Merge "Add optional emitFirstEvent param to setChanges()" into tm-qpr-dev am: 6451a04d78 am: 272a3cf8f4
Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/19776116
Change-Id: Iaa2b6a93fe70ada662ef4d2137b6a303cc910c7a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>
diff --git a/packages/SystemUI/src/com/android/systemui/util/kotlin/Flow.kt b/packages/SystemUI/src/com/android/systemui/util/kotlin/Flow.kt
index 7baebf4..729fdfe 100644
--- a/packages/SystemUI/src/com/android/systemui/util/kotlin/Flow.kt
+++ b/packages/SystemUI/src/com/android/systemui/util/kotlin/Flow.kt
@@ -74,10 +74,19 @@
/**
* 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 @@
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>(
diff --git a/packages/SystemUI/tests/src/com/android/systemui/util/kotlin/FlowUtilTests.kt b/packages/SystemUI/tests/src/com/android/systemui/util/kotlin/FlowUtilTests.kt
index 092e82c..460b71f 100644
--- a/packages/SystemUI/tests/src/com/android/systemui/util/kotlin/FlowUtilTests.kt
+++ b/packages/SystemUI/tests/src/com/android/systemui/util/kotlin/FlowUtilTests.kt
@@ -127,6 +127,17 @@
)
)
}
+
+ @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 {