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Mohit Sarveiya Using Jetpack Compose with Square's Molecule Library @heyitsmohit

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Using Jetpack Compose with Square's Molecule Library ● How to setup and use Molecule ● Testing with Molecule ● Molecule Internals ● Example App

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Molecule Problems, Purpose

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Problem

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Problem Flow 1

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Problem Flow 1 Flow 2

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Problem @Composable 
 fun Profile(flow1, flow2) { val state1 by flow1.collectAsState(null) val state2 by flow2.collectAsState(0L) ... }

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Problem @Composable 
 fun Profile(viewModel: ProfilesViewModel) { val state1 by flow1.collectAsState(null) val state2 by flow2.collectAsState(0L) ... } 
 Mixes business logic with view

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Approach Presenter 
 (Composable)

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Approach Events Presenter 
 (Composable)

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Approach Events Presenter 
 (Composable) Molecule

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Approach Events Presenter 
 (Composable) Molecule

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Approach Events Presenter 
 (Composable) Molecule State Flow

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Molecule Purpose 
 Build a StateFlow using Jetpack Compose

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Compose vs Compose UI

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Compose ● General purpose tool for managing tree of nodes.

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Compose ● General purpose tool for managing tree of nodes.

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Compose ● General purpose tool for managing tree of nodes. Node can be anything

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Compose UI ● UI Toolkit

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Compose UI ● UI Toolkit Views, ViewGroup, etc…

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Resources ● A Jetpack Compose by any other name - Jake Wharton ● Compose From First Principles - Leland Richardson

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Molecule ● Kotlin Compiler Plugin ● Continually recomposes based on clock that controls 
 
 when recomposition occurs

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How to use Molecule Setup & Launch molecules

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Problem Flow 1 Flow 2

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Setup View

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Setup View Molecule

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Setup View Molecule Presenter 
 (Composable) State

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Setup View Molecule Presenter 
 (Composable) Events

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Presenter @Composable 
 fun profilePresenter( ... ) { }

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Model sealed class ProfilesModel { object Loading: ProfilesModel() data class Data( ... ): ProfilesModel() }

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Presenter @Composable 
 fun profilePresenter( ... ): ProfileModel { }

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Problem Flow 1 Flow 2

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Presenter @Composable 
 fun profilePresenter(postsFlow, likesFlow): ProfileModel { 
 
 val posts by postsFlow.collectAsState(null) val likes by likesFlow.collectAsState(0L) return if (posts == null) { ProfileModel.Loading } else { ProfileModel.Success(posts, likes) } }

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Presenter @Composable 
 fun profilePresenter(postsFlow, likesFlow): ProfileModel { 
 
 val posts by postsFlow.collectAsState(null) val likes by likesFlow.collectAsState(0L) return if (posts == null) { ProfileModel.Loading } else { ProfileModel.Success(posts, likes) } }

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Presenter @Composable 
 fun profilePresenter(postsFlow, likesFlow): ProfileModel { 
 
 val posts by postsFlow.collectAsState(null) val likes by likesFlow.collectAsState(0L) return if (posts == null) { ProfileModel.Loading } else { ProfileModel.Success(posts, likes) } }

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Presenter @Composable 
 fun profilePresenter(postsFlow, likesFlow): ProfileModel { 
 
 val posts by postsFlow.collectAsState(null) val likes by likesFlow.collectAsState(0L) return if (posts == null) { ProfileModel.Loading } else { ProfileModel.Success(posts, likes) } }

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Presenter @Composable 
 fun profilePresenter(postsFlow, likesFlow): ProfileModel { 
 
 val posts by postsFlow.collectAsState(null) val likes by likesFlow.collectAsState(0L) return if (posts == null) { ProfileModel.Loading } else { ProfileModel.Success(posts, likes) } }

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Presenter @Composable 
 fun profilePresenter(postsFlow, likesFlow): ProfileModel { 
 
 val posts by postsFlow.collectAsState(null) val likes by likesFlow.collectAsState(0L) return if (posts == null) { ProfileModel.Loading } else { ProfileModel.Success(posts, likes) } }

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Setup Molecule Presenter 
 (Composable)

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Setup Molecule Presenter 
 (Composable) StateFlow

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Launching Molecule ● Define a coroutine scope

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Launching Molecule val scope = CoroutineScope(Dispatchers.Main) val models: StateFlow = scope.launchMolecule { userPresenter(postsFlow, likesFlow) }

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Launching Molecule ● Define a coroutine scope ● Specify frame clock

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Monotomic Frame Clock ● Controls when recomposition occurs ● AndroidUiDispatcher ● BroadcastFrameClock

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Launching Molecule val scope = CoroutineScope( Dispatchers.Main + AndroidUiDispatcher.Main )

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Launching Molecule ● Define a coroutine scope ● Specify frame clock ● Use launchMolecule method to return state from presenter

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Launching Molecule val models: StateFlow = scope.launchMolecule { profilePresenter(postsFlow, likesFlow) }

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Setup View Molecule

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View @Composable 
 fun Profile(models: StateFlow) { 
 
 val model by models.collectAsState() when(model) { UsersModel.Loading -> ... UsersModel.Success -> ...
 } }

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View @Composable 
 fun Profile(models: StateFlow) { 
 
 val model by models.collectAsState() when(model) { UsersModel.Loading -> ... UsersModel.Success -> ...
 } }

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View @Composable 
 fun Profile(models: StateFlow) { 
 
 val model by models.collectAsState() when(model) { ProfileModel.Loading -> ... ProfileModel.Success -> ...
 } }

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Setup View Presenter 
 (Composable)

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Setup View View Model

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Resources ● Try out Molecule in Tivi App by Chris Banes

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View Model class ProfileViewModel: ViewModel() { 
 private val moleculeScope = CoroutineScope( viewModelScope.coroutineContext + AndroidUiDispatcher.Main ) }

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View Model class ProfileViewModel: ViewModel() { 
 private val moleculeScope = CoroutineScope( viewModelScope.coroutineContext + AndroidUiDispatcher.Main ) }

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View Model class ProfileViewModel: ViewModel() { 
 val stateFlow: StateFlow }

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View Model class ProfileViewModel: ViewModel() { 
 val stateFlow = moleculeScope.launchMolecule { } }

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View Model class ProfileViewModel: ViewModel() { 
 
 val stateFlow = moleculeScope.launchMolecule { val posts by postsFlow.collectAsState(null) val likes by likesFlow.collectAsState(0L) return if (posts == null) { ProfileModel.Loading } else { ProfileModel.Success(posts, likes) }

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View Model class ProfileViewModel: ViewModel() { 
 
 val stateFlow = moleculeScope.launchMolecule { val posts by postsFlow.collectAsState(null) val likes by likesFlow.collectAsState(0L) return if (posts == null) { ProfileModel.Loading } else { ProfileModel.Success(posts, likes) }

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Molecule ● How to setup presenter ● How to launch molecules 


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Testing

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Testing val models: StateFlow = scope.launchMolecule { profilePresenter(postsFlow, likesFlow) }

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Test Cases Presenter Model

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Testing ● Uses Turbine ● Turbine is a library for testing flows

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Testing testImplementation "app.cash.molecule:molecule-testing"

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Presenter @Test fun `should get profiles`() { }

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Presenter @Test fun `should get profiles`() { val posts = MutableSharedFlow() val likes = MutableSharedFlow() }

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Presenter @Test fun `should get profiles`() { testMolecule({ }) }

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Presenter @Test fun `should get profiles`() { testMolecule({ profilePresenter(posts, likes) }) }

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Presenter @Test fun `should get profiles`() { testMolecule({ profilePresenter(posts, likes) }) { assertEquals( ProfileModel.Loading, awaitItem() ) } }

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Presenter @Test fun `should get profiles`() { testMolecule({ profilePresenter(posts, likes) }) { posts.emit(data) } }

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Presenter @Test fun `should get profiles`() { testMolecule({ profilePresenter(posts, likes) }) { posts.emit(data) 
 assertEquals( ProfileModel.Success(data), awaitItem() )

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Testing ● Setup tests ● How to use Turbine 


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Molecule Internals

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Internals ● Setup Recomposer ● Schedule recomposition ● Run composition on the passed in body

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Internals fun CoroutineScope.launchMolecule( emitter: (value: T) -> Unit, body: @Composable () -> T, )

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Internals fun CoroutineScope.launchMolecule( emitter: (value: T) -> Unit, body: @Composable () -> T, )

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Launching Molecule val models: StateFlow = scope.launchMolecule { profilePresenter(events) }

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Internals var flow: MutableStateFlow? = null

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Internals var flow: MutableStateFlow? = null launchMolecule( emitter = { value -> outputFlow.value = value }, ... )

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Internals fun CoroutineScope.launchMolecule( emitter: (value: T) -> Unit, body: @Composable () -> T, )

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Internals ● Setup Recomposer

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Internals launchMolecule() { val recomposer = Recomposer(coroutineContext) } Scheduler for performing recomposition

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Internals launchMolecule() { val recomposer = Recomposer(coroutineContext) val composition = Composition(recomposer) } Used to apply composition

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Internals ● Setup Recomposer ● Schedule recomposition

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Internals launchMolecule() { launch { recomposer.runRecomposeAndApplyChanges() } } 
 Suspends 
 
 - Await the invalidation of any associated composers.

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Internals launchMolecule() { Snapshot.registerGlobalWriteObserver { Snapshot.sendApplyNotifications() } } Register an observer 
 Called when a state object is modified

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Internals ● Setup Recomposer ● Schedule recomposition ● Run composition on the passed in body

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Internals launchMolecule() { composition.setContent { emitter(body()) } } Update composition

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Launching Molecule val models: StateFlow = scope.launchMolecule { profilePresenter(events) }

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Example App

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Android App Example ● How to use it in multiple presenters ● Launching Molecules

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No content

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Screens ● Displays scores ● Player info ● Weather info

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Multiplatform App Shared Android iOS GraphQL

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Architecture View Presenter Events

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Architecture View Presenter Model

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Presenter @Composable 
 fun profilePresenter(postsFlow, likesFlow): ProfileModel { 
 
 val posts by postsFlow.collectAsState(null) val likes by likesFlow.collectAsState(0L) return if (posts == null) { ProfileModel.Loading } else { ProfileModel.Success(posts, likes) } }

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Questions ● How do you setup the Presenter with Dagger?

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Presenter class ScoresPresenter @Inject constructor() { }

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Presenter @Composable 
 fun profilePresenter(postsFlow, likesFlow): ProfileModel { 
 
 val posts by postsFlow.collectAsState(null) val likes by likesFlow.collectAsState(0L) return if (posts == null) { ProfileModel.Loading } else { ProfileModel.Success(posts, likes) } }

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Questions ● How do you setup the composable?

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Presenter class ScoresPresenter @Inject constructor() { @Composable fun present(events): ScoresModel { } }

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Screens ● Displays scores ● Player info ● Weather info

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Presenter class PlayersPresenter @Inject constructor() { @Composable fun present(events): PlayersModel { } }

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Questions ● How do you create a pattern for setting up multiple 
 
 presenter?

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Presenter interface MoleculePresenter { @Composable fun present(events: Flow): Model }

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Presenter class ScoresPresenter: MoleculePresenter { @Composable override fun present(events): ScoresModel { } }

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Questions ● How do you launch molecules for the presenter?

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Navigation Players Navigator Scores Weather

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Navigator @Composable fun AppNavigator( scoresModels: StateFlow, playersModels: StateFlow, weatherModels: StateFlow )

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Navigator class MainActivity : ComponentActivity() { override fun onCreate() { setContent { } } }

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Navigator class MainActivity : ComponentActivity() { override fun onCreate() { setContent { AppNavigator( ... ) } } }

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class MainActivity : ComponentActivity() { val scoresModels = scope.launchMolecule { scoresPresenter.present(events = scoresFlow) } } Launching Molecules

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class MainActivity : ComponentActivity() { val scoresModels = scope.launchMolecule { scoresPresenter.present(events = scoresFlow) } val playerModels = scope.launchMolecule { playersPresenter.present(events = playersFlow) } } Launching Molecules

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Navigator class MainActivity : ComponentActivity() { override fun onCreate() { setContent { AppNavigator( playersModels, scoresModels ) } } }

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Approach Players Main Activity Scores Weather

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Approach Players Main Activity Scores Weather Screen ……

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class MainActivity : ComponentActivity() { val scoresModels = scope.launchMolecule { scoresPresenter.present(events = scoresFlow) } } Launching Molecules

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Questions ● How do you setup launching molecules for many 
 presenters?

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class MainActivity : ComponentActivity() { @Inject lateinit var scoresPresenter: ScoresPresenter @Inject lateinit var weatherPresenter: WeatherPresenter } Dependency Injection

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Questions ● How do you setup DI with single activity multiple 
 
 composable?

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Feedback

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Feedback

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Feedback val scoresFlow = remember { simulator.simulate(speed = 1000) } val scoresModel = scoresPresenter.present(events = scoresFlow) ScoresScreen( tournamentInfoModel, scoresModel )

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Feedback val scoresFlow = remember { simulator.simulate(speed = 1000) } val scoresModel = scoresPresenter.present(events = scoresFlow) ScoresScreen( tournamentInfoModel, scoresModel )

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Feedback val scoresFlow = remember { simulator.simulate(speed = 1000) } val scoresModel = scoresPresenter.present(events = scoresFlow) ScoresScreen( scoresModel )

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Using Jetpack Compose with Square's Molecule Library ● How to setup and use Molecule ● Testing with Molecule ● Molecule Internals ● Example App

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Resources ● Using Jetpack Compose with Molecule Library ● Molecule Library

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Resources

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Thank You! www.codingwithmohit.com @heyitsmohit