问题

Sample from Kotlin Coroutine: 来自Kotlin Coroutine的示例 https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/sample.html

Doesn't emit the last element if the parent flow is finished before the time frame.：如果父流在时间窗口之前完成，则不会发出最后一个元素。

From Docs: 来自文档：

Note that the latest element is not emitted if it does not fit into the sampling window.：请注意，如果最新元素不适合抽样窗口，则不会发出。

I want an operator that acts just as the sample but emits the last value when the timeframe reaches.：我想要一个操作符，与抽样相同，但在时间窗口到达时发出最后一个值。

The last value is important in my case.：在我的情况下，最后一个值很重要。

Eg code: 例如代码：

val k = (0..100).asFlow().onEach {
    delay(200)
}

val k2 = k.sample(500)

k2.collectLatest {
    println(it)
}

A custom operator would do if none is provided by the library.：如果库中没有提供操作符，可以使用自定义操作符。

val k = (0..100).asFlow().onEach {
        delay(200)
    }

    val k2 = k.sample(500)

    k2.collectLatest {
        println(it)
    }

答案1

得分: 1

你可以尝试这个。这段代码应该是不言自明的。我没有严格测试过它！

fun <T> Flow<T>.sampleAndKeepLast(periodMillis: Long): Flow<T> {
    require(periodMillis > 0) { "Sample period should be positive" }
    return channelFlow {
        var isDone = false
        val empty = Any()
        var lastValue: Any? = empty
        onEach { lastValue = it }
            .onCompletion { isDone = true }
            .launchIn(this)
        while (!isDone) {
            delay(periodMillis)
            if (lastValue !== empty) {
                @Suppress("UNCHECKED_CAST")
                send(lastValue as T)
                lastValue = empty
            }
        }
        if (lastValue !== empty) {
            @Suppress("UNCHECKED_CAST")
            send(lastValue as T)
        }
    }
}

fun <T> Flow<T>.sampleAndKeepLast(periodMillis: Long): Flow<T> {
    require(periodMillis > 0) { "Sample period should be positive" }
    return channelFlow {
        var isDone = false
        val empty = Any()
        var lastValue: Any? = empty
        onEach { lastValue = it }
            .onCompletion { isDone = true }
            .launchIn(this)
        while (!isDone) {
            delay(periodMillis)
            if (lastValue !== empty) {
                @Suppress("UNCHECKED_CAST")
                send(lastValue as T)
                lastValue = empty
            }
        }
        if (lastValue !== empty) {
            @Suppress("UNCHECKED_CAST")
            send(lastValue as T)
        }
    }
}