定期发出最后一个值的流，当一个新值到达时

Question

我想创建一个 Kotlin 协程 Flow，它在何时发出值

1. 它们会改变，并且
2. 自上次更改或上次发出后每隔 x 持续时间定期发出最后一个可用值。

Answer 1

这似乎可行——每次新值到达时，transformLatest 都会取消任何以前的 lambdas 并启动一个新值。所以这种方法会发出，然后继续周期性地发出，直到有新值到达。

flow.transformLatest { value ->
  while(currentCoroutineContext().isActive) {
    emit(value)
    delay(x)
  }
}

Answer 2

您可以创建一个定期发射的Flow，然后使用combine。每次合并这些值时，您实际上只是传递了您感兴趣的原始 Flow 的当前值。

    // This is the main flow you are interested in. This uses
    // a Flow builder just as a simple example but this could
    // be any kind of Flow, like a (Mutable)StateFlow.
    val emitter = flow {
        emit("Your data")
        // ...
    }
    // This just serves as a timer.
    val timer = flow {
        while (currentCoroutineContext().isActive) {
            emit(Unit)
            delay(500)
        }
    }
    // This will emit whenever either of the Flows emits and 
    // continues to do so until "emitter" stops emitting.
    combine(
        emitter,
        timer
    ) {  value, ticker ->
        // Always just return the value of your
        // main Flow.
        value
    }