On occasion, we will wind up with a Flow of Flow objects. For example, we might get a Flow with results from a database query, and each row in those results requires another call that results in another Flow. In these cases, it can be convenient to "flatten" the flow-of-flows into a single Flow emitting each of the nested results. There are two operators for that: flattenConcat() and flattenMerge().

flattenConcat() subscribes to the first of the inner Flow objects. flattenConcat() emits each of items emitted by that inner Flow, and when that Flow completes, flattenConcat() subscribes to the next of the inner Flow objects. This continues until the outer Flow itself completes.

Here, flowRepeat() emits the same object a specified number of times, with a 10-millisecond delay between each emission. That Flow will be run on Dispatchers.Default, courtesy of flowOn(). We wrap four of those flowRepeat() calls in an outer Flow and use flattenConcat() on it. The result is that we get all 10 of the 1 items, followed by all 10 of the 2 items, etc.

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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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