Reactive StateManagement with Model-View-Intent

mobiconf 2017, Krakow

Managing application state is not a simple topic especially on Android with a synchronous and asynchronous source of data, components having different lifecycles, back stack navigation and process death.

Model-View-Intent (MVI) is an architectural design pattern to separate the View from the Model. In this talk, we will discuss the idea behind MVI and how this pattern compares to other architectural patterns like Flux, Redux, Model-View-Presenter or Model-View-ViewModel. Furthermore, we will discuss what a Model actually is and how Model is related to State.

Once we have understood the role of Model and State we will focus on state management by building an unidirectional data flow.

Finally, we will connect the dots with RxJava to build apps with deterministic state management in a reactive way that makes maintaining and testing such apps easy.

Transcript

2. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 Rainer Weiss Kip Thorne Barry Barish
3. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 Rainer Weiss Kip Thorne Barry Barish Nobel laureates in Physics 2017 Gravitational waves
4. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 General relativity
5. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017
6. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 a thousand part of a proton
7. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 2 black holes melded 1.3 Billion years ago Gravitational waves detected
8. 8 REACTIVE STATEMANAGEMENT WITH MODEL-VIEW-INTENT
9. 9 HELLO I’M HANNES
10. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 MVP MVC MVVM MVC MVI
11. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 MVP MVC MVVM MVI
12. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 What is a Model?
13. class PersonsPresenter : Presenter<PersonsView> { fun loadPersons() { view?.showLoading(true) backend.loadPersons({ persons : List<Person> -> view?.showPersons(persons) }, { error: Throwable -> view?.showError(error) }) } }
14. class PersonsPresenter : Presenter<PersonsView> { fun loadPersons() { view?.showLoading(true) backend.loadPersons({ persons : List<Person> -> view?.showPersons(persons) }, { error: Throwable -> view?.showError(error) }) } }
15. class PersonsPresenter : Presenter<PersonsView> { fun loadPersons(){ view?.showLoading(true) backend.loadPersons({ persons : List<Person> -> view?.showPersons(persons) }, { error: Throwable -> view?.showError(error) }) } }
16. class PersonsPresenter : Presenter<PersonsView> { fun loadPersons(){ view?.showLoading(true) backend.loadPersons({ persons : List<Person> -> view?.showPersons(persons) }, { error: Throwable -> view?.showError(error) }) } }
17. class PersonsPresenter : Presenter<PersonsView> { fun loadPersons(){ view?.showLoading(true) backend.loadPersons({ persons : List<Person> -> view?.showPersons(persons) }, { error: Throwable -> view?.showError(error) }) } }
18. class PersonsPresenter : Presenter<PersonsView> { fun loadPersons(){ view?.showLoading(true) // Displays a ProgressBar backend.loadPersons({ persons : List<Person> -> view?.showPersons(persons) // Displays a ProgressBar }, { error: Throwable -> view?.showError(error) // Displays a error message }) } }
19. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 What is a Model?
20. class PersonsViewModel : ViewModel { val loadingLiveData : MutableLiveData<Boolean> … fun loadPersons(){ loadingLiveData.setValue((true) backend.loadPersons({ persons : List<Person> -> loadingLiveData.setValue( false ) personsLiveData.setValue( persons ) }, { error: Throwable -> loadingLiveData.setValue( false ) errorLiveData.setValue( error ) }) } }
21. class PersonsViewModel : ViewModel { val loadingLiveData : MutableLiveData<Boolean> … fun loadPersons(){ loadingLiveData.setValue((true) backend.loadPersons({ persons : List<Person> -> loadingLiveData.setValue( false ) personsLiveData.setValue( persons ) }, { error: Throwable -> loadingLiveData.setValue( false ) errorLiveData.setValue( error ) }) } }
22. class PersonsViewModel : ViewModel { val loadingLiveData : MutableLiveData<Boolean> … fun loadPersons(){ loadingLiveData.setValue((true) backend.loadPersons({ persons : List<Person> -> loadingLiveData.setValue( false ) personsLiveData.setValue( persons ) }, { error: Throwable -> loadingLiveData.setValue( false ) errorLiveData.setValue( error ) }) } }
23. class PersonsViewModel : ViewModel { val loadingLiveData : MutableLiveData<Boolean> … fun loadPersons(){ loadingLiveData.setValue((true) backend.loadPersons({ persons : List<Person> -> loadingLiveData.setValue( false ) personsLiveData.setValue( persons ) }, { error: Throwable -> loadingLiveData.setValue( false ) errorLiveData.setValue( error ) }) } }
24. class PersonsViewModel : ViewModel { val loadingLiveData : MutableLiveData<Boolean> … fun loadPersons(){ loadingLiveData.setValue((true) backend.loadPersons({ persons : List<Person> -> loadingLiveData.setValue( false ) personsLiveData.setValue( persons ) }, { error: Throwable -> loadingLiveData.setValue( false ) errorLiveData.setValue( error ) }) } }
25. class PersonsViewModel : ViewModel { val loadingLiveData : MutableLiveData<Boolean> … fun loadPersons(){ loadingLiveData.setValue((true) backend.loadPersons({ persons : List<Person> -> loadingLiveData.setValue( false ) personsLiveData.setValue( persons ) }, { error: Throwable -> loadingLiveData.setValue( false ) errorLiveData.setValue( error ) }) } }
26. class PersonsViewModel : ViewModel { val loadingLiveData : MutableLiveData<Boolean> … fun loadPersons(){ loadingLiveData.setValue((true) backend.loadPersons({ persons : List<Person> -> loadingLiveData.setValue( false ) personsLiveData.setValue( persons ) }, { error: Throwable -> loadingLiveData.setValue( false ) errorLiveData.setValue( error ) }) } }
27. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 What is a Model?
28. data class PersonsModel ( val loading : boolean, val persons : List<Person>?, val error : Throwable? )
29. class PersonsPresenter : Presenter<PersonsView> { fun loadPersons(){ view?.render(PersonsModel ( true, null, null) ) backend.loadPersons({ persons : List<Person> -> view?.render(PersonsModel ( false, persons, null) ) }, { error: Throwable -> view?.render(PersonsModel ( false, null, error) ) }) } }
30. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 Model == State
31. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 How do we change State?
32. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 User
33. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 User
34. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 User Business Logic intent
35. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 User Business Logic intent state
36. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 User Business Logic intent state render(state)
37. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 Model-View-Intent
40. interface SearchView { fun searchIntent() : Observable<String> fun render(viewState : SearchViewState) }
41. data class SearchViewState ( val error : Throwable? val loading: boolean val result : List<Product>? )
42. class SearchFragment : Fragment , SearchView { ... override fun searchIntent() : Observable<String> { return RxSearchView.queryTextChanges(searchView) // Thanks Jake Wharton } }
43. class SearchFragment : Fragment , SearchView { ... override fun render( viewState : SearchViewState) { if (viewState.loading) renderLoading() else if (viewState.result != null) renderResult(viewState.result) else if (viewState.error != null) renderError() else throw IllegalStateException("Unknown ViewState") } }
44. class SearchPresenter : MviBasePresenter<SearchView> { val SearchInteractor searchInteractor; override fun bindIntents() { val searchState : Observable<SearchViewState> = intent(SearchView::searchIntent) .filter { term -> term.size >= 3 } .switchMap(searchInteractor::search) subscribeViewState(searchState, SearchView::render) } }
45. class SearchInteractor { val searchEngine : SearchEngine // Makes http calls fun search(searchString : String) : Observable<SearchViewState>{ return searchEngine.searchFor(searchString) // Observable<List<Product>> .map(products -> SearchViewState(false, products, null)) .startWith(SearchViewState(true, null, null)) .onErrorReturn(error -> SearchViewState(false, null, error)); } }
46. class SearchInteractor { val searchEngine : SearchEngine // Makes http calls fun search(searchString : String) : Observable<SearchViewState>{ return searchEngine.searchFor(searchString) // Observable<List<Product>> .map(products -> new SearchViewState(false, products, null)) .startWith(new SearchViewState(true, null, null)) .onErrorReturn(error -> new SearchViewState(false, null, error)); } }
47. class SearchInteractor { val searchEngine : SearchEngine // Makes http calls fun search(searchString : String) : Observable<SearchViewState>{ return searchEngine.searchFor(searchString) // Observable<List<Product>> .map(products -> new SearchViewState(false, products, null)) .startWith(new SearchViewState(true, null, null)) .onErrorReturn(error -> new SearchViewState(false, null, error)); } }
48. class SearchInteractor { val searchEngine : SearchEngine // Makes http calls fun search(searchString : String) : Observable<SearchViewState>{ return searchEngine.searchFor(searchString) // Observable<List<Product>> .map(products -> new SearchViewState(false, products, null)) .startWith(new SearchViewState(true, null, null)) .onErrorReturn(error -> new SearchViewState(false, null, error)); } }
49. class SearchInteractor { val searchEngine : SearchEngine // Makes http calls fun search(searchString : String) : Observable<SearchViewState>{ return searchEngine.searchFor(searchString) // Observable<List<Product>> .map(products -> new SearchViewState(false, products, null)) .startWith(new SearchViewState(true, null, null)) .onErrorReturn(error -> new SearchViewState(false, null, error)); } }
50. Search … searchIntent view.render( model )
51. C searchIntent filter() C view.render( model )
52. Ca searchIntent filter() C Ca view.render( model )
53. Cam searchIntent Cam filter() C Ca view.render( model )
54. Cam searchIntent filter() flatMap() view.render( model ) Cam C Ca Cam
55. Cam searchIntent filter() flatMap() startWith( new Loading() ) Cam C Ca Cam
56. Cam searchIntent filter() flatMap() startWith( new Loading() ) L view.render( SearchViewState.Loading) Cam C Ca Cam
57. Cam searchIntent filter() flatMap() startWith( new Loading() ) L view.render( SearchViewState.Loading) Cam C Ca Cam
58. Cam searchIntent filter() flatMap() startWith( new Loading() ) L view.render( SearchViewState.Loading) Cam C Ca Cam
59. Cam searchIntent filter() flatMap() startWith( new Loading() ) L view.render( SearchViewState.Loading) Cam C Ca Cam
60. Cam searchIntent filter() flatMap() startWith( new Loading() ) L view.render( SearchViewState.Loading) Cam C Ca Cam
61. Cam searchIntent filter() flatMap() startWith( new Loading() ) L Cam C Ca Cam Cam
62. Cam searchIntent filter() flatMap() startWith( new Loading() ) L Cam C Ca Cam Cam
63. Cam searchIntent filter() flatMap() startWith( new Loading() ) L Cam C Ca Cam Cam
64. Cam searchIntent filter() flatMap() startWith( new Loading() ) L Cam C Ca Cam Cam
65. Cam searchIntent filter() flatMap() startWith( new Loading() ) L map( new SR() ) Cam C Ca Cam Cam
66. Cam searchIntent filter() flatMap() startWith( new Loading() ) L map( new SR() ) Cam C Ca Cam Cam
67. Cam searchIntent filter() flatMap() startWith( new Loading() ) L map( new SR() ) SR view.render( SearchViewState.SearchResult ) Cam C Ca Cam Cam
68. Cam searchIntent filter() flatMap() startWith( new Loading() ) L map( new SR() ) SR view.render( SearchViewState.SearchResult ) Cam C Ca Cam Cam
69. Cam searchIntent filter() flatMap() startWith( new Loading() ) L map( new SR() ) SR view.render( SearchViewState.SearchResult ) Cam C Ca Cam Cam
74. interface HomeView { fun loadFirstPageIntent() : Observable<Unit> fun loadNextPageIntent() : Observable<Unit> fun pullToRefreshIntent() : Observable<Unit> fun loadAllProductsFromCategoryIntent() : Observable<String> fun render(viewState : HomeViewState) }
75. class HomePresenter : MviBasePresenter<HomeView> { val HomeFeedLoader feedLoader; override fun bindIntents() { val firstPage : Observable<FeedLoaderState> = ... val pullToRefresh : Observable<FeedLoaderState> = ... val nextPage : Observable<FeedLoaderState> = ... val loadMoreFromCategory : Observable<FeedLoaderState> = ... val allIntents : Observable<FeedLoaderState> = Observable.merge(firstPage, pullToRefresh, nextPage, loadMoreFromCategory) stateObservable : Observable<HomeViewState> = allIntents.scan(this::reduceState) subscribeViewState(stateObservable, HomeView::render) }
76. class HomePresenter : MviBasePresenter<HomeView> { val HomeFeedLoader feedLoader; override fun bindIntents() { val firstPage : Observable<FeedLoaderState> = ... val pullToRefresh : Observable<FeedLoaderState> = ... val nextPage : Observable<FeedLoaderState> = ... val loadMoreFromCategory : Observable<FeedLoaderState> = ... val allIntents : Observable<FeedLoaderState> = Observable.merge(firstPage, pullToRefresh, nextPage, loadMoreFromCategory) stateObservable : Observable<HomeViewState> = allIntents.scan(this::reduceState) subscribeViewState(stateObservable, HomeView::render) }
77. class HomePresenter : MviBasePresenter<HomeView> { val HomeFeedLoader feedLoader; override fun bindIntents() { val firstPage : Observable<FeedLoaderState> = ... val pullToRefresh : Observable<FeedLoaderState> = ... val nextPage : Observable<FeedLoaderState> = ... val loadMoreFromCategory : Observable<FeedLoaderState> = ... val allIntents : Observable<FeedLoaderState> = Observable.merge(firstPage, pullToRefresh, nextPage, loadMoreFromCategory) stateObservable : Observable<HomeViewState> = allIntents.scan(this::reduceState) subscribeViewState(stateObservable, HomeView::render) }
78. class HomePresenter : MviBasePresenter<HomeView> { val HomeFeedLoader feedLoader; override fun bindIntents() { val firstPage : Observable<FeedLoaderState> = ... val pullToRefresh : Observable<FeedLoaderState> = ... val nextPage : Observable<FeedLoaderState> = ... val loadMoreFromCategory : Observable<FeedLoaderState> = ... val allIntents : Observable<FeedLoaderState> = Observable.merge(firstPage, pullToRefresh, nextPage, loadMoreFromCategory) stateObservable : Observable<HomeViewState> = allIntents.scan(this::reduceState) subscribeViewState(stateObservable, HomeView::render) }
79. fun reduceState ( previous : HomeViewState, feedLoaderState : FeedLoaderState ) : HomeViewState { val newState : HomeViewState = … // compute the new State // by taking previous state and foo into account return newState; }
80. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 State Driven by Business Logic
81. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 Microservices
82. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 state
83. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 state state
84. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017
85. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 Independent UI Components
86. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017
87. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017
88. interface SelectedCountToolbar { fun deleteSelectedIntent() : Observable<Unit> fun render(viewState : Int) }
89. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 Reproducible States
90. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017
91. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017
92. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 Testing
93. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 assertEquals (expectedState, actualState)
94. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 More Integration Tests Less Unit tests
95. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 More Integration Tests Less Unit Tests
96. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 Why Unit Tests - Test code in isolation - Reliable (not flaky) - Run fast - Testing UI as part of an Integration Test is senseless, since View is dump
97. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 2 Unit Tests, 0 Integration Test
98. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 2 Unit Tests, 0 Integration Test
99. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 What if we architect and write Test Code the way we write production code?
100. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 Let’s write reactive and reusable Integration Tests
101. class SearchFragment : Fragment , SearchView { ... override fun searchIntent() : Observable<String> { return RxSearchView.queryTextChanges(searchView) } }
102. class SearchFragment : Fragment , SearchView { ... override fun render( viewState : SearchViewState) { if (viewState.loading) renderLoading() else if (viewState.result != null) renderResult(viewState.result) else if (viewState.error != null) renderError() else throw IllegalStateException("Unknown ViewState") } }
103. class SearchFragment : Fragment , SearchView { @Inject var viewBinding : SearchViewBinding override fun searchIntent() : Observable<String> { return viewBinding.searchIntent() } override fun render( viewState : SearchViewState) { viewBinding.render(viewState) } }
104. class SearchViewBinding : SearchView { val rootView : ViewGroup override fun searchIntent() : Observable<String> { return RxSearchView.queryTextChanges(searchView) } override fun render( viewState : SearchViewState) { if (viewState.loading) … } }
105. class TestSearchViewBinding : SearchViewBinding { override fun render( viewState : SearchViewState ) { super.render(viewState) } }
106. class TestSearchViewBinding : SearchViewBinding { var statesList : List<SearchViewState> val renderedStates : BehaviorSubject<List<SearchViewState>> override fun render( viewState : SearchViewState ) { super.render(viewState) statesList = statesList.copyAndAdd(viewState) renderedStates.onNext(statesList) } }
107. class TestSearchViewBinding : SearchViewBinding { var statesList : List<SearchViewState> val renderedStates : BehaviorSubject<List<SearchViewState>> override fun render( viewState : SearchViewState ) { super.render(viewState) statesList = statesList.copyAndAdd(viewState) renderedStates.onNext(statesList) Screenshot.snap(rootView).record() } } http://facebook.github.io/screenshot-tests-for-android
108. class SearchFragmentTest { @Rule val rule = ActivityTestRule()
 val viewBinding : TestSearchViewBinding @Test fun onTyping3CharsShowLoadingThenResults() { onView(withId(…).perform(typeText(“Camera“) val states = viewBinding.renderedStates.blockingFirst() val loading = SearchViewState(true, null, null) val results = SearchViewState(false, someProducts, null) val expectedStates = listOf(loading, results) assertEquals(expectedStates, states) } }
109. class SearchFragmentTest { @Rule val rule = ActivityTestRule()
 val viewBinding : TestSearchViewBinding @Test fun onTyping3CharsShowLoadingThenResults() { onView(withId(…).perform(typeText(“Camera“) val states = viewBinding.renderedStates.blockingFirst() val loading = SearchViewState(true, null, null) val results = SearchViewState(false, someProducts, null) val expectedStates = listOf(loading, results) assertEquals(expectedStates, states) } }
110. class SearchFragmentTest { @Rule val rule = ActivityTestRule()
 val viewBinding : TestSearchViewBinding @Test fun onTyping3CharsShowLoadingThenResults() { onView(withId(…).perform(typeText(“Camera“) val states = viewBinding.renderedStates.blockingFirst() val loading = SearchViewState(true, null, null) val results = SearchViewState(false, someProducts, null) val expectedStates = listOf(loading, results) assertEquals(expectedStates, states) } }
111. class SearchFragmentTest { @Rule val rule = ActivityTestRule()
 val viewBinding : TestSearchViewBinding @Test fun onTyping3CharsShowLoadingThenResults() { onView(withId(…).perform(typeText(“Camera“) val states = viewBinding.renderedStates.blockingFirst() val loading = SearchViewState(true, null, null) val results = SearchViewState(false, someProducts, null) val expectedStates = listOf(loading, results) assertEquals(expectedStates, states) } }
112. class SearchFragmentTest { @Rule val rule = ActivityTestRule()
 val viewBinding : TestSearchViewBinding @Test fun onTyping3CharsShowLoadingThenResults() { onView(withId(…).perform(typeText(“Camera“) val states = viewBinding.renderedStates.blockingFirst() val loading = SearchViewState(true, null, null) val results = SearchViewState(false, someProducts, null) val expectedStates = listOf(loading, results) assertEquals(expectedStates, states) } } INPUT OUTPUT ASSERT.
113. class Inputs (val viewBinding : TestSearchViewBinding) { fun writeIntoSearchBox( term : String) { onView(withId(…).perform(typeText(term) } }
114. class Output (val viewBinding : TestSearchViewBinding) { fun renderedStates() : List<SearchViewState> = viewBinding.renderedStates.blockingFirst() }
115. class Assertions (val inputs : Inputs, val output : Output) { fun loadThenShowResults() = Completable.fromCallable { inputs.writeIntoSearchBox(“Camera“) val states = output.renderedStates() val loading = SearchViewState(true, null, null) val results = SearchViewState(false, someProducts, null) val expectedStates = listOf(loading, results) assertEquals(expectedStates, states) } }
116. class SearchFragmentTest { @Rule val rule = ActivityTestRule()
 val viewBinding : TestSearchViewBinding @Test fun onTyping3CharsShowLoadingThenResults() { val assertions = Assertions ( Inputs(viewBinding) , Output(viewBinding) ) assertions.loadThenShowResults().awaitBlocking() } }
117. class FooAndBarTest { @Rule val rule = ActivityTestRule()
 val viewBinding : TestSearchViewBinding @Test fun fooAndBar() { val fooAssertions = FooAssertions (…) val barAssertions = BarAssertions (…) fooAssertions.something() .concatWith(barAssertions) .blockingAwait() } }
118. class SearchFragmentTest { @Rule val rule = ActivityTestRule()
 val viewBinding : TestSearchViewBinding @Test fun onTyping3CharsShowLoadingThenResults() { val assertions = Assertions ( Inputs(viewBinding) , Output(viewBinding) ) assertions.loadThenShowResults().awaitBlocking() } }
119. class JvmSearchViewTest { @Test fun onTyping3CharsShowLoadingThenResults() { val assertions = Assertions ( JvmInputs(realPresenter) , JvmOutput(realPresenter) ) assertions.loadThenShowResults().awaitBlocking() } }
120. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 Why Unit Tests - Test code in isolation - Reliable (not flaky) - Run fast - Testing UI as part of an Integration Test is senseless, since View is dump
121. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 Model-View-Intent - takes state management serious —> Solves & avoids a lot of problems - Unidirectional dataflow - State driven by business logic - Composable - Easy to test
122. MOBICONF.ORG | 5-6 OCTOBER 2017 #mobiconf2017 Hannes Dorfmann @sockeqwe www.hannesdorfmann.com hannes@tickaroo.com
123. & Q&A questions answers 112
124. THANK YOU! 113