StateFlow and MutableStateFlow are also relatively new additions to coroutines. A StateFlow is a bit like a Flow edition of a ConflatedBroadcastChannel:

  • It can be observed by multiple parties, like a SharedFlow

  • Objects placed into the flow are conflated

The holder of a StateFlow can not only use Flow-like constructs to observe the flow (e.g., collect()) but also can use a value property to get the most-recent object placed onto the StateFlow. Also, once an observer starts observing, it immediately receives the most-recent object, in addition to future ones while it is observing.

The typical way to set up a StateFlow is to use a MutableStateFlow. The constructor-style factory function takes the initial state as a parameter, and you can use the value property to change that state as needed.

Here, we emit the names of the 50 US states onto a MutableStateFlow. With the 200 millisecond delay, the consumer can keep up, and you should see all 50 in the output. But, if you edit this sample and comment out the delay() call, you will find that most of the states get conflated, so the output shows only a subset, often just the first and last.

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A Conflated Channel A Fixed-Buffer Channel A Parallel Coroutine Sample A Sequential Coroutine Sample A Simple Channel A Simple Coroutine Sample A Simple Flow A Simple SharedFlow A Simple StateFlow A Zero-Buffer Channel async() BroadcastChannel cancelAndJoin() Canceling a Job Canceling a Parent Cancels Its Children Canceling and Cooperation catch() Channel and receive() Channels and Fan-out combine() Operator Contexts and Jobs Cooperation by Checking isActive Cooperation by Yielding debounce() Operator distinctUntilChanged() Operator distinctUntilChangedBy() Operator drop() Operator dropWhile() Operator filter() Operator filterIsInstance() Operator filterNot() Operator filterNotNull() Operator first() and Flow flattenConcat() Operator flattenMerge() Operator Flow Actions Flow onStart() flowOf() flowOn() Flows and Exceptions fold() Operator Hot Channels Via offer() invokeOnCompletion() Jobs and Parents Jobs Cancel When They Crash join() Lazy Coroutines map() Operator mapLatest() Operator mapNotNull() Operator Massively Parallel Coroutines MutableSharedFlow Replay Option Non-Cancellable Coroutines Parent Jobs Cancel When a Child Crashes promise() retry() retryWhen() runBlocking() sample() Operator scan() Operator single() and singleOrNull() Starting Lazy Coroutines StateFlow and Content Equality suspend Functions and Flows Suspending main() take() Operator takeWhile() Operator The Channel() Function TimeoutCancellationException Timeouts toList() and toSet() toList() for Channel withIndex() Operator withTimeoutOrNull() zip() Operator
A Simple Flow A Simple SharedFlow A Simple StateFlow catch() combine() Operator debounce() Operator distinctUntilChanged() Operator distinctUntilChangedBy() Operator drop() Operator dropWhile() Operator filter() Operator filterIsInstance() Operator filterNot() Operator filterNotNull() Operator first() and Flow flattenConcat() Operator flattenMerge() Operator Flow Actions Flow onStart() flowOf() flowOn() Flows and Exceptions fold() Operator map() Operator mapLatest() Operator mapNotNull() Operator MutableSharedFlow Replay Option retry() retryWhen() sample() Operator scan() Operator single() and singleOrNull() StateFlow and Content Equality suspend Functions and Flows take() Operator takeWhile() Operator toList() and toSet() withIndex() Operator zip() Operator
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