Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
Migrating to Kotlin State & Shared Flows
Search
Mohit S
June 03, 2022
Programming
1
780
Migrating to Kotlin State & Shared Flows
Mohit S
June 03, 2022
Tweet
Share
More Decks by Mohit S
See All by Mohit S
Guide to Improving Compose Performance
heyitsmohit
0
220
Building Shared UIs across Platforms with Compose
heyitsmohit
1
620
Building Multiplatform Apps with Compose
heyitsmohit
2
500
Building StateFlows with Jetpack Compose
heyitsmohit
6
1.8k
Building Android Testing Infrastructure
heyitsmohit
1
470
Using Square Workflow for Android & iOS
heyitsmohit
1
420
Building Android Infrastructure Teams at Scale
heyitsmohit
3
310
Strategies for Migrating to Jetpack Compose
heyitsmohit
2
550
Challenges of Building Kotlin Multiplatform Libraries
heyitsmohit
1
430
Other Decks in Programming
See All in Programming
Select API from Kotlin Coroutine
jmatsu
1
160
Create a website using Spatial Web
akkeylab
0
290
人には人それぞれのサービス層がある
shimabox
3
680
GraphRAGの仕組みまるわかり
tosuri13
7
380
Beyond Portability: Live Migration for Evolving WebAssembly Workloads
chikuwait
0
370
実はすごいスピードで進化しているCSS
hayato_yokoyama
0
120
Java on Azure で LangGraph!
kohei3110
0
140
Enterprise Web App. Development (2): Version Control Tool Training Ver. 5.1
knakagawa
1
110
赤裸々に公開。 TSKaigiのオフシーズン
takezoux2
0
130
AWS CDKの推しポイント 〜CloudFormationと比較してみた〜
akihisaikeda
3
280
Rails産でないDBを Railsに引っ越すHACK - Omotesando.rb #110
lnit
1
160
生成AIコーディングとの向き合い方、AIと共創するという考え方 / How to deal with generative AI coding and the concept of co-creating with AI
seike460
PRO
1
290
Featured
See All Featured
Let's Do A Bunch of Simple Stuff to Make Websites Faster
chriscoyier
507
140k
Connecting the Dots Between Site Speed, User Experience & Your Business [WebExpo 2025]
tammyeverts
4
170
The Art of Programming - Codeland 2020
erikaheidi
54
13k
Optimising Largest Contentful Paint
csswizardry
37
3.3k
VelocityConf: Rendering Performance Case Studies
addyosmani
329
24k
We Have a Design System, Now What?
morganepeng
52
7.6k
Embracing the Ebb and Flow
colly
86
4.7k
A designer walks into a library…
pauljervisheath
206
24k
KATA
mclloyd
29
14k
YesSQL, Process and Tooling at Scale
rocio
172
14k
RailsConf & Balkan Ruby 2019: The Past, Present, and Future of Rails at GitHub
eileencodes
137
34k
Fight the Zombie Pattern Library - RWD Summit 2016
marcelosomers
233
17k
Transcript
Mohit Sarveiya Migrating to Kotlin State & Shared Flows @heyitsmohit
Migrating to Kotlin State & Shared Flows • State &
Shared Flow APIs • Migrating from broadcast channels • Flow Sharing Strategies • Manage Backpressure
Cold vs Hot Flows
What is a cold stream? • Flow completes • Triggers
same code for every new subscriber
Cold Flows val flow = flowOf(1, 2, 3) .map
{ it + 1 }
Cold Flows val flow = flowOf(1, 2, 3) .map
{ it + 1 } flow.collect { ... }
Cold Flows val flow = flowOf(1, 2, 3) .map
{ it + 1 } flow.collect { ... }
Cold Flows val flow = flowOf(1, 2, 3) .map
{ it + 1 } flow.collect { ... }
Cold Flows val flow = flowOf(1, 2, 3) .map
{ it + 1 } flow.collect { // 2, 3, 4 }
Cold Flows val flow = flowOf(1, 2, 3) .map
{ it + 1 } flow.collect { ... } flow.collect { ... }
Cold Flows val flow = flowOf(1, 2, 3) .map
{ it + 1 } flow.collect { ... } flow.collect { ... }
Cold Flows val flow = flowOf(1, 2, 3) .map
{ it + 1 } flow.collect { ... } flow.collect { ... }
Cold Flows val flow = flowOf(1, 2, 3) .map
{ it + 1 } flow.collect { ... } flow.collect { // 2, 3, 4 }
What is a hot stream? • Never completes normally •
Exists independently of subscribers.
Hot Streams State Flow Shared Flow
State Flow • Different ways to create state flows •
Emit, collect • Conflation
State Flow View View Model
State Flow View View Model State
State Flow sealed class UiState { object Loading: UiState()
data class Success(…): UiState() data class Error(…): UiState() }
State Flow sealed class UiState { object Loading: UiState()
data class Success(…): UiState() data class Error(…): UiState() }
State Flow sealed class UiState { object Loading: UiState()
data class Success(…): UiState() data class Error(…): UiState() }
State Flow val stateFlow = MutableStateFlow()
val stateFlow = MutableStateFlow( UiState.Loading ) State Flow
State Flow val stateFlow = MutableStateFlow( . .. ) stateFlow.emit(
UIState.Success( ... ) )
State Flow val stateFlow = MutableStateFlow( . .. ) stateFlow.value
= UIState.Success( ... )
State Flow val stateFlow = MutableStateFlow( . .. ) stateFlow.update
{ UIState.Success( .. . ) }
State Flow val stateFlow = MutableStateFlow( . .. ) stateFlow.collect
{ .. . } stateFlow.collect { .. . } Latest value is received
State Flow Conflation val stateFlow = MutableStateFlow( . .. )
stateFlow.value = UIState.Success( ... ) stateFlow.value = UIState.Error( .. . ) Conflate
State Flow Conflation val stateFlow = MutableStateFlow( . .. )
stateFlow.value = UIState.Success( ... ) stateFlow.value = UIState.Error( .. . ) stateFlow.collect { .. . } Error
State Flow View View Model State
State Flow State Flow Flow 1 Flow 2 Flow 3
Combined Flow
Flow Combine 1 A 1A Flow 1 Flow 2 Combined
Flow Combine 1 2 A 1A 2A Flow 1 Flow
2 Combined
Flow Combine 1 2 A 1A 2A Flow 1 Flow
2 Combined B 2B
val stateFlow = MutableStateFlow(UIState.Loading) flow1.combine(flow2) { a, b -
> } State Flow
val stateFlow = MutableStateFlow(UIState.Loading) flow1.combine(flow2) { a, b -
> combineItems(a, b) } State Flow
val stateFlow = MutableStateFlow(UIState.Loading) flow1.combine(flow2) { a, b -
> combineItems(a, b) }.collect { stateFlow.emit(it) } State Flow
Flow Marbles
State Flow View View Model State
Cash App - Molecule
Molecule Purpose Build a StateFlow using Jetpack Compose
Approach View Molecule Presenter (Composable) Events
Presenter @Composable fun Presenter(eventFlow: Flow<Event>): UiState { val
event by eventFlow.collectAsState(null) return if (event = = null) { UiState.Loading } else { UiState.Data(…) } }
Presenter @Composable fun Presenter(eventFlow: Flow<Event>): UiState { val
event by eventFlow.collectAsState(null) return if (event = = null) { UiState.Loading } else { UiState.Data(…) } }
Presenter @Composable fun Presenter(eventFlow: Flow<Event>): UiState { val
event by eventFlow.collectAsState(null) return if (event = = null) { UiState.Loading } else { UiState.Data(…) } }
Setup Molecule Presenter (Composable)
Setup Molecule Presenter (Composable) StateFlow
Launching Molecule val scope = CoroutineScope(Dispatchers.Main) val models: StateFlow<UsersModel> =
scope.launchMolecule { userPresenter(postsFlow, likesFlow) }
Launching Molecule val flow: StateFlow<UiState> = scope.launchMolecule { presenter(eventFlow) }
Setup View Molecule
Setup View View Model
View Model class MyViewModel: ViewModel() { val stateFlow
= moleculeScope.launchMolecule { val event by eventFlow.collectAsState(null) return if (event == null) { UiState.Loading } else { UiState.Success(…) } }
Learn More https: / / youtu.be/rUpZSZedoHI
State Flow • Different ways to create state flows •
Emit, collect
Shared Flow
Shared Flow
Shared Flow Consumer 1 Consumer 2
Shared Flow Consumer 1 Consumer 2
Shared Flow Consumer 1 Consumer 2 Event Event
Shared Flow Consumer 1 Consumer 2 Replay Replay
Shared Flow Buffer
Shared Flow val flow = MutableSharedFlow<String>()
Shared Flow val flow = MutableSharedFlow<String>() launch { flow.collect {
} }
Shared Flow val flow = MutableSharedFlow<String>() launch { flow.emit("Event
1") } launch { flow.collect { } }
Shared Flow val flow = MutableSharedFlow<String>() launch { flow.emit("Event
1") } launch { flow.collect { } } Event 1
Shared Flow val flow = MutableSharedFlow<String>() launch { flow.emit("Event
1”) } launch { delay(2000); flow.collect { } }
Shared Flow val flow = MutableSharedFlow<String>() launch { delay(2000);
flow.collect { } } launch { flow.emit("Event 1”) }
Shared Flow val flow = MutableSharedFlow<String>() launch { delay(2000);
flow.collect { } } launch { flow.emit("Event 1”) }
Shared Flow val flow = MutableSharedFlow<String>() launch { delay(2000);
flow.collect { } } No value is received launch { flow.emit("Event 1”) }
Shared Flow val flow = MutableSharedFlow<String>(replay = 1) launch
{ flow.emit("Event 1”) } launch { delay(2000); flow.collect { } }
Shared Flow val flow = MutableSharedFlow<String>(replay = 1) launch
{ delay(2000); flow.collect { } } launch { flow.emit("Event 1”) } Event 1
Shared Flow val flow = MutableSharedFlow<String>(replay = 1) Shared Flow
does not complete normally launch { flow.collect { } }
Cold Flows val flow = flowOf(1, 2, 3) flow
.onCompletion { } .collect { ... } Flow completes normally
Shared Flow val flow = MutableSharedFlow<String>(replay = 1) val job
= launch { flow.collect { } } job.cancel()
Shared Flow val flow = MutableSharedFlow<String>(replay = 1) val job
= launch { flow.onCompletion { }.collect { } } job.cancel() Flow completes exceptionally
Shared Flow • Setup • Replay and emit • Cancellation
Broadcast Channel vs Shared Flow
Broadcast Channel Shared Flow Channel APIs Replay Buffer Closed
val channel = BroadcastChannel<Int>(10) Broadcast Channel
val channel = BroadcastChannel<Int>(10) channel.send( ... ) Broadcast Channel
val channel = BroadcastChannel<Int>(10) channel.send( ... ) channel.close() Broadcast Channel
val flow = MutableSharedFlow() flow.emit( ... ) Shared Flow
Broadcast Channel Shared Flow Channel APIs Replay Buffer Closed
val flow = MutableSharedFlow(replay = 2) flow.emit( ... ) Shared
Flow
Broadcast Channel Shared Flow Channel APIs Replay Buffer Closed
val channel = BroadcastChannel<Int>(capacity = 10) channel.send( ... ) Broadcast
Channel
val flow = MutableSharedFlow( replay = 2, extraBufferCapacity = 10
) flow.emit( ... ) Shared Flow
Broadcast Channel Shared Flow Channel APIs Replay Buffer Closed
Broadcast Channel Shared Flow
val channel = BroadcastChannel<Int>(capacity) val flow = MutableSharedFlow<String>(extraBufferCapacity)
channel.send( ... ) channel.trySend( .. . ) flow.emit( ... )
flow.tryEmit( ... )
Broadcast Channel Shared Flow Channel APIs Replay Buffer Closed
Flow Sharing Strategies
Cold Flow Hot Flow Convert
State Flow State Flow Flow 1 Flow 2 Flow 3
Combined Flow
Creating State & Shared Flows • shareIn • stateIn
Sharing Policies • While Subscribed • Eagerly • Lazily
Sharing Policies flow.shareIn( )
Sharing Policies flow.shareIn( externalScope, )
Sharing Policies flow.shareIn( externalScope, replay = 1, )
Sharing Policies flow.shareIn( externalScope, replay = 1, started = SharingStarted.WhileSubscribed()
)
Sharing Policies val sharedFlow = flow.shareIn( externalScope, replay = 1,
started = SharingStarted.WhileSubscribed() )
Properties • Active as long as external scope is alive
• Remains as long as there are collectors.
Properties Active as long as external scope is alive externalScope.launch
{ sharedFlow.collect { } }
flow.shareIn( externalScope, replay = 1, started = SharingStarted.WhileSubscribed() ) Properties
Active as long as external scope is alive
Properties Active as long as external scope is alive externalScope.cancel()
externalScope.launch { sharedFlow.collect { } }
Properties Active as long as external scope is alive externalScope.cancel()
externalScope.launch { sharedFlow.collect { } } Complete Exceptionally
Properties Active as long as there are collectors.
Properties Active as long as there are collectors. val sharedFlow
= flow.onCompletion { }.shareIn(…)
Properties Active as long as there are collectors. val sharedFlow
= flow.onCompletion { }.shareIn(…) val job = launch { sharedFlow.onCompletion { }.collect { } }
Properties Active as long as there are collectors. val sharedFlow
= flow.onCompletion { }.shareIn(…) val job = launch { sharedFlow.onCompletion { }.collect { } } job.cancel()
Properties Active as long as there are collectors. val sharedFlow
= flow.onCompletion { }.shareIn(…) val job = launch { sharedFlow.onCompletion { }.collect { } } job.cancel()
Properties Active as long as there are collectors. val sharedFlow
= flow.onCompletion { }.shareIn(…) val job = launch { sharedFlow.onCompletion { }.collect { } } job.cancel()
Properties Active as long as there are collectors. val sharedFlow
= flow.onCompletion { }.shareIn(…) val job1 = launch { sharedFlow.collect { } } val job2 = launch { sharedFlow.collect { } }
Properties Active as long as there are collectors. val sharedFlow
= flow.onCompletion { }.shareIn(…) job1.cancel() val job2 = launch { sharedFlow.collect { } }
Properties Active as long as there are collectors. val sharedFlow
= flow.onCompletion { }.shareIn(…) job1.cancel() val job2 = launch { sharedFlow.collect { } } Remain Active
Properties • Active as long as external scope is alive
• Active as long as there are collectors.
Sharing Policies • While Subscribed • Eagerly • Lazily
Eagerly flow.shareIn( externalScope, replay = 1, started = SharingStarted.Eagerly() )
Eagerly Start producer eagerly flow .onStart { println("ON START") }
.shareIn( ... started = SharingStarted.Eagerly)
Eagerly Start producer eagerly flow .onStart { println("ON START") }
.shareIn( ... started = SharingStarted.Eagerly)
Eagerly Start producer eagerly flow .onStart { println("ON START") }
.shareIn( ... started = SharingStarted.Eagerly) // ON START
Eagerly Start producer eagerly
Sharing Policies • While Subscribed • Eagerly • Lazily
Lazily Start sharing after the first subscriber appears
Lazily flow.shareIn( externalScope, replay = 1, started = SharingStarted.Lazily )
Lazily flow .onStart { println("ON START") } .shareIn(…,started = SharingStarted.Lazily)
Lazily flow .onStart { println("ON START") } .shareIn(…,started = SharingStarted.Lazily)
launch { sharedFlow.collect { } }
Lazily flow .onStart { println("ON START") } .shareIn(…,started = SharingStarted.Lazily)
launch { sharedFlow.collect { } } // ON START
Lazily Start sharing after the first subscriber appears
Sharing Policies • While Subscribed • Active while there are
active subscribers. • Eagerly • Start producer eagerly and never stop • Lazily • Start after the first subscriber appears and never stop
Manage Backpressure
Shared Flow Buffer
Shared Flow Producer Consumer
Shared Flow Producer Consumer Generating events fast
Shared Flow Producer Consumer Listening to events with
delay
Shared Flow Producer Consumer
Shared Flow Producer Consumer
Shared Flow Producer Consumer What happens when it is
full?
Buffering Overflow Strategies • Suspend • Drop oldest • Drop
latest
Shared Flow Producer Consumer Suspend
Buffering Overflow Strategies val flow = MutableSharedFlow<String>( extraBufferCapacity = 2,
onBufferOverflow = BufferOverflow.SUSPEND ) Buffer + Replay Count
Buffering Overflow Strategies val flow = MutableSharedFlow<String>( extraBufferCapacity = 2,
onBufferOverflow = BufferOverflow.SUSPEND )
Buffering Overflow Strategies launch { flow.emit("Event 1") flow.emit("Event 2") flow.emit("Event
3") } Suspend
Buffering Overflow Strategies • Suspend • Drop oldest • Drop
latest
Shared Flow Producer Consumer Drop Oldest
Shared Flow Producer Consumer Drop latest
Buffering Overflow Strategies • Suspend • Drop oldest • Drop
latest
Kotlin State & Shared Flows in Action • State &
Shared Flow APIs • Migrating from broadcast channels • Flow Sharing Strategies • Manage Backpressure
Thank You! www.codingwithmohit.com @heyitsmohit