Merge "Add optional emitFirstEvent param to setChanges()" into tm-qpr-dev (6451a04d) · Commits · e / os / android_frameworks_base

packages/SystemUI/src/com/android/systemui/util/kotlin/Flow.kt

+22 −3

Original line number	Diff line number	Diff line
		@@ -74,10 +74,19 @@ data class WithPrev<T>(val previousValue: T, val newValue: T)
		/**
		* Returns a new [Flow] that combines the [Set] changes between each emission from [this] using
		* [transform].
		*
		* If [emitFirstEvent] is `true`, then the first [Set] emitted from the upstream [Flow] will cause
		* a change event to be emitted that contains no removals, and all elements from that first [Set]
		* as additions.
		*
		* If [emitFirstEvent] is `false`, then the first emission is ignored and no changes are emitted
		* until a second [Set] has been emitted from the upstream [Flow].
		*/
		fun <T, R> Flow<Set<T>>.setChangesBy(
		transform: suspend (removed: Set<T>, added: Set<T>) -> R,
		): Flow<R> = onStart { emit(emptySet()) }.distinctUntilChanged()
		emitFirstEvent: Boolean = true,
		): Flow<R> = (if (emitFirstEvent) onStart { emit(emptySet()) } else this)
		.distinctUntilChanged()
		.pairwiseBy { old: Set<T>, new: Set<T> ->
		// If an element was present in the old set, but not the new one, then it was removed
		val removed = old - new
		@@ -86,8 +95,18 @@ fun <T, R> Flow<Set<T>>.setChangesBy(
		transform(removed, added)
		}

		/** Returns a new [Flow] that produces the [Set] changes between each emission from [this]. */
		fun <T> Flow<Set<T>>.setChanges(): Flow<SetChanges<T>> = setChangesBy(::SetChanges)
		/**
		* Returns a new [Flow] that produces the [Set] changes between each emission from [this].
		*
		* If [emitFirstEvent] is `true`, then the first [Set] emitted from the upstream [Flow] will cause
		* a change event to be emitted that contains no removals, and all elements from that first [Set]
		* as additions.
		*
		* If [emitFirstEvent] is `false`, then the first emission is ignored and no changes are emitted
		* until a second [Set] has been emitted from the upstream [Flow].
		*/
		fun <T> Flow<Set<T>>.setChanges(emitFirstEvent: Boolean = true): Flow<SetChanges<T>> =
		setChangesBy(::SetChanges, emitFirstEvent)

		/** Contains the difference in elements between two [Set]s. */
		data class SetChanges<T>(

packages/SystemUI/tests/src/com/android/systemui/util/kotlin/FlowUtilTests.kt

+11 −0

Original line number	Diff line number	Diff line
		@@ -127,6 +127,17 @@ class SetChangesFlowTest : SysuiTestCase() {
		)
		)
		}

		@Test
		fun dontEmitFirstEvent() = runBlocking {
		assertThatFlow(flowOf(setOf(1, 2), setOf(2, 3)).setChanges(emitFirstEvent = false))
		.emitsExactly(
		SetChanges(
		removed = setOf(1),
		added = setOf(3),
		)
		)
		}
		}

		private fun <T> assertThatFlow(flow: Flow<T>) = object {