailViewModel.getDetail() }
88. class WeatherDetailActivity : AppCompatActivity() { private val detailViewModel: DetailViewModel by viewModel() override fun onCreate(savedInstanceState: Bundle?) { //... onStates(detailViewModel) { state -> when (state) { is Empty -> {} // do nothing is WeatherDetail -> showDetail(state) is Failed -> showError(state.error) } } detailViewModel.getDetail() }
89. class WeatherDetailActivity : AppCompatActivity() { private val detailViewModel: DetailViewModel by viewModel() override fun onCreate(savedInstanceState: Bundle?) { //... onStates(detailViewModel) { state -> when (state) { is Empty -> {} // do nothing is WeatherDetail -> showDetail(state) is Failed -> showError(state.error) } } detailViewModel.getDetail() }
90. class WeatherDetailActivity : AppCompatActivity() { private val detailViewModel: DetailViewModel by viewModel() override fun onCreate(savedInstanceState: Bundle?) { //... onStates(detailViewModel) { state -> when (state) { is Empty -> {} // do nothing is WeatherDetail -> showDetail(state) is Failed -> showError(state.error) } } detailViewModel.getDetail() }
91. class WeatherDetailActivity : AppCompatActivity() { private val detailViewModel: DetailViewModel by viewModel() override fun onCreate(savedInstanceState: Bundle?) { //... onStates(detailViewModel) { state -> when (state) { is Empty -> {} // do nothing is WeatherDetail -> showDetail(state) is Failed -> showError(state.error) } } detailViewModel.getDetail() }
92. class WeatherDetailActivity : AppCompatActivity() { private val detailViewModel: DetailViewModel by viewModel() override fun onCreate(savedInstanceState: Bundle?) { //... onEvents(detailViewModel) { event -> when (event) { } } detailViewModel.getDetail() }
93. Testing
94. @Test fun `get a daily forecast`() { // prepare detailViewModel = DetailViewModel(id, repo) view = detailViewModel.mockObservers() // mocks val weather = MockedData.dailyForecasts.first() coEvery { repo.getDailyForecast(id) } returns weather // call detailViewModel.getDetail() // sequence of states & events verifySequence { view.states.onChanged(UIState.Empty) view.states.onChanged(weather.mapToDetailState()) } }
95. @Test fun `get a daily forecast`() { // prepare detailViewModel = DetailViewModel(id, repo) view = detailViewModel.mockObservers() // mocks val weather = MockedData.dailyForecasts.first() coEvery { repo.getDailyForecast(id) } returns weather // call detailViewModel.getDetail() // sequence of states & events verifySequence { view.states.onChanged(UIState.Empty) view.states.onChanged(weather.mapToDetailState()) } }
96. @Test fun `get a daily forecast`() { // prepare detailViewModel = DetailViewModel(id, repo) view = detailViewModel.mockObservers() // mocks val weather = MockedData.dailyForecasts.first() coEvery { repo.getDailyForecast(id) } returns weather // call detailViewModel.getDetail() // sequence of states & events verifySequence { view.states.onChanged(UIState.Empty) view.states.onChanged(weather.mapToDetailState()) } }
97. @Test fun `get a daily forecast`() { // prepare detailViewModel = DetailViewModel(id, repo) view = detailViewModel.mockObservers() // mocks val weather = MockedData.dailyForecasts.first() coEvery { repo.getDailyForecast(id) } returns weather // call detailViewModel.getDetail() // sequence of states & events verifySequence { view.states.onChanged(UIState.Empty) view.states.onChanged(weather.mapToDetailState()) } }
98. @Test fun `get a daily forecast`() { // prepare detailViewModel = DetailViewModel(id, repo) view = detailViewModel.mockObservers() // mocks val weather = MockedData.dailyForecasts.first() coEvery { repo.getDailyForecast(id) } returns weather // call detailViewModel.getDetail() // sequence of states & events verifySequence { view.states.onChanged(UIState.Empty) view.states.onChanged(weather.mapToDetailState()) } }
99. @Test fun `get a daily forecast`() { // prepare detailViewModel = DetailViewModel(id, repo) view = detailViewModel.mockObservers() // mocks val weather = MockedData.dailyForecasts.first() coEvery { repo.getDailyForecast(id) } returns weather // call detailViewModel.getDetail() // sequence of states & events verifySequence { view.states.onChanged(Empty) view.states.onChanged(weather.mapToDetailState()) } }
100. One Coding Convention
101. fun myAction() = action { }
102. View AndroidDataFlow Trigger action Dispatch action Action Reducer State Store Run action on current state (Actor & FlowAction) Apply & Store new state (LiveData) Notify new state Notify state Provided by Uniflow
103. #2 - State Guard
104. #2 - State Guard
106. NoSuggestion NewSuggestions The user has no company or n/a The user can select a company (can’t select anything) (select an existing or provide a new one)
107. One View - Multiple States
109. sealed class SelectCompanyState : UIState() { object Empty : SelectCompanyState() data class CompanyList(val list: List<CompanyItem>) : SelectCompanyState() data class CompanySelected(val selectedCompany: CompanyItem) : SelectCompanyState() object NoCompanySelected : SelectCompanyState() }
110. sealed class SelectCompanyState : UIState() { object Empty : SelectCompanyState() data class CompanyList(val list: List<CompanyItem>) : SelectCompanyState() data class CompanySelected(val selectedCompany: CompanyItem) : SelectCompanyState() object NoCompanySelected : SelectCompanyState() }
111. sealed class SelectCompanyState : UIState() { object Empty : SelectCompanyState() data class CompanyList(val list: List<CompanyItem>) : SelectCompanyState() data class CompanySelected(val selectedCompany: CompanyItem) : SelectCompanyState() object NoCompanySelected : SelectCompanyState() }
112. sealed class SelectCompanyState : UIState() { object Empty : SelectCompanyState() data class CompanyList(val list: List<CompanyItem>) : SelectCompanyState() data class CompanySelected(val selectedCompany: CompanyItem) : SelectCompanyState() object NoCompanySelected : SelectCompanyState() }
113. sealed class SelectCompanyState : UIState() { object Empty : SelectCompanyState() data class CompanyList(val list: List<CompanyItem>) : SelectCompanyState() data class CompanySelected(val selectedCompany: CompanyItem) : SelectCompanyState() object NoCompanySelected : SelectCompanyState() }
114. class SelectCompanyViewModel( private val repo: CompanySelectionRepository ) : AndroidDataFlow(defaultState = Empty) { // Search for campanies fun searchForName(name: String) = action { // look for new suggestions ... val suggestions = repo.searchForName(name) setState { CompanyList(suggestions.mapToItems()) } } // Select No Company fun selectNoCompany() = singleActionOn<Empty> { repo.setNoCompany() setState { NoCompanySelected } } // Select a Company fun selectCompany(item: CompanyItem) = singleActionOn<CompanyList> {
115. class SelectCompanyViewModel( private val repo: CompanySelectionRepository ) : AndroidDataFlow(defaultState = Empty) { // Search for campanies fun searchForName(name: String) = action { // look for new suggestions ... val suggestions = repo.searchForName(name) setState { CompanyList(suggestions.mapToItems()) } } // Select No Company fun selectNoCompany() = singleActionOn<Empty> { repo.setNoCompany() setState { NoCompanySelected } } // Select a Company fun selectCompany(item: CompanyItem) = singleActionOn<CompanyList> {
116. class SelectCompanyViewModel( private val repo: CompanySelectionRepository ) : AndroidDataFlow(defaultState = Empty) { // Search for campanies fun searchForName(name: String) = action { // look for new suggestions ... val suggestions = repo.searchForName(name) setState { CompanyList(suggestions.mapToItems()) } } // Select No Company fun selectNoCompany() = singleActionOn<Empty> { repo.setNoCompany() setState { NoCompanySelected } } // Select a Company fun selectCompany(item: CompanyItem) = singleActionOn<CompanyList> {
117. class SelectCompanyViewModel( private val repo: CompanySelectionRepository ) : AndroidDataFlow(defaultState = Empty) { // Search for campanies fun searchForName(name: String) = action { // look for new suggestions ... val suggestions = repo.searchForName(name) setState { CompanyList(suggestions.mapToItems()) } } // Select No Company fun selectNoCompany() = singleActionOn<Empty> { repo.setNoCompany() setState { NoCompanySelected } } // Select a Company fun selectCompany(item: CompanyItem) = singleActionOn<CompanyList> {
118. ) : AndroidDataFlow(default state = Empty) { // Search for campanies fun searchForName(name: String) = action { // look for new suggestions ... val suggestions = repo.searchForName(name) setState { CompanyList(suggestions.mapToItems()) } } // Select No Company fun selectNoCompany() = actionOn<Empty> { repo.setNoCompany() setState { NoCompanySelected } } // Select a Company fun selectCompany(item: CompanyItem) = actionOn<CompanyList> { repo.setCompany()(item) setState { CompanySelected(item) } }
119. ) : AndroidDataFlow(default state = Empty) { // Search for campanies fun searchForName(name: String) = action { // look for new suggestions ... val suggestions = repo.searchForName(name) setState { CompanyList(suggestions.mapToItems()) } } // Select No Company fun selectNoCompany() = actionOn<Empty> { repo.setNoCompany() setState { NoCompanySelected } } // Select a Company fun selectCompany(item: CompanyItem) = actionOn<CompanyList> { repo.setCompany()(item) setState { CompanySelected(item) } } Guard on state <Empty>
120. ) : AndroidDataFlow(default state = Empty) { // Search for campanies fun searchForName(name: String) = action { // look for new suggestions ... val suggestions = repo.searchForName(name) setState { CompanyList(suggestions.mapToItems()) } } // Select No Company fun selectNoCompany() = actionOn<Empty> { currentState: Empty -> repo.setNoCompany() setState { NoCompanySelected } } // Select a Company fun selectCompany(item: CompanyItem) = actionOn<CompanyList> { repo.setCompany()(item) setState { CompanySelected(item) } } current state is <Empty>
121. val suggestions = repo.searchForName(name) setState { CompanyList(suggestions.mapToItems()) } } // Select No Company fun selectNoCompany() = actionOn<Empty> { repo.setNoCompany() setState { NoCompanySelected } } // Select a Company fun selectCompany(item: CompanyItem) = actionOn<CompanyList> { repo.setCompany(item) setState { CompanySelected(item) } }
122. val suggestions = repo.searchForName(name) setState { CompanyList(suggestions.mapToItems()) } } // Select No Company fun selectNoCompany() = actionOn<Empty> { repo.setNoCompany() setState { NoCompanySelected } } // Select a Company fun selectCompany(item: CompanyItem) = actionOn<CompanyList> { repo.setCompany(item) setState { CompanySelected(item) } } Guard on state <CompanyList>
123. View ViewModel Trigger action Dispatch action Action Reducer State Store Run action on current state State is Wrong. Notify with BadOrWrongState event Notify BoW Notify BoW
124. @Test fun `select a company`() { // mock ... viewModel = SelectCompanyViewModel(repo) // call viewModel.selectCompany(mockItem) // sequence of states & events verifySequence { view.states.onChanged(Empty) view.events.onChanged(BadOrWrongState(state = Empty)) } }
125. @Test fun `select a company`() { // mock ... viewModel = SelectCompanyViewModel(repo) // call viewModel.selectCompany(mockItem) // sequence of states & events verifySequence { view.states.onChanged(Empty) view.events.onChanged(BadOrWrongState(state = Empty)) } }
126. NoSuggestion NewSuggestions
127. #3 - Rooting States & Views
128. Activity -> View rooting Shared ViewModel - ViewModelStoreOwner
129. One stream -> Multiple Views
131. WeatherActivity WeatherHeader Fragment WeatherList Fragment ViewModel Weather State Create Create Weather State Weather State ⚠ no arg passed
132. onStates(viewModel) { state -> when (state) { is Loading -> { // show loading animation } is WeatherState -> { // create Fragments } is Failed -> { // display error } } } viewModel.getWeather() <Activity> onStates(viewModel) { state -> when (state) { is WeatherState -> { // display data } } } <Fragment>
133. One stream -> Multiple Views*
135. NewCardActivity NewCardViewModel StartFragment Start State Start State
136. NewCardActivity NewCardViewModel EditCardFragment EditCard State EditCard State
137. NewCardActivity NewCardViewModel VerifyCardFragment VerifyCard State VerifyCard State
138. NewCardActivity NewCardViewModel CheckedCardFragment CheckedCard State CheckedCard State
139. onStates(viewModel) { state -> when (state) { is StartState -> openFragment<StartFragment>() is EditCardState -> openFragment<EditCardFragment>() is VerifyCardState -> openFragment<VerifyCardFragment>() is CheckedCardState -> openFragment<CheckedCardFragment>() } } viewModel.startAddCardFlow() <Activity> onStates(viewModel) { state -> when (state) { is <ViewState> -> { // display data } } } <Fragment>
140. #4 - Safe & Functional
142. Better Unsafe Values Handling With Arrow.io
143. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { val dailyForecast = repo.getDailyForecast(id) setState { dailyForecast.mapToWeatherState() } } }
144. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { val dailyForecast = repo.getDailyForecast(id) setState { dailyForecast.mapToWeatherState() } } }
145. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { val safeState = Either.catch { repo.getDailyForecast(id) } .map { it.mapToWeatherState() } .getOrHandle { error -> Failed(“got error", error) } setState { safeState } } }
146. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { val safeState = Either.catch { repo.getDailyForecast(id) } .map { it.mapToWeatherState() } .getOrHandle { error -> Failed(“got error", error) } setState { safeState } } }
147. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { val safeState = Either.catch { repo.getDailyForecast(id) } .map { it.mapToWeatherState() } .getOrHandle { error -> Failed("got error", error) } setState { safeState } } }
148. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { val safeState = Either.catch { repo.getDailyForecast(id) } .map { it.mapToWeatherState() } .getOrHandle { error -> Failed(“got error", error) } setState { safeState } } }
149. class WeatherDetailViewModel( private val id: DailyForecastId, private val repo: WeatherRepository ) : AndroidDataFlow() { fun getDetail() = action { val safeState = Either.catch { repo.getDailyForecast(id) } .map { it.mapToWeatherState() } .getOrHandle { error -> Failed(“got error", error) } setState { safeState } } }
150. Ready to ride the State Flow?
151. Make your own Experience
152. Think UI as States
153. Unidirectional Data Flow
154. Architecture — Decisions which are both important and hard to change Martin Fowler
155. One way of thinking But many ways to write it
156. ~5 classes
157. Uniflow https:/ /github.com/uniflow-kt/
158. Arnaud Giuliani @arnogiu Thank you!
159. Any question? 3 sli.do