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
Kotlin State & Shared Flows in Action
Search
Mohit S
July 27, 2021
Programming
4
1.3k
Kotlin State & Shared Flows in Action
Shared Flow APIs
Mohit S
July 27, 2021
Tweet
Share
More Decks by Mohit S
See All by Mohit S
Guide to Improving Compose Performance
heyitsmohit
0
240
Building Shared UIs across Platforms with Compose
heyitsmohit
1
630
Building Multiplatform Apps with Compose
heyitsmohit
2
510
Building StateFlows with Jetpack Compose
heyitsmohit
6
1.9k
Building Android Testing Infrastructure
heyitsmohit
1
490
Migrating to Kotlin State & Shared Flows
heyitsmohit
1
790
Using Square Workflow for Android & iOS
heyitsmohit
1
430
Building Android Infrastructure Teams at Scale
heyitsmohit
3
330
Strategies for Migrating to Jetpack Compose
heyitsmohit
2
570
Other Decks in Programming
See All in Programming
レガシープロジェクトで最大限AIの恩恵を受けられるようClaude Codeを利用する
tk1351
4
1.6k
CloudflareのChat Agent Starter Kitで簡単!AIチャットボット構築
syumai
2
340
TanStack DB ~状態管理の新しい考え方~
bmthd
2
420
個人軟體時代
ethanhuang13
0
290
Processing Gem ベースの、2D レトロゲームエンジンの開発
tokujiros
2
120
時間軸から考えるTerraformを使う理由と留意点
fufuhu
9
3.8k
MCPで実現するAIエージェント駆動のNext.jsアプリデバッグ手法
nyatinte
7
1k
Laravel Boost 超入門
fire_arlo
2
180
プロポーザル駆動学習 / Proposal-Driven Learning
mackey0225
1
330
JSONataを使ってみよう Step Functionsが楽しくなる実践テクニック #devio2025
dafujii
0
240
Google I/O recap web編 大分Web祭り2025
kponda
0
2.9k
MCPとデザインシステムに立脚したデザインと実装の融合
yukukotani
3
1k
Featured
See All Featured
No one is an island. Learnings from fostering a developers community.
thoeni
21
3.4k
A better future with KSS
kneath
239
17k
Designing Dashboards & Data Visualisations in Web Apps
destraynor
231
53k
Optimizing for Happiness
mojombo
379
70k
Measuring & Analyzing Core Web Vitals
bluesmoon
9
570
Put a Button on it: Removing Barriers to Going Fast.
kastner
60
4k
The Art of Delivering Value - GDevCon NA Keynote
reverentgeek
15
1.6k
The Cost Of JavaScript in 2023
addyosmani
53
8.9k
[RailsConf 2023] Rails as a piece of cake
palkan
56
5.8k
Helping Users Find Their Own Way: Creating Modern Search Experiences
danielanewman
29
2.8k
[Rails World 2023 - Day 1 Closing Keynote] - The Magic of Rails
eileencodes
36
2.5k
Bootstrapping a Software Product
garrettdimon
PRO
307
110k
Transcript
Mohit Sarveiya Kotlin State & Shared Flows in Action @heyitsmohit
Kotlin State & Shared Flows in Action • State Flow
• Shared Flow • Broadcast Channel vs shared flow • Convert cold streams to shared flows • Buffer Overflow Strategies
Cold vs Hot Flows
What is a cold stream? A cold stream is a
flow that triggers the same code every time it is collected.
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 { // 2, 3, 4 }
What is a hot stream? A hot stream is a
flow whose active instance exists independently of the presence of collectors.
Hot Streams State Flow Shared Flow
State Flow View View Model
State Flow View View Model
State Flow View View Model State
State Flow sealed class UiState { data class Error(
val exception: Throwable ): UiState() }
State Flow sealed class UiState { data class Success(
val data: Data ): UiState() data class Error( val exception: Throwable ): UiState() }
State Flow sealed class UiState { data class Success(
val data: Data ): UiState() data class Error( val exception: Throwable ): UiState() }
State Flow val uiState = MutableStateFlow()
val uiState = MutableStateFlow( UiState.Success(Data()) ) State Flow
State Flow val uiState = MutableStateFlow( . .. ) uiState.emit(
UIState.Success(Data()) )
State Flow val uiState = MutableStateFlow( . .. ) uiState.value
= UIState.Success(Data())
State Flow val uiState = MutableStateFlow( . .. ) uiState.collect
{ ... } Latest value is received
State Flow val uiState = MutableStateFlow( . .. ) uiState.collect
{ ... } uiState.collect { ... } Latest value is received
State Flow Conflation val uiState = MutableStateFlow( . .. )
uiState.value = UIState.Success( .. . ) uiState.value = UIState.Error( .. . ) Conflate
State Flow Conflation val uiState = MutableStateFlow( . .. )
uiState.value = UIState.Success( .. . ) uiState.value = UIState.Error( .. . ) uiState.collect { ... } Error
State Flow vs Live Data State Flow Live Data Default
Value Unsubscribe (Stopped State)
State Flow vs Live Data State Flow Live Data Default
Value Unsubscribe (Stopped State)
State Flow vs Live Data State Flow Live Data Default
Value Unsubscribe (Stopped State)
State Flow Summary • How to setup state flow •
Emit and collect • State Flow vs Live Data
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 < > ()
Shared Flow val flow = MutableSharedFlow<String>()
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>() launch { flow.emit("Event
1”) } launch { delay(2000); flow.collect { } } Replay
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
val flow = MutableSharedFlow<String>(replay = 1) Shared Flow State
Flow launch { flow.collect { } } launch { flow.subscriptionCount.value }
Shared Flow val flow = MutableSharedFlow<String>(replay = 1) 1 Subscriber
launch { flow.collect { } } launch { flow.subscriptionCount.value }
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 Summary • Setup • Replay and emit •
Cancellation
Broadcast Channel vs Shared Flow
Broadcast Channel Shared Flow Channel APIs Replay Buffer Closed
val channel = BroadcastChannel<Int>(10)
val channel = BroadcastChannel<Int>(10) channel.send( ... )
val channel = BroadcastChannel<Int>(10) channel.send( ... ) channel.close()
val stateFlow = MutableSharedFlow() stateFlow.emit( ... )
Broadcast Channel Shared Flow Channel APIs Replay Buffer Closed
val stateFlow = MutableSharedFlow(replay = 2) stateFlow.emit( ... )
Broadcast Channel Shared Flow Channel APIs Replay Buffer Closed
val channel = BroadcastChannel<Int>(capacity = 10) channel.send( ... )
val stateFlow = MutableSharedFlow( replay = 2, extraBufferCapacity = 10
) stateFlow.emit( ... )
Broadcast Channel Shared Flow Channel APIs Replay Buffer Closed
val channel = BroadcastChannel<Int>(10) channel.send( ... ) channel.close()
val stateFlow = MutableSharedFlow( replay = 2, extraBufferCapacity = 10
) stateFlow.emit( ... )
Broadcast Channel Shared Flow Channel APIs Replay Buffer Closed
Broadcast Channel Shared Flow
val channel = BroadcastChannel<Int>(capacity)
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
Sharing Policies • While Subscribed • Eagerly • Lazily
Sharing Policies flow
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() )
While Subscribed • Active as long as external scope is
alive • Remains as long as there are collectors.
Properties Active as long as external scope is alive
Properties Active as long as external scope is alive sharedFlow.collect
{ } Subscriber
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 sharedFlow.collect
{ } externalScope.cancel()
Properties Active as long as external scope is alive sharedFlow.collect
{ } externalScope.cancel() Complete Exceptionally
Properties Remains as long as there are collectors.
Properties Remains as long as there are collectors. val sharedFlow
= flow.onCompletion { }.shareIn(…)
Properties Remains as long as there are collectors. val sharedFlow
= flow.onCompletion { }.shareIn(…) val job = launch { sharedFlow.onCompletion { }.collect { } }
Properties Remains as long as there are collectors. val sharedFlow
= flow.onCompletion { }.shareIn(…) val job = launch { sharedFlow.onCompletion { }.collect { } } job.cancel()
Properties Remains as long as there are collectors. val sharedFlow
= flow.onCompletion { }.shareIn(…) val job = launch { sharedFlow.onCompletion { }.collect { } } job.cancel()
Properties Remains as long as there are collectors. val sharedFlow
= flow.onCompletion { }.shareIn(…) val job = launch { sharedFlow.onCompletion { }.collect { } } job.cancel()
Properties Remains as long as there are collectors. val sharedFlow
= flow.onCompletion { }.shareIn(…) val job1 = launch { sharedFlow.collect { } } val job2 = launch { sharedFlow.collect { } }
Properties Remains as long as there are collectors. val sharedFlow
= flow.onCompletion { }.shareIn(…) job1.cancel() val job2 = launch { sharedFlow.collect { } }
Properties Remains 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
• Remains 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 and never stop flow .onStart {
println("ON START") } .shareIn( ... started = SharingStarted.Eagerly)
Eagerly Start producer eagerly and never stop flow .onStart {
println("ON START") } .shareIn( ... started = SharingStarted.Eagerly)
Eagerly Start producer eagerly and never stop flow .onStart {
println("ON START") } .shareIn( ... started = SharingStarted.Eagerly) ON START
Eagerly Start producer eagerly and never stop flow .onComplete {
println("ON COMPLETE”) } .shareIn( ... started = SharingStarted.Eagerly)
Eagerly Start producer eagerly and never stop flow .onComplete {
println("ON COMPLETE”) } .shareIn( ... started = SharingStarted.Eagerly) externalScope.cancel()
Eagerly Start producer eagerly and never stop flow .onComplete {
println("ON COMPLETE”) } .shareIn( ... started = SharingStarted.Eagerly) Never stops externalScope.cancel()
Eagerly Start producer eagerly and never stop
Sharing Policies • While Subscribed • Eagerly • Lazily
Lazily Start sharing after the first subscriber appears and never
stop
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 flow .onCompletion { println("COMPLETE") } .shareIn(…,started = SharingStarted.Lazily)
flow .onCompletion { println("COMPLETE") } .shareIn(externalScope,…,started = SharingStarted.Lazily) Lazily
flow .onCompletion { println("COMPLETE") } .shareIn(externalScope,…,started = SharingStarted.Lazily) Lazily externalScope.cancel()
flow .onCompletion { println("COMPLETE") } .shareIn(externalScope,…,started = SharingStarted.Lazily) Lazily Never
stops externalScope.cancel()
Lazily Start sharing after the first subscriber appears and never
stop
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
Buffer Overflow Strategies
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 Flow
• Shared Flow • Broadcast Channel vs shared flow • Convert cold streams to shared flows • Buffer Overflow Strategies
https: // codingwithmohit.com/coroutines/learning-shared-and-state-flows-with-tests/ Coding with Mohit
Thank You! www.codingwithmohit.com @heyitsmohit