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@chris_h_codes
Molecule
Using Compose for presentation logic
Chris Horner
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Compose. Not Compose UI.
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Presentation logic?
MV Whatever
Model
Event
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What does Molecule enable?
@Composable
fun models(events: Flow): Model {
//
Calculate Model here.
}
Why is this interesting?
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2017
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2017
RxJava
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class MyActivity : Activity() {
override fun onCreate(savedInstanceState: Bundle?) {
button.setOnClickListener {
}
}
}
2010
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class MyActivity : Activity() {
override fun onCreate(savedInstanceState: Bundle?) {
button.setOnClickListener {
object : AsyncTask() {
override fun doInBackground(vararg arg: Void?) {
//
Update "state" somehow?
}
}
}
}
}
2010
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<>
Observable
Observable
Observable
Observable
The State of Managing State with RxJava
https://youtu.be/0IKHxjkgop4
Jake Wharton
2017
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2017
Single.just(input)
.flatMap { longRunningOp(it) }
.map { it.asSomethingElse() }
.filter { someCheck(it) }
.subscribe { … }
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2017
Single.just(input)
.flatMap { longRunningOp(it) }
.map { it.asSomethingElse() }
.filter { someCheck(it) }
.subscribe { … }
val result = longRunningOp(input)
val output = result.asSomethingElse()
return if someCheck(output) output else null
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2017
Single.just(input)
.flatMap { longRunningOp(it) }
.map { it.asSomethingElse() }
.filter { someCheck(it) }
.subscribeOn(Schedulers.Io)
.observeOn(Schedulers.Main)
.subscribe { … }
val result = longRunningOp(input)
val output = result.asSomethingElse()
return if someCheck(output) output else null
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Single Maybe Completable
suspend
2017
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2019
fun map(mapper: (T)
->
R): Flowable
fun flatMapSingle(mapper: (T)
->
SingleSource): Flowable
Mapper
Asynchronous Data Streams with Kotlin Flow
https://youtu.be/tYcqn48SMT8
Roman Elizarov
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2019
Sync
Async
fun map(mapper: (T)
->
R): Flowable
fun flatMapSingle(mapper: (T)
->
SingleSource): Flowable
Mapper
Asynchronous Data Streams with Kotlin Flow
https://youtu.be/tYcqn48SMT8
Roman Elizarov
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fun map(mapper: (T)
->
R): Flowable
fun flatMapSingle(mapper: (T)
->
SingleSource): Flowable
Mapper
2019
fun filter(predicate: (T)
->
Boolean): Flowable
fun …
🤯
Predicate
Sync
Async
Sync
Async
Asynchronous Data Streams with Kotlin Flow
https://youtu.be/tYcqn48SMT8
Roman Elizarov
Asynchronous Data Streams with Kotlin Flow
https://youtu.be/tYcqn48SMT8
Roman Elizarov
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flow.map {
}
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Operator Avoidance
startWith(observable)
startWith(value)
delaySubscription(time)
onStart { emitAll(flow) }
onStart { emit(value) }
onStart { delay(time) }
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Operator Avoidance
RxJava API surface
Flow API surface
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Operator Avoidance
RxJava API surface
Flow API surface
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Operator Power
val queries: Flowable
sealed interface Model {
object Loading : Model
data class Loaded(
val results: List
): Model
}
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Operator Power
Mel
val queries: Flowable
sealed interface Model {
object Loading : Model
data class Loaded(
val results: List
): Model
}
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Operator Power
Mel
val queries: Flowable
sealed interface Model {
object Loading : Model
data class Loaded(
val results: List
): Model
}
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Operator Power
queries.switchMap { query
-
>
search(query)
.delaySubscription(300, TimeUnit.MILLISECONDS)
.toObservable()
.startWith { Model.Loading }
}
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Operator Power
queries.switchMap { query
-
>
search(query)
.delaySubscription(300, TimeUnit.MILLISECONDS)
.toObservable()
.startWith { Model.Loading }
}
queries.transformLatest { query
->
emit(Model.Loading)
delay(300)
emit(search(query))
}
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Operator Power
queries.switchMap { query
-
>
search(query)
.delaySubscription(300, TimeUnit.MILLISECONDS)
.toObservable()
.startWith { Model.Loading }
}
queries.transformLatest { query
->
emit(Model.Loading)
delay(300)
emit(search(query))
}
1
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Operator Power
queries.switchMap { query
-
>
search(query)
.delaySubscription(300, TimeUnit.MILLISECONDS)
.toObservable()
.startWith { Model.Loading }
}
queries.transformLatest { query
->
emit(Model.Loading)
delay(300)
emit(search(query))
}
2
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Operator Power
queries.switchMap { query
-
>
search(query)
.delaySubscription(300, TimeUnit.MILLISECONDS)
.toObservable()
.startWith { Model.Loading }
}
queries.transformLatest { query
->
emit(Model.Loading)
delay(300)
emit(search(query))
}
3
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Operator Power
queries.switchMap { query
-
>
search(query)
.delaySubscription(300, TimeUnit.MILLISECONDS)
.toObservable()
.startWith { Model.Loading }
}
queries.transformLatest { query
->
emit(Model.Loading)
delay(300)
emit(search(query))
}
1
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Operator Power
queries.switchMap { query
-
>
search(query)
.delaySubscription(300, TimeUnit.MILLISECONDS)
.toObservable()
.startWith { Model.Loading }
}
queries.transformLatest { query
->
emit(Model.Loading)
delay(300)
emit(search(query))
}
2
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Operator Power
queries.switchMap { query
-
>
search(query)
.delaySubscription(300, TimeUnit.MILLISECONDS)
.toObservable()
.startWith { Model.Loading }
}
queries.transformLatest { query
->
emit(Model.Loading)
delay(300)
emit(search(query))
}
3
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So suspend + Flow wins. End of story?
• suspend is great because we can write imperative code
• Flow has advantages over Rx because it’s powered by coroutines
• It still has many operators to learn
• It’s still a slightly different way of writing code
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No content
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queries.transformLatest { query
->
emit(State.Loading)
delay(300)
emit(search(query))
}
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queries
.map {
...
}
.transformLatest { query
->
emit(State.Loading)
delay(300)
emit(search(query))
}
.flowOn(
.. .
)
.onEmpty {
...
}
.catch {
.. .
}
.scan(emptyList()) { list, items
->
list + items
.map {
...
}
.zip()
}
.flatMapMerge(concurrency = 4) {
..
.
}
.distinctUntilChanged()
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What are we doing?
We’re composing a model in response to
events and values changing over time.
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What if we actually used Compose to
build that model?
Molecule asks the question:
What are we doing?
We’re composing a model in response to
events and values changing over time.
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Column
Text Row
Column Image
Text Text
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Column
Text Row
Column Image
Text Text
@Composable
fun UserInterface(model: Model) {
}
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Column
Text Row
Box Image
Image Icon
@Composable
fun UserInterface(model: Model) {
}
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Column
Text Row
Image
@Composable
fun UserInterface(model: Model) {
var someState: Int by remember {
mutableStateOf(1)
}
}
Box
Image Icon
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@Composable
fun UserInterface(model: Model) {
val someState: MutableState = remember {
mutableStateOf(1)
}
}
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@Composable
fun UserInterface(model: Model) {
val state: State
}
Reactive!
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@Composable
fun UserInterface(model: Model) {
var someState: Int by remember {
mutableStateOf(1)
}
}
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@Composable
fun UserInterface() {
var someState: Int by remember {
mutableStateOf(1)
}
LaunchedEffect(Unit) {
while (true) {
delay(1_000)
someState
++
}
}
}
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@Composable
fun UserInterface() {
var someState: Int by remember {
mutableStateOf(1)
}
LaunchedEffect(Unit) {
while (true) {
delay(1_000)
someState
++
}
}
Text(someState.toString())
}
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@Composable
fun UserInterface() {
var someState: Int by remember {
mutableStateOf(1)
}
LaunchedEffect(Unit) {
while (true) {
delay(1_000)
someState
++
}
}
Text(someState.toString())
}
Presentation logic
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@Composable
fun UserInterface() {
}
Flow Example
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@Composable
fun UserInterface() {
}
sealed interface Model {
object Loading : Model
data class Loaded(
val results: List
) : Model
}
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@Composable
fun UserInterface(queries: Flow) {
}
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@Composable
fun UserInterface(queries: Flow) {
val models = queries
.onStart { emit("") }
}
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@Composable
fun UserInterface(queries: Flow) {
val models = queries
.onStart { emit("") }
.transformLatest { query
->
emit(Model.Loading)
}
}
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@Composable
fun UserInterface(queries: Flow) {
val models = queries
.onStart { emit("") }
.transformLatest { query
->
emit(Model.Loading)
delay(300)
val results = search(query)
emit(Model.Loaded(results))
}
}
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e
terface(queries: Flow) {
ls = queries
rt { emit("") }
formLatest { query
->
(Model.Loading)
y(300)
results = search(query)
(Model.Loaded(results))
interface Database {
fun observeDataset(): Flow
}
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e
terface(queries: Flow) {
ls = queries
rt { emit("") }
formLatest { query
->
(Model.Loading)
y(300)
results = search(query, dataset)
(Model.Loaded(results))
interface Database {
fun observeDataset(): Flow
}
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@Composable
fun UserInterface(queries: Flow) {
val models = queries
.onStart { emit("") }
.transformLatest { query
->
emit(Model.Loading)
delay(300)
val results = search(query, dataset)
emit(Model.Loaded(results))
}
}
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
val models = queries
.onStart { emit("") }
.transformLatest { query
->
emit(Model.Loading)
delay(300)
val results = search(query, dataset)
emit(Model.Loaded(results))
}
}
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
combineTransform(queries, datasets)
val models = queries
.onStart { emit("") }
.transformLatest { query
->
emit(Model.Loading)
delay(300)
val results = search(query, dataset)
emit(Model.Loaded(results))
}
}
?
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
combineTransformLatest(queries, dataset)
val models = queries
.onStart { emit("") }
.transformLatest { query
->
emit(Model.Loading)
delay(300)
val results = search(query, dataset)
emit(Model.Loaded(results))
}
}
?
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
val models = datasets.flatMapLatest { dataset
->
queries
.onStart { emit("") }
.transformLatest { query
-
>
emit(Model.Loading)
delay(300)
val results = search(query, dataset)
emit(Model.Loaded(results))
}
}
}
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What if we used Compose?
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
val models = datasets.flatMapLatest { dataset
->
queries
.onStart { emit("") }
.transformLatest { query
-
>
emit(Model.Loading)
delay(300)
val results = search(query, dataset)
emit(Model.Loaded(results))
}
}
}
What if we used Compose?
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
val query by queries.collectAsState("")
val models = dataset
s
.flatMapLatest { dataset
->
queries
.onStart { emit("") }
.transformLatest { query
-
>
emit(Model.Loading)
delay(300)
val results = search(query, dataset)
emit(Model.Loaded(results))
}
}
}
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
val query by queries.collectAsState("")
val dataset by datasets.collectAsState(InitialSet)
val models = dataset
s
.flatMapLatest { dataset
->
queries
.onStart { emit("") }
.transformLatest { query
-
>
emit(Model.Loading)
delay(300)
val results = search(query, dataset)
emit(Model.Loaded(results))
}
}
}
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
val query by queries.collectAsState("")
val dataset by datasets.collectAsState(InitialSet)
var model by remember { mutableStateOf(Model.Loaded(emptyList())) }
val models = dataset
s
.flatMapLatest { dataset
->
queries
.onStart { emit("") }
.transformLatest { query
-
>
emit(Model.Loading)
delay(300)
val results = search(query, dataset)
emit(Model.Loaded(results))
}
}
}
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
val query by queries.collectAsState("")
val dataset by datasets.collectAsState(InitialSet)
var model by remember { mutableStateOf(Model.Loaded(emptyList())) }
val models = dataset
s
.flatMapLatest { dataset
->
queries
.onStart { emit("") }
.transformLatest { query
-
>
emit(Model.Loading)
delay(300)
val results = search(query, dataset)
emit(Model.Loaded(results
)
)
}
}
}
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
val query by queries.collectAsState("")
val dataset by datasets.collectAsState(InitialSet)
var model by remember { mutableStateOf(Model.Loaded(emptyList())) }
LaunchedEffect(query, dataset) {
emit(Model.Loading)
delay(300)
val results = search(query, dataset)
emit(Model.Loaded(results
)
)
}
}
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
val query by queries.collectAsState("")
val dataset by datasets.collectAsState(InitialSet)
var model by remember { mutableStateOf(Model.Loaded(emptyList())) }
LaunchedEffect(query, dataset) {
model = Model.Loading
delay(300)
val results = search(query, dataset)
model = Model.Loaded(results)
}
}
Still reactive!
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
}
• flatMap
• scan
• debounce
• zip
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
}
• remember
• LaunchedEffect
• collectAsState
• mutableStateOf
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
}
• remember
• LaunchedEffect
• collectAsState
• mutableStateOf
• if, else, when, for, while
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
val query by queries.collectAsState("")
val dataset by datasets.collectAsState(InitialSet)
var model by remember { mutableStateOf(Model.Loaded(emptyList())) }
LaunchedEffect(query, dataset) {
model = Model.Loading
delay(300)
val results = search(query, dataset)
model = Model.Loaded(results)
}
}
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
val query by queries.collectAsState("")
val dataset by datasets.collectAsState(InitialSet)
var model by remember { mutableStateOf(Model.Loaded(emptyList())) }
LaunchedEffect(query, dataset) {
model =
Model.Loadin
g
delay(300)
val results = search(query, dataset)
model =
Model.Loaded(results)
}
Column {
// .. .
}
}
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@Composable
fun UserInterface(queries: Flow, datasets: Flow) {
val query by queries.collectAsState("")
val dataset by datasets.collectAsState(InitialSet)
var model by remember { mutableStateOf(Model.Loaded(emptyList())) }
LaunchedEffect(query, dataset) {
model = Model.Loading
delay(300)
val results = search(query, dataset)
model = Model.Loaded(results)
}
Column {
// .. .
}
}
Presentation logic
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Why do we need Molecule?
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Why do we need Molecule?
presentation-logic
ui
@Composable
StateFlow
junit
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Why do we need Molecule?
presentation-logic
ui
@Composable
StateFlow
junit
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How do we use it?
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How do we use it?
apply plugin: 'app.cash.molecule'
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How do we use it?
Flow StateFlow
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How do we use it?
Flow StateFlow
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How do we use it?
val scope = CoroutineScope(AndroidUiDispatcher.Main)
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How do we use it?
val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
}
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How do we use it?
val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
}
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val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
}
}
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val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
}
model
}
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val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
}
model
}
1
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val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
}
model
}
2
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val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
}
model
}
3
A
Emissions
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val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
}
model
}
4
A
Emissions
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val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
}
model
}
5
A
Emissions
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6
A B
val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
}
model
}
Emissions
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val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
model = Model(C)
}
model
}
A B
Emissions
?
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val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
model = Model(C)
}
model
}
A B C
Emissions
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val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
model
}
• Some State is invalidated
• A MonotonicFrameClock ticks
For a new emission, two things must happen
Emissions
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val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
model = Model(C)
}
model
}
A B C
Emissions
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A B C
Emissions
val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
model = Model(C)
}
model
}
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A B C
Frame tick
Emissions
val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
model = Model(C)
}
model
}
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A B C
Emissions
val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
model = Model(C)
}
model
}
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A B C
Emissions
C
val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
model = Model(C)
}
model
}
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A B C
Emissions
val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
model = Model(C)
}
model
}
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val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule() {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
model = Model(C)
}
model
}
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val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule(
clock = RecompositionClock.ContextClock
) {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
model = Model(C)
}
model
}
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val scope = CoroutineScope(AndroidUiDispatcher.Main)
val models: StateFlow = scope.launchMolecule(
clock = RecompositionClock.ContextClock
) {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
model = Model(C)
}
model
}
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val scope = CoroutineScope
(
)
val models: StateFlow = scope.launchMolecule(
clock = RecompositionClock.ContextClock
) {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
model = Model(C)
}
model
}
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fun unitTest() = runBlocking {
val scope = this
val models: StateFlow = scope.launchMolecule(
clock = RecompositionClock.ContextClock
) {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
model = Model(C)
}
model
}
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fun unitTest() = runBlocking {
val scope = this
val models: StateFlow = scope.launchMolecule(
clock = RecompositionClock.Immediate
) {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
model = Model(C)
}
model
}
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fun unitTest() = runBlocking {
val scope = this
val models: StateFlow = scope.launchMolecule(
clock = RecompositionClock.Immediate
) {
var model by remember { mutableStateOf(Model(A)) }
LaunchedEffect(Unit) {
model = loadModelB()
model = Model(C)
}
model
}
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ContextClock
Immediate
• Emissions match Android’s built in frame clock
• Need to control emissions using BroadcastFrameClock
• Unit tests requiring time manipulation
Choosing a RecompositionClock
• Frames tick automatically when snapshot state changes
• Unit tests that don’t require time manipulation
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You only get one emission per
frame
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Realistic example
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Realistic example
class Presenter {
@Composable
fun models(events: Flow): Model {
//
Calculate Model here.
}
}
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Realistic example
class Presenter {
@Composable
fun models(events: Flow): Model {
//
Calculate Model here.
}
}
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class SearchPresenter : Presenter {
@Composable
fun models(events: Flow): Model {
//
Calculate Model here.
}
}
Realistic example
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sealed interface Event {
data class EnterText(val text: String) : Event
}
sealed interface Model {
object Loading : Model
data class Loaded(
val results: List = emptyList()
) : Model
}
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class SearchPresenter : Presenter {
@Composable
fun models(events: Flow): Model {
//
Calculate Model here.
}
}
Realistic example
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class SearchPresenter(
val service: Service
) : Presenter {
@Composable
fun models(events: Flow): Model {
//
Calculate Model here.
}
}
Realistic example
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class SearchPresenter(
val service: Service
) : Presenter {
@Composable
fun models(events: Flow): Model {
val modelState = remember { mutableStateOf(Model.Loaded()) }
}
}
Realistic example
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class SearchPresenter(
val service: Service
) : Presenter {
@Composable
fun models(events: Flow): Model {
val modelState: MutableState = remember { mutableStateOf(Mod
}
}
Realistic example
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class SearchPresenter(
val service: Service
) : Presenter {
@Composable
fun models(events: Flow): Model {
val modelState = remember { mutableStateOf(Model.Loaded()) }
}
}
Realistic example
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class SearchPresenter(
val service: Service
) : Presenter {
@Composable
fun models(events: Flow): Model {
val modelState = remember { mutableStateOf(Model.Loaded()) }
return modelState.value
}
}
Realistic example
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class SearchPresenter(
val service: Service
) : Presenter {
@Composable
fun models(events: Flow): Model {
val modelState = remember { mutableStateOf(Model.Loaded()) }
LaunchedEffect(Unit) {
events.collect { event
->
when (event) {
...
}
}
}
return modelState.value
}
}
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class SearchPresenter(
val service: Service
) : Presenter {
@Composable
fun models(events: Flow): Model {
val modelState = remember { mutableStateOf(Model.Loaded()) }
var query by remember { mutableStateOf("") }
LaunchedEffect(Unit) {
events.collect { event
->
when (event) {
EnterText
->
query = event.text
}
}
}
return modelState.value
}
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@Composable
fun models(events: Flow): Model {
val modelState = remember { mutableStateOf(Model.Loaded()) }
var query by remember { mutableStateOf("") }
LaunchedEffect(Unit) {
events.collect { event
->
when (event) {
EnterText
->
query = event.text
}
}
}
LaunchedEffect(query) {
runSearch(query, modelState)
}
return modelState.value
}
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private suspend fun runSearch(
query: String,
state: MutableState,
) {
state.value = Model.Loading
val results = service.search(query)
state.value = Model.Loaded(results)
}
LaunchedEffect(query) {
runSearch(query, modelState)
}
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private suspend fun runSearch(
query: String,
state: MutableState,
) {
state.value = Model.Loading
val results = service.search(query)
state.value = Model.Loaded(results)
}
LaunchedEffect(query) {
runSearch(query, modelState)
}
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private suspend fun runSearch(
query: String,
state: MutableState,
) {
state.value = Model.Loading
val results = service.search(query)
state.value = Model.Loaded(results)
}
LaunchedEffect(query) {
runSearch(query, modelState)
}
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Writing a test
cashapp/turbine
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cashapp/turbine
Writing a test
flowOf("one", "two").test {
assertEquals("one", awaitItem())
assertEquals("two", awaitItem())
awaitComplete()
}
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Writing a test
@Test
fun `entering text runs search`() = runBlocking {
}
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Writing a test
@Test
fun `entering text runs search`() = runBlocking {
val events = MutableSharedFlow(replay = 1)
}
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Writing a test
@Test
fun `entering text runs search`() = runBlocking {
val events = MutableSharedFlow(replay = 1)
launchMolecule(RecompositionClock.Immediate) {
presenter.models(events)
}.test {
}
}
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Writing a test
@Test
fun `entering text runs search`() = runBlocking {
val events = MutableSharedFlow(replay = 1)
launchMolecule(RecompositionClock.Immediate) {
presenter.models(events)
}.test {
assertThat(awaitItem()).isEqualTo(Model.Loading)
}
}
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Writing a test
@Test
fun `entering text runs search`() = runBlocking {
val events = MutableSharedFlow(replay = 1)
launchMolecule(RecompositionClock.Immediate) {
presenter.models(events)
}.test {
assertThat(awaitItem()).isEqualTo(Model.Loading)
events.emit(Event.EnterText("query"))
fakeService.setResults(
..
.
)
}
}
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Writing a test
@Test
fun `entering text runs search`() = runBlocking {
val events = MutableSharedFlow(replay = 1)
launchMolecule(RecompositionClock.Immediate) {
presenter.models(events)
}.test {
assertThat(awaitItem()).isEqualTo(Model.Loading)
events.emit(Event.EnterText("query"))
fakeService.setResults(
..
.
)
assertThat(awaitItem()).isEqualTo(Model.Loaded(
..
.
))
}
}
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Writing a test
@Test
fun `entering text runs search`() = runBlocking {
presenter.test {
assertThat(awaitItem()).isEqualTo(Model.Loading)
sendEvent(Event.EnterText("query"))
fakeService.setResults(
..
.
)
assertThat(awaitItem()).isEqualTo(Model.Loaded(
..
.
))
}
}
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Takeaways
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Takeaways
• Compose manages a tree of nodes - it doesn’t have to be UI
• Managing state involves tying together streams
• Compose can do to streams what suspend did to Single
• State is reactive. Think of it like a stream
• There’s still a learning curve, but it’s less steep compared to Rx/Flow
• Tricks you’ve learnt in Compose UI work in Molecule too
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Interested in more?
Building StateFlows with Jetpack Compose
droidcon.com/2022/09/29/building-stateflows-in-android-with-jetpack-compose
Mohit Sarveiya
Demystifying Molecule
droidcon.com/2022/09/29/demystifying-molecule-running-your-own-compositions-for-fun-and-profit
Bill Phillips & Ash Davies
Opening the Shutter on Snapshots
droidcon.com/2022/09/29/opening-the-shutter-on-snapshots
Zach Klippenstein
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chris_h_codes
github.com/cashapp/molecule
Molecule
Using Compose for presentation logic