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Flowing in the Deep
Exploring Event Streams in Kotlin
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No content
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Hannes Dorfmann
sockeqwe
Gabriel Ittner
gabrielittner
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No content
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W
FL
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Flowing in the Deep
• Introduction
• Operators
• Threading
• Useful APIs
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fun doHttpRequest() : X {
// A long running operation
...
return X
}
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class MyActivity : Activity() {
override fun onCreate(b: Bundle) {
doHttpRequest()
}
}
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class MyActivity : Activity() {
override fun onCreate(b: Bundle) {
doHttpRequest()
}
}
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class MyActivity : Activity() {
override fun onCreate(b: Bundle) {
thread {
doHttpRequest()
}
}
}
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class MyActivity : Activity() {
override fun onCreate(b: Bundle) {
thread {
val x = doHttpRequest()
???
}
}
}
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fun doHttpRequest() : X {
// A long running operation
...
return X
}
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fun doHttpRequest( callback: (X) -> Unit ){
// A long running operation
...
callback(X)
}
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fun doHttpRequest( callback: (X) -> Unit ){
thread {
// A long running operation
...
callback(X)
}
}
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class MyActivity : Activity() {
override fun onCreate(b: Bundle) {
doHttpRequest { result ->
// do something with the result
}
}
}
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doHttpRequest {
...
}
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doHttpRequest {
doHttpRequest {
...
}
}
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doHttpRequest {
doHttpRequest {
doHttpRequest {
...
}
}
}
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doHttpRequest {
doHttpRequest {
doHttpRequest {
doHttpRequest {
...
}
}
}
}
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doHttpRequest {
doHttpRequest {
doHttpRequest {
doHttpRequest {
doHttpRequest {
...
}
}
}
}
}
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doHttpRequest {
doHttpRequest {
doHttpRequest {
doHttpRequest {
doHttpRequest {
doHttpRequest {
...
}
}
}
}
}
}
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doHttpRequest {
doHttpRequest {
doHttpRequest {
doHttpRequest {
doHttpRequest {
doHttpRequest {
doHttpRequest {
...
}
}
}
}
}
}
}
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Callback Hell
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fun doHttpRequest( callback: (X) -> Unit ) {
// A long running operation
...
callback(X)
}
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suspend fun doHttpRequest(): X {
// A long running operation
...
return X
}
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launch {
val a = doHttpRequest()
val b = doHttpRequest()
val c = doHttpRequest()
val d = doHttpRequest()
val e = doHttpRequest()
val f = doHttpRequest()
val g = doHttpRequest()
}
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suspend fun doHttpRequest(): X {
// A long running operation
...
return X
}
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fun doHttpRequest(continuation : Continuation) {
// A long running operation
...
}
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fun doHttpRequest(continuation : Continuation) {
// A long running operation
...
contination.resume(X)
}
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fun doHttpRequest( callback: (X) -> Unit ){
// A long running operation
...
callback(X)
}
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fun doHttpRequest( observer: (X) -> Unit ){
// A long running operation
...
observer(X)
}
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Observer Pattern
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fun doHttpRequest( observer: (X) -> Unit ){
// A long running operation
...
observer(X)
}
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fun downloadVideo( observer: (progress) -> Unit ) {
}
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fun downloadVideo( observer: (progress) -> Unit ) {
// A long running operation
...
observer(0.1)
...
observer(0.2)
...
observer(1.0)
}
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suspend fun downloadVideo() : ??? {
// A long running operation
...
???
}
With Coroutines?
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fun downloadVideo( observer: (progress) -> Unit )
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interface Downloader {
fun downloadVideo( observer: (progress) -> Unit )
}
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interface Downloader {
fun download( observer: (progress) -> Unit )
}
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interface Downloader {
fun download( observer: (T) -> Unit )
}
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interface Downloader {
fun download( observer: (T) -> Unit )
}
interface DownloadObserver
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interface Downloader {
fun download( observer: (T) -> Unit )
}
interface DownloadObserver {
fun emit( value: T )
}
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interface Downloader {
fun download( o: DownloadObserver )
}
interface DownloadObserver {
fun emit( value: T )
}
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interface Downloader {
fun download( o: DownloadObserver )
}
interface DownloadObserver {
fun emit( value: T )
}
interface Downloader {
fun download( o: DownloadObserver )
}
interface DownloadObserver {
fun emit( value: T )
}
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interface Downloader {
fun download( o: DownloadObserver )
}
interface DownloadObserver {
fun emit( value: T )
}
interface Downloader {
fun collect( o: DownloadObserver )
}
interface DownloadObserver {
fun emit( value: T )
}
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interface Downloader {
fun download( o: DownloadObserver )
}
interface DownloadObserver {
fun emit( value: T )
}
interface Downloader {
fun collect( c: Collector )
}
interface Collector {
fun emit( value: T )
}
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interface Downloader {
fun download( o: DownloadObserver )
}
interface DownloadObserver {
fun emit( value: T )
}
interface Flow {
fun collect( c: Collector )
}
interface Collector {
fun emit( value: T )
}
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interface Downloader {
fun download( o: DownloadObserver )
}
interface DownloadObserver {
fun emit( value: T )
}
interface Flow {
fun collect( c: FlowCollector )
}
interface FlowCollector {
fun emit( value: T )
}
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interface Flow {
fun collect( c: FlowCollector )
}
interface FlowCollector {
fun emit( value: T )
}
Flow
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interface Flow {
suspend fun collect( c: FlowCollector )
}
interface FlowCollector {
suspend fun emit( value: T )
}
Flow
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fun downloadVideo(): ??? {
...
???
}
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fun downloadVideo(): Flow {
...
???
}
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fun flow(block: suspend FlowCollector.() -> Unit): Flow
fun downloadVideo(): Flow {
...
???
}
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fun flow(block: suspend FlowCollector.() -> Unit): Flow
fun downloadVideo(): Flow = flow {
...
???
}
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fun flow(block: suspend FlowCollector.() -> Unit): Flow
fun downloadVideo(): Flow = flow {
// this: FlowCollector
...
???
}
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fun flow(block: suspend FlowCollector.() -> Unit): Flow
fun downloadVideo(): Flow = flow {
// this: FlowCollector
...
emit(0.1)
}
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fun flow(block: suspend FlowCollector.() -> Unit): Flow
fun downloadVideo(): Flow = flow {
// this is FlowCollector
...
emit(0.1)
...
emit(0.2)
...
emit(1.0)
}
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Let it Flow!
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flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}
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class MyViewModel : ViewModel() {
init {
viewModelScope.launch {
flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}
}
}
}
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class MyViewModel : ViewModel() {
init {
viewModelScope.launch {
flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}
}
}
}
Launch new coroutine
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class MyViewModel : ViewModel() {
init {
viewModelScope.launch {
flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}
}
}
}
Launch new coroutine
2.1.0-beta01
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class MyViewModel : ViewModel() {
init {
viewModelScope.launch {
flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}
}
}
}
Suspending block
executed in coroutine
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launch {
flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}
}
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launch {
flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}.collect { value ->
println(value)
}
}
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launch {
flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}.collect { value ->
println(value)
}
}
Observes flow
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launch {
flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}.collect { value ->
println(value)
}
}
notify observer
about value
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launch {
flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}.collect { value ->
println(value)
}
}
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What about errors?
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flow {
throw Exception("Something went wrong")
}.collect {
println(it)
}
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flow {
throw Exception("Something went wrong")
}.collect {
println(it)
}
re-throws
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try {
flow {
throw Exception("Something went wrong")
}.collect {
println(it)
}
} catch (e: Exception) {
// handle error
}
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flow {
emit(0.1)
throw Exception("Something went wrong")
}.collect {
println(it)
}
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flow {
emit(0.1)
throw Exception("Something went wrong")
}.collect {
println(it)
}
sealed class DownloadStatus {
}
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flow {
emit(0.1)
throw Exception("Something went wrong")
}.collect {
println(it)
}
sealed class DownloadStatus {
data class Progress(val value: Double) : DownloadStatus()
object Success : DownloadStatus()
data class Error(val message: String) : DownloadStatus()
}
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flow {
emit(DownloadStatus.Progress(0.1))
try {
throw IOException(“Something went wrong”))
} catch (e: IOException) {
emit(DownloadStatus.Error(e.message))
}
}.collect {
println(it)
}
sealed class DownloadStatus {
data class Progress(val value: Double) : DownloadStatus()
object Success : DownloadStatus()
data class Error(val message: String) : DownloadStatus()
}
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And completion?
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launch {
flow {
// do stuff
}.collect { value ->
println(value)
}
}
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launch {
flow {
// do stuff
}.collect { value ->
println(value)
}
}
Flow gets
instantiated
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launch {
flow {
// do stuff
}.collect { value ->
println(value)
}
}
collect gets called
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launch {
flow {
// do stuff
}.collect { value ->
println(value)
}
}
coroutine
suspends here
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launch {
flow {
// do stuff
}.collect { value ->
println(value)
}
}
executed
collect
suspends here
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launch {
flow {
// do stuff
}.collect { value ->
println(value)
}
}
called for
emission
collect
suspends here
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launch {
flow {
// do stuff
}.collect { value ->
println(value)
}
}
executed
collect
suspends here
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launch {
flow {
// do stuff
}.collect { value ->
println(value)
}
}
called for
emission
collect
suspends here
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launch {
flow {
// do stuff
}.collect { value ->
println(value)
}
}
collect
suspends here
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launch {
flow {
// do stuff
}.collect { value ->
println(value)
}
}
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launch {
flow {
// do stuff
}.collect { value ->
println(value)
}
handleCompletion()
}
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flow {
// do stuff
}.onCompletion {
handleCompletion()
}.collect { value ->
println(value)
}
new
in
1.3.0-M
2
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Operator
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flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}.map { value ->
value * 2
}.collect { value ->
println(value)
}
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fun Flow.map(transformer: suspend (value: T) -> R): Flow {
}
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fun Flow.map(transformer: suspend (value: T) -> R): Flow {
return flow {
}
}
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fun Flow.map(transformer: suspend (value: T) -> R): Flow {
return flow { // this: FlowCollector
}
}
fun flow(block: suspend FlowCollector.() -> Unit): Flow
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fun Flow.map(transformer: suspend (value: T) -> R): Flow {
return flow { // this: FlowCollector
}
}
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fun Flow.map(transformer: suspend (value: T) -> R): Flow {
return flow { // this: FlowCollector
collect { value ->
}
}
}
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fun Flow.map(transformer: suspend (value: T) -> R): Flow {
return flow { // this: FlowCollector
collect { value ->
}
}
}
Flow.collect
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fun Flow.map(transformer: suspend (value: T) -> R): Flow {
return flow { // this: FlowCollector
collect { value ->
}
}
}
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flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}.map { value ->
value * 2
}.collect { value ->
println(value)
}
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flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}.map { value ->
value * 2
}.collect { value ->
println(value)
}
fun Flow.map(…)
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flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}.map { value ->
value * 2
}.collect { value ->
println(value)
}
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flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}.map { value ->
value * 2
}.collect { value ->
println(value)
}
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fun Flow.map(transformer: suspend (value: T) -> R): Flow {
return flow { // this: FlowCollector
collect { value ->
}
}
}
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fun Flow.map(transformer: suspend (value: T) -> R): Flow {
return flow { // this: FlowCollector
collect { value ->
}
}
}
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fun Flow.map(transformer: suspend (value: T) -> R): Flow {
return flow { // this: FlowCollector
collect { value ->
val r = transformer(value)
}
}
}
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fun Flow.map(transformer: suspend (value: T) -> R): Flow {
return flow { // this: FlowCollector
collect { value ->
val r = transformer(value)
emit(r)
}
}
}
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fun Flow.map(transformer: suspend (value: T) -> R): Flow {
return flow { // this: FlowCollector
collect { value ->
val r = transformer(value)
emit(r)
}
}
}
FlowCollector.emit(value)
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flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}.map { value ->
value * 2
}.collect { value
println(value)
}
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Operator
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Operator
Observer Pattern
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flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}.switchMap { value ->
flow {
emit(“first $value")
delay(500)
emit(“second $value")
}
}.collect { value ->
println(value)
}
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flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}.switchMap { value ->
flow {
emit(“first $value")
delay(500)
emit(“second $value")
}
}.collect { value ->
println(value)
}
Console output
first 0
first 1
first 2
first 3
first 4
first 5
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fun Flow.switchMap(
mapper: suspend (value: T) -> Flow
): Flow {
}
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fun Flow.switchMap(
mapper: suspend (value: T) -> Flow
): Flow {
return flow {
}
}
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fun Flow.switchMap(
mapper: suspend (value: T) -> Flow
): Flow {
return flow {
collect { outerValue ->
}
}
}
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fun Flow.switchMap(
mapper: suspend (value: T) -> Flow
): Flow {
return flow {
collect { outerValue ->
}
}
}
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flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}.switchMap { value
flow {
emit(“first $value")
delay(500)
emit(“second $value")
}
}.collect { value ->
println(value)
}
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flow {
for (i in 0..5) {
delay(100)
emit(i)
}
}.switchMap { value ->
flow {
emit(“first $value")
delay(500)
emit(“second $value")
}
}.collect { value
println(value)
}
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fun Flow.switchMap(
mapper: suspend (value: T) -> Flow
): Flow {
return flow {
collect { outerValue ->
}
}
}
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fun Flow.switchMap(
mapper: suspend (value: T) -> Flow
): Flow {
return flow {
collect { outerValue ->
val inner : Flow = mapper(outerValue)
}
}
}
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fun Flow.switchMap(
mapper: suspend (value: T) -> Flow
): Flow {
return flow {
collect { outerValue ->
val inner : Flow = mapper(outerValue)
inner.collect { value ->
}
}
}
}
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fun Flow.switchMap(
mapper: suspend (value: T) -> Flow
): Flow {
return flow {
collect { outerValue ->
val inner : Flow = mapper(outerValue)
launch {
inner.collect { value ->
}
}
}
}
}
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fun Flow.switchMap(
mapper: suspend (value: T) -> Flow
): Flow {
return flow {
collect { outerValue ->
val inner : Flow = mapper(outerValue)
launch {
inner.collect { value ->
emit(value)
}
}
}
}
}
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fun Flow.switchMap(
mapper: suspend (value: T) -> Flow
): Flow {
return flow { // this: FlowCollector
collect { outerValue ->
val inner : Flow = mapper(outerValue)
launch {
inner.collect { value ->
emit(value)
}
}
}
}
}
FlowCollector.emit(value)
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fun Flow.switchMap(
mapper: suspend (value: T) -> Flow
): Flow {
return flow {
collect { outerValue ->
val inner : Flow = mapper(outerValue)
launch {
inner.collect { value ->
emit(value)
}
}
}
}
}
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fun Flow.switchMap(
mapper: suspend (value: T) -> Flow
): Flow {
return flow {
var currentJob: Job? = null
collect { outerValue ->
val inner : Flow = mapper(outerValue)
currentJob = launch {
inner.collect { value ->
emit(value)
}
}
}
}
}
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fun Flow.switchMap(
mapper: suspend (value: T) -> Flow
): Flow {
return flow {
var currentJob: Job? = null
collect { outerValue ->
val inner : Flow = mapper(outerValue)
currentJob?.cancelAndJoin()
currentJob = launch {
inner.collect { value ->
emit(value)
}
}
}
}
}
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fun Flow.switchMap(
mapper: suspend (value: T) -> Flow
): Flow {
return flow {
coroutineScope {
var currentJob: Job? = null
collect { outerValue ->
val inner : Flow = mapper(outerValue)
currentJob?.cancelAndJoin()
currentJob = launch {
inner.collect { value ->
emit(value)
}
}
}
}
}
}
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Threading
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interface CoroutineContext
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interface CoroutineContext
interface Job : CoroutineContext {
public fun cancel(): Unit
// a lot more…
}
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interface CoroutineContext
interface Job : CoroutineContext {
public fun cancel(): Unit
// a lot more…
}
abstract class CoroutineDispatcher
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interface CoroutineContext
interface Job : CoroutineContext {
public fun cancel(): Unit
// a lot more…
}
abstract class CoroutineDispatcher
Dispatchers.Main
Dispatchers.Default
Dispatchers.IO
Dispatchers.Unconfined
newSingleThreadContext()
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interface CoroutineContext
interface Job : CoroutineContext {
public fun cancel(): Unit
// a lot more…
}
abstract class CoroutineDispatcher
Dispatchers.Main
Dispatchers.Default
Dispatchers.IO
Dispatchers.Unconfined
newSingleThreadContext()
val context: CoroutineContext = Job() + Dispatchers.IO
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public interface CoroutineScope {
public val coroutineContext: CoroutineContext
}
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public interface CoroutineScope {
public val coroutineContext: CoroutineContext
}
public inline fun CoroutineScope.cancel()
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public interface CoroutineScope {
public val coroutineContext: CoroutineContext
}
public inline fun CoroutineScope.cancel()
public fun CoroutineScope.launch(...)
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public interface CoroutineScope {
public val coroutineContext: CoroutineContext
}
public inline fun CoroutineScope.cancel()
public fun CoroutineScope.launch(...)
val ViewModel.viewModelScope: CoroutineScope
val Lifecycle.coroutineScope: LifecycleCoroutineScope
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Threading
(actually)
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lifecycle.coroutineScope.launchWhenStarted {
}
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}.map {
it + 1
}.map {
it.toString()
}.collect {
println(it)
}
}
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}.map {
it + 1
}.map {
it.toString()
}.collect {
println(it)
}
}
main thread
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}.map {
it + 1
}.map {
it.toString()
}.collect {
println(it)
}
}
main thread
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}.map {
it + 1
}.map {
it.toString()
}.collect {
println(it)
}
}
main thread
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}.map {
it + 1
}.map {
it.toString()
}.collect {
println(it)
}
}
main thread
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}.map {
it + 1
}.map {
it.toString()
}.collect {
println(it)
}
}
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lifecycle.coroutineScope.launchWhenStarted {
flow {
GlobalScope.launch {
// expensive operation
emit(progress)
// expensive operation
emit(result)
}
}.map {
it + 1
}.map {
it.toString()
}.collect {
println(it)
}
}
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lifecycle.coroutineScope.launchWhenStarted {
flow {
withContext(Dispatchers.IO) {
// expensive operation
emit(progress)
// expensive operation
emit(result)
}
}.map {
it + 1
}.map {
it.toString()
}.collect {
println(it)
}
}
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lifecycle.coroutineScope.launchWhenStarted {
flow {
withContext(Dispatchers.IO) {
// expensive operation
emit(progress)
// expensive operation
emit(result)
}
}.map {
it + 1
}.map {
it.toString()
}.collect {
println(it)
}
}
IllegalStateException
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lifecycle.coroutineScope.launchWhenStarted {
flow {
withContext(Dispatchers.IO) {
// expensive operation
emit(progress)
// expensive operation
emit(result)
}
}.map {
it + 1
}.map {
it.toString()
}.collect {
println(it)
}
}
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lifecycle.coroutineScope.launchWhenStarted {
channelFlow {
withContext(Dispatchers.IO) {
// expensive operation
emit(progress)
// expensive operation
emit(result)
}
}.map {
it + 1
}.map {
it.toString()
}.collect {
println(it)
}
}
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lifecycle.coroutineScope.launchWhenStarted {
channelFlow { // this: ProducerScope
withContext(Dispatchers.IO) {
// expensive operation
emit(progress)
// expensive operation
emit(result)
}
}.map {
it + 1
}.map {
it.toString()
}.collect {
println(it)
}
}
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lifecycle.coroutineScope.launchWhenStarted {
channelFlow { // this: ProducerScope
withContext(Dispatchers.IO) {
// expensive operation
send(progress)
// expensive operation
send(result)
}
}.map {
it + 1
}.map {
it.toString()
}.collect {
println(it)
}
}
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lifecycle.coroutineScope.launchWhenStarted {
channelFlow { // this: ProducerScope
withContext(Dispatchers.IO) {
// expensive operation
send(progress)
// expensive operation
send(result)
}
}.map {
it + 1
}.map {
it.toString()
}.collect {
println(it)
}
}
main thread
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lifecycle.coroutineScope.launchWhenStarted {
channelFlow { // this: ProducerScope
withContext(Dispatchers.IO) {
// expensive operation
send(progress)
// expensive operation
send(result)
}
}.map {
it + 1
}.map {
it.toString()
}.collect {
println(it)
}
}
main thread
IO thread
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}.map {
it + 1
}.map {
it.toString()
}.collect {
println(it)
}
}
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}.map {
it + 1
}
.flowOn(Dispatchers.IO)
.map {
it.toString()
}.collect {
println(it)
}
}
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}.map {
it + 1
}
.flowOn(Dispatchers.IO)
.map {
it.toString()
}.collect {
println(it)
}
}
main thread
IO thread
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}.map {
it + 1
}
.flowOn(Dispatchers.IO)
.map {
it.toString()
}.collect {
println(it)
}
}
main thread
IO thread
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}.map {
it + 1
}
.flowOn(Dispatchers.IO)
.map {
it.toString()
}.collect {
println(it)
}
}
main thread
IO thread
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}.map {
it + 1
}
.flowOn(Dispatchers.IO)
.map {
it.toString()
}.collect {
println(it)
}
}
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}
.flowOn(Dispatchers.IO)
.map {
it + 1
}
.flowOn(Dispatchers.Default)
.map {
it.toString()
}.collect {
println(it)
}
}
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}
.flowOn(Dispatchers.IO)
.map {
it + 1
}
.flowOn(Dispatchers.Default)
.map {
it.toString()
}.collect {
println(it)
}
}
main thread
IO thread
Default thread
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}
.flowOn(Dispatchers.IO)
.map {
it + 1
}
.flowOn(Dispatchers.Default)
.map {
it.toString()
}.collect {
println(it)
}
}
main thread
IO thread
Default thread
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}
.flowOn(Dispatchers.IO)
.map {
it + 1
}
.flowOn(Dispatchers.Default)
.map {
it.toString()
}.collect {
println(it)
}
}
main thread
IO thread
Default thread
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lifecycle.coroutineScope.launchWhenStarted {
flow {
// expensive operation
}
.flowOn(Dispatchers.IO)
.map {
it + 1
}
.flowOn(Dispatchers.Default)
.map {
it.toString()
}.collect {
println(it)
}
}
main thread
IO thread
Default thread
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Threading
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Threading
• collect lambda is always called on the initial CoroutineContext
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Threading
• collect lambda is always called on the initial CoroutineContext
• flowOn does only influence the upstream
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Threading
• collect lambda is always called on the initial CoroutineContext
• flowOn does only influence the upstream
• nothing can change the context of downstream emissions
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Some useful APIs
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flowOf(1, 2, 3, 4)
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flowOf(1, 2, 3, 4)
listOf(1, 2, 3, 4).asFlow()
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flowOf(1, 2, 3, 4)
listOf(1, 2, 3, 4).asFlow()
sequenceOf(1, 2, 3, 4).asFlow()
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val someFunction: (() -> Result) = ...
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val someFunction: (() -> Result) = ...
someFunction.asFlow()
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val someFunction: (() -> Result) = ...
someFunction.asFlow()
val doHttpRequest: (suspend () -> Result) = ...
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val someFunction: (() -> Result) = ...
someFunction.asFlow()
val doHttpRequest: (suspend () -> Result) = ...
doHttpRequest.asFlow()
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val observable: Observable = Observable.just(1)
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val observable: Observable = Observable.just(1)
val flow: Flow = observable.toFlowable().asFlow()
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val observable: Observable = Observable.just(1)
val flow: Flow = observable.toFlowable().asFlow()
val observable2: Observable = flow.asPublisher().toObservable()
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RxJava
Subject / Relay
flatMap()
concatMap()
switchMap()
Flow
channel.asFlow()
flatMapMerge()
flatMapConcat()
switchMap()
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RxJava & Flow
map()
filter()
combineLatest()
take()
scan()
retry()
debounce()
distinctUntilChanged()
zip()
takeUntil()
reduce()
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interface MyService {
@GET(“{user}/books/favorite”)
suspend fun getFavoriteBook(@Path(“user") userId: Int): Book
}
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new
in
2.6.0
interface MyService {
@GET(“{user}/books/favorite”)
suspend fun getFavoriteBook(@Path(“user") userId: Int): Book
}
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flow {
emit(userId1)
emit(userId2)
}
interface MyService {
@GET("{user}/books/favorite")
suspend fun getFavoriteBook(@Path("user") userId: Int): Book
}
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flow {
emit(userId1)
emit(userId2)
}.someOperator { userId ->
val book = myService.getFavoriteBook(userId)
book
}
interface MyService {
@GET("{user}/books/favorite")
suspend fun getFavoriteBook(@Path("user") userId: Int): Book
}
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flow {
emit(userId1)
emit(userId2)
}.someOperator { userId ->
val book = myService.getFavoriteBook(userId)
book
}.collect { book ->
println(book)
}
interface MyService {
@GET("{user}/books/favorite")
suspend fun getFavoriteBook(@Path("user") userId: Int): Book
}
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flow {
emit(userId1)
emit(userId2)
}.map { userId ->
val book = myService.getFavoriteBook(userId)
book
}.collect { book ->
println(book)
}
interface MyService {
@GET("{user}/books/favorite")
suspend fun getFavoriteBook(@Path("user") userId: Int): Book
}
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Summary
• Flow: event stream
• Observer Pattern
• Backed by Coroutines
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