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An event inside a Compose State or MutableState which should only be handled once
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| import androidx.compose.runtime.MutableState | |
| import androidx.compose.runtime.State | |
| import androidx.compose.runtime.saveable.Saver | |
| import androidx.compose.runtime.saveable.listSaver | |
| import kotlinx.coroutines.sync.Mutex | |
| import kotlinx.coroutines.sync.withLock | |
| /** | |
| * An event inside a [State] or [MutableState] which should only be handled once, even after | |
| * recomposition. The [consume] function ensures this. | |
| * | |
| * Note that each instance of [StateEvent] is considered unique and the encapsulated [value] is | |
| * *NOT* used for structural equality. This means that two instances of the same value are | |
| * structurally and referentially unequal. | |
| * | |
| * The class exposes the [value] property. However use the [consume] function to ensure singular | |
| * reads! | |
| * | |
| * @see create | |
| * @see none | |
| * @see of | |
| * @see saver | |
| */ | |
| class StateEvent<T> private constructor( | |
| val value: T?, | |
| ) { | |
| private var consumed = false | |
| private val mutex = Mutex() | |
| enum class ConsumeResult { | |
| Consumed, Skipped | |
| } | |
| /** | |
| * Returns `true` when the event was not yet consumed and [onConsume] was called, else `false`. | |
| * | |
| * [onConsume] must return a [ConsumeResult] to indicate whether the event was consumed or | |
| * skipped. | |
| */ | |
| suspend fun consume(onConsume: suspend (T) -> ConsumeResult): Boolean = mutex.withLock { | |
| if (value == null || consumed) return@withLock false | |
| consumed = onConsume(value) == ConsumeResult.Consumed | |
| return@withLock true | |
| } | |
| override fun toString(): String = if (value == null) { | |
| "StateEvent(None)" | |
| } else { | |
| "StateEvent(event=$value, consumed=$consumed)" | |
| } | |
| companion object { | |
| fun <T : Any> create(event: T) = StateEvent(event) | |
| fun <T> none() = StateEvent<T>(null) | |
| fun <T : Any> of(event: T?): StateEvent<T> = if (event == null) { | |
| none() | |
| } else { | |
| create(event) | |
| } | |
| @Suppress("UNCHECKED_CAST") | |
| fun <T> saver(): Saver<StateEvent<T>, *> = listSaver( | |
| save = { | |
| listOf( | |
| it.value, | |
| it.consumed, | |
| ) | |
| }, | |
| restore = { | |
| StateEvent(it[0] as T).apply { | |
| consumed = it[1] as Boolean | |
| } | |
| }, | |
| ) | |
| } | |
| } |
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