kotlinx-coroutines-core/kotlinx.coroutines.flow/MutableStateFlow

MutableStateFlow

interface MutableStateFlow<T> : StateFlow<T> , MutableSharedFlow<T> (source)

A mutable StateFlow that provides a setter for value. An instance of MutableStateFlow with the given initial value can be created using MutableStateFlow(value) constructor function.

See the StateFlow documentation for details on state flows.

Not stable for inheritance

The MutableStateFlow interface is not stable for inheritance in 3rd party libraries, as new methods might be added to this interface in the future, but is stable for use. Use the MutableStateFlow() constructor function to create an implementation.

Functions

compareAndSet

abstract fun compareAndSet(expect: T, update: T): Boolean

Atomically compares the current value with expect and sets it to update if it is equal to expect. The result is true if the value was set to update and false otherwise.

Properties

value

abstract override var value: T

The current value of this state flow.

Extensions

asSharedFlow

fun <T> MutableSharedFlow<T>.asSharedFlow(): SharedFlow<T>

Represents this mutable shared flow as a read-only shared flow.

asStateFlow

fun <T> MutableStateFlow<T>.asStateFlow(): StateFlow<T>

Represents this mutable state flow as a read-only state flow.

buffer

fun <T> Flow<T>.buffer(capacity: Int = BUFFERED, onBufferOverflow: BufferOverflow = BufferOverflow.SUSPEND): Flow<T>

Buffers flow emissions via channel of a specified capacity and runs collector in a separate coroutine.

cancellable

fun <T> Flow<T>.cancellable(): Flow<T>

Returns a flow which checks cancellation status on each emission and throws the corresponding cancellation cause if flow collector was cancelled. Note that flow builder and all implementations of SharedFlow are cancellable by default.

catch

fun <T> Flow<T>.catch(action: suspend FlowCollector<T>.(cause: Throwable) -> Unit): Flow<T>

Catches exceptions in the flow completion and calls a specified action with the caught exception. This operator is transparent to exceptions that occur in downstream flow and does not catch exceptions that are thrown to cancel the flow.

collect

suspend fun Flow<*>.collect()

Terminal flow operator that collects the given flow but ignores all emitted values. If any exception occurs during collect or in the provided flow, this exception is rethrown from this method.

collectIndexed

inline suspend fun <T> Flow<T>.collectIndexed(crossinline action: suspend (index: Int, value: T) -> Unit)

Terminal flow operator that collects the given flow with a provided action that takes the index of an element (zero-based) and the element. If any exception occurs during collect or in the provided flow, this exception is rethrown from this method.

collectLatest

suspend fun <T> Flow<T>.collectLatest(action: suspend (value: T) -> Unit)

Terminal flow operator that collects the given flow with a provided action. The crucial difference from collect is that when the original flow emits a new value then the action block for the previous value is cancelled.

combine

@JvmName(name = "flowCombine")

fun <T1, T2, R> Flow<T1>.combine(flow: Flow<T2>, transform: suspend (a: T1, b: T2) -> R): Flow<R>

Returns a Flow whose values are generated with transform function by combining the most recently emitted values by each flow.

combineTransform

@JvmName(name = "flowCombineTransform")

fun <T1, T2, R> Flow<T1>.combineTransform(flow: Flow<T2>, transform: suspend FlowCollector<R>.(a: T1, b: T2) -> Unit): Flow<R>

Returns a Flow whose values are generated by transform function that process the most recently emitted values by each flow.

conflate

fun <T> Flow<T>.conflate(): Flow<T>

Conflates flow emissions via conflated channel and runs collector in a separate coroutine. The effect of this is that emitter is never suspended due to a slow collector, but collector always gets the most recent value emitted.

count

suspend fun <T> Flow<T>.count(): Int

Returns the number of elements in this flow.

suspend fun <T> Flow<T>.count(predicate: suspend (T) -> Boolean): Int

Returns the number of elements matching the given predicate.

debounce

@FlowPreview

fun <T> Flow<T>.debounce(timeoutMillis: Long): Flow<T>

@FlowPreview

fun <T> Flow<T>.debounce(timeoutMillis: (T) -> Long): Flow<T>

@FlowPreview

fun <T> Flow<T>.debounce(timeout: Duration): Flow<T>

@FlowPreview

@JvmName(name = "debounceDuration")

fun <T> Flow<T>.debounce(timeout: (T) -> Duration): Flow<T>

Returns a flow that mirrors the original flow, but filters out values that are followed by the newer values within the given timeout. The latest value is always emitted.

distinctUntilChanged

fun <T> Flow<T>.distinctUntilChanged(): Flow<T>

Returns flow where all subsequent repetitions of the same value are filtered out.

fun <T> Flow<T>.distinctUntilChanged(areEquivalent: (old: T, new: T) -> Boolean): Flow<T>

Returns flow where all subsequent repetitions of the same value are filtered out, when compared with each other via the provided areEquivalent function.

distinctUntilChangedBy

fun <T, K> Flow<T>.distinctUntilChangedBy(keySelector: (T) -> K): Flow<T>

Returns flow where all subsequent repetitions of the same key are filtered out, where key is extracted with keySelector function.

drop

fun <T> Flow<T>.drop(count: Int): Flow<T>

Returns a flow that ignores first count elements. Throws IllegalArgumentException if count is negative.

dropWhile

fun <T> Flow<T>.dropWhile(predicate: suspend (T) -> Boolean): Flow<T>

Returns a flow containing all elements except first elements that satisfy the given predicate.

emitAll

suspend fun <T> FlowCollector<T>.emitAll(channel: ReceiveChannel<T>)

Emits all elements from the given channel to this flow collector and cancels (consumes) the channel afterwards. If you need to iterate over the channel without consuming it, a regular for loop should be used instead.

suspend fun <T> FlowCollector<T>.emitAll(flow: Flow<T>)

Collects all the values from the given flow and emits them to the collector. It is a shorthand for flow.collect { value -> emit(value) }.

filter

inline fun <T> Flow<T>.filter(crossinline predicate: suspend (T) -> Boolean): Flow<T>

Returns a flow containing only values of the original flow that match the given predicate.

filterIsInstance

inline fun <R> Flow<*>.filterIsInstance(): Flow<R>

Returns a flow containing only values that are instances of specified type R.

filterNot

inline fun <T> Flow<T>.filterNot(crossinline predicate: suspend (T) -> Boolean): Flow<T>

Returns a flow containing only values of the original flow that do not match the given predicate.

filterNotNull

fun <T : Any> Flow<T?>.filterNotNull(): Flow<T>

Returns a flow containing only values of the original flow that are not null.

first

suspend fun <T> Flow<T>.first(): T

The terminal operator that returns the first element emitted by the flow and then cancels flow's collection. Throws NoSuchElementException if the flow was empty.

suspend fun <T> Flow<T>.first(predicate: suspend (T) -> Boolean): T

The terminal operator that returns the first element emitted by the flow matching the given predicate and then cancels flow's collection. Throws NoSuchElementException if the flow has not contained elements matching the predicate.

firstOrNull

suspend fun <T> Flow<T>.firstOrNull(): T?

The terminal operator that returns the first element emitted by the flow and then cancels flow's collection. Returns null if the flow was empty.

suspend fun <T> Flow<T>.firstOrNull(predicate: suspend (T) -> Boolean): T?

The terminal operator that returns the first element emitted by the flow matching the given predicate and then cancels flow's collection. Returns null if the flow did not contain an element matching the predicate.

flatMapConcat

@FlowPreview

fun <T, R> Flow<T>.flatMapConcat(transform: suspend (value: T) -> Flow<R>): Flow<R>

Transforms elements emitted by the original flow by applying transform, that returns another flow, and then concatenating and flattening these flows.

flatMapLatest

@ExperimentalCoroutinesApi

inline fun <T, R> Flow<T>.flatMapLatest(crossinline transform: suspend (value: T) -> Flow<R>): Flow<R>

Returns a flow that switches to a new flow produced by transform function every time the original flow emits a value. When the original flow emits a new value, the previous flow produced by transform block is cancelled.

flatMapMerge

@FlowPreview

fun <T, R> Flow<T>.flatMapMerge(concurrency: Int = DEFAULT_CONCURRENCY, transform: suspend (value: T) -> Flow<R>): Flow<R>

Transforms elements emitted by the original flow by applying transform, that returns another flow, and then merging and flattening these flows.

flattenConcat

@FlowPreview

fun <T> Flow<Flow<T>>.flattenConcat(): Flow<T>

Flattens the given flow of flows into a single flow in a sequential manner, without interleaving nested flows.

flattenMerge

@FlowPreview

fun <T> Flow<Flow<T>>.flattenMerge(concurrency: Int = DEFAULT_CONCURRENCY): Flow<T>

Flattens the given flow of flows into a single flow with a concurrency limit on the number of concurrently collected flows.

flowOn

fun <T> Flow<T>.flowOn(context: CoroutineContext): Flow<T>

Changes the context where this flow is executed to the given context. This operator is composable and affects only preceding operators that do not have its own context. This operator is context preserving: contextdoes not leak into the downstream flow.

fold

inline suspend fun <T, R> Flow<T>.fold(initial: R, crossinline operation: suspend (acc: R, value: T) -> R): R

Accumulates value starting with initial value and applying operation current accumulator value and each element

getAndUpdate

inline fun <T> MutableStateFlow<T>.getAndUpdate(function: (T) -> T): T

Updates the MutableStateFlow.value atomically using the specified function of its value, and returns its prior value.

last

suspend fun <T> Flow<T>.last(): T

The terminal operator that returns the last element emitted by the flow.

lastOrNull

suspend fun <T> Flow<T>.lastOrNull(): T?

The terminal operator that returns the last element emitted by the flow or null if the flow was empty.

launchIn

fun <T> Flow<T>.launchIn(scope: CoroutineScope): Job

Terminal flow operator that launches the collection of the given flow in the scope. It is a shorthand for scope.launch { flow.collect() }.

map

inline fun <T, R> Flow<T>.map(crossinline transform: suspend (value: T) -> R): Flow<R>

Returns a flow containing the results of applying the given transform function to each value of the original flow.

mapLatest

@ExperimentalCoroutinesApi

fun <T, R> Flow<T>.mapLatest(transform: suspend (value: T) -> R): Flow<R>

Returns a flow that emits elements from the original flow transformed by transform function. When the original flow emits a new value, computation of the transform block for previous value is cancelled.

mapNotNull

inline fun <T, R : Any> Flow<T>.mapNotNull(crossinline transform: suspend (value: T) -> R?): Flow<R>

Returns a flow that contains only non-null results of applying the given transform function to each value of the original flow.

onCompletion

fun <T> Flow<T>.onCompletion(action: suspend FlowCollector<T>.(cause: Throwable?) -> Unit): Flow<T>

Returns a flow that invokes the given actionafter the flow is completed or cancelled, passing the cancellation exception or failure as cause parameter of action.

onEach

fun <T> Flow<T>.onEach(action: suspend (T) -> Unit): Flow<T>

Returns a flow that invokes the given actionbefore each value of the upstream flow is emitted downstream.

onEmpty

fun <T> Flow<T>.onEmpty(action: suspend FlowCollector<T>.() -> Unit): Flow<T>

Invokes the given action when this flow completes without emitting any elements. The receiver of the action is FlowCollector, so onEmpty can emit additional elements. For example:

onStart

fun <T> Flow<T>.onStart(action: suspend FlowCollector<T>.() -> Unit): Flow<T>

Returns a flow that invokes the given actionbefore this flow starts to be collected.

onSubscription

fun <T> SharedFlow<T>.onSubscription(action: suspend FlowCollector<T>.() -> Unit): SharedFlow<T>

Returns a flow that invokes the given actionafter this shared flow starts to be collected (after the subscription is registered).

produceIn

@FlowPreview

fun <T> Flow<T>.produceIn(scope: CoroutineScope): ReceiveChannel<T>

Creates a produce coroutine that collects the given flow.

reduce

suspend fun <S, T : S> Flow<T>.reduce(operation: suspend (accumulator: S, value: T) -> S): S

Accumulates value starting with the first element and applying operation to current accumulator value and each element. Throws NoSuchElementException if flow was empty.

retry

fun <T> Flow<T>.retry(retries: Long = Long.MAX_VALUE, predicate: suspend (cause: Throwable) -> Boolean = { true }): Flow<T>

Retries collection of the given flow up to retries times when an exception that matches the given predicate occurs in the upstream flow. This operator is transparent to exceptions that occur in downstream flow and does not retry on exceptions that are thrown to cancel the flow.

retryWhen

fun <T> Flow<T>.retryWhen(predicate: suspend FlowCollector<T>.(cause: Throwable, attempt: Long) -> Boolean): Flow<T>

Retries collection of the given flow when an exception occurs in the upstream flow and the predicate returns true. The predicate also receives an attempt number as parameter, starting from zero on the initial call. This operator is transparent to exceptions that occur in downstream flow and does not retry on exceptions that are thrown to cancel the flow.

runningFold

fun <T, R> Flow<T>.runningFold(initial: R, operation: suspend (accumulator: R, value: T) -> R): Flow<R>

Folds the given flow with operation, emitting every intermediate result, including initial value. Note that initial value should be immutable (or should not be mutated) as it is shared between different collectors. For example:

runningReduce

fun <T> Flow<T>.runningReduce(operation: suspend (accumulator: T, value: T) -> T): Flow<T>

Reduces the given flow with operation, emitting every intermediate result, including initial value. The first element is taken as initial value for operation accumulator. This operator has a sibling with initial value -- scan.

sample

@FlowPreview

fun <T> Flow<T>.sample(periodMillis: Long): Flow<T>

@FlowPreview

fun <T> Flow<T>.sample(period: Duration): Flow<T>

Returns a flow that emits only the latest value emitted by the original flow during the given sampling period.

scan

fun <T, R> Flow<T>.scan(initial: R, operation: suspend (accumulator: R, value: T) -> R): Flow<R>

shareIn

fun <T> Flow<T>.shareIn( scope: CoroutineScope, started: SharingStarted, replay: Int = 0): SharedFlow<T>

Converts a coldFlow into a hotSharedFlow that is started in the given coroutine scope, sharing emissions from a single running instance of the upstream flow with multiple downstream subscribers, and replaying a specified number of replay values to new subscribers. See the SharedFlow documentation for the general concepts of shared flows.

single

suspend fun <T> Flow<T>.single(): T

The terminal operator that awaits for one and only one value to be emitted. Throws NoSuchElementException for empty flow and IllegalStateException for flow that contains more than one element.

singleOrNull

suspend fun <T> Flow<T>.singleOrNull(): T?

The terminal operator that awaits for one and only one value to be emitted. Returns the single value or null, if the flow was empty or emitted more than one value.

stateIn

fun <T> Flow<T>.stateIn( scope: CoroutineScope, started: SharingStarted, initialValue: T): StateFlow<T>

Converts a coldFlow into a hotStateFlow that is started in the given coroutine scope, sharing the most recently emitted value from a single running instance of the upstream flow with multiple downstream subscribers. See the StateFlow documentation for the general concepts of state flows.

suspend fun <T> Flow<T>.stateIn(scope: CoroutineScope): StateFlow<T>

Starts the upstream flow in a given scope, suspends until the first value is emitted, and returns a hotStateFlow of future emissions, sharing the most recently emitted value from this running instance of the upstream flow with multiple downstream subscribers. See the StateFlow documentation for the general concepts of state flows.

take

fun <T> Flow<T>.take(count: Int): Flow<T>

Returns a flow that contains first count elements. When count elements are consumed, the original flow is cancelled. Throws IllegalArgumentException if count is not positive.

takeWhile

fun <T> Flow<T>.takeWhile(predicate: suspend (T) -> Boolean): Flow<T>

Returns a flow that contains first elements satisfying the given predicate.

toCollection

suspend fun <T, C : MutableCollection<in T>> Flow<T>.toCollection(destination: C): C

Collects given flow into a destination

toList

suspend fun <T> Flow<T>.toList(destination: MutableList<T> = ArrayList()): List<T>

Collects given flow into a destination

toSet

suspend fun <T> Flow<T>.toSet(destination: MutableSet<T> = LinkedHashSet()): Set<T>

Collects given flow into a destination

transform

inline fun <T, R> Flow<T>.transform(crossinline transform: suspend FlowCollector<R>.(value: T) -> Unit): Flow<R>

Applies transform function to each value of the given flow.

transformLatest

@ExperimentalCoroutinesApi

fun <T, R> Flow<T>.transformLatest(transform: suspend FlowCollector<R>.(value: T) -> Unit): Flow<R>

Returns a flow that produces element by transform function every time the original flow emits a value. When the original flow emits a new value, the previous transform block is cancelled, thus the name transformLatest.

transformWhile

fun <T, R> Flow<T>.transformWhile(transform: suspend FlowCollector<R>.(value: T) -> Boolean): Flow<R>

Applies transform function to each value of the given flow while this function returns true.

update

inline fun <T> MutableStateFlow<T>.update(function: (T) -> T)

Updates the MutableStateFlow.value atomically using the specified function of its value.

updateAndGet

inline fun <T> MutableStateFlow<T>.updateAndGet(function: (T) -> T): T

Updates the MutableStateFlow.value atomically using the specified function of its value, and returns the new value.

withIndex

fun <T> Flow<T>.withIndex(): Flow<IndexedValue<T>>

Returns a flow that wraps each element into IndexedValue, containing value and its index (starting from zero).

zip

fun <T1, T2, R> Flow<T1>.zip(other: Flow<T2>, transform: suspend (T1, T2) -> R): Flow<R>

Zips values from the current flow (this) with other flow using provided transform function applied to each pair of values. The resulting flow completes as soon as one of the flows completes and cancel is called on the remaining flow.