我正在尝试使用流来编写秒表。

import kotlinx.coroutines.delay
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.map
import kotlinx.coroutines.launch
import kotlinx.coroutines.runBlocking

fun main(): Unit = runBlocking{
    val startTime = System.currentTimeMillis()
    val elapsedTime = MutableStateFlow(0L)
    // start stopwatch
    launch {
        while(true){
            elapsedTime.value = System.currentTimeMillis() - startTime
            delay(100)
        }
    }

    // update ui
    launch {
        elapsedTime.map{
            it/1000
        }.collect{
            println("$it seconds")
        }
    }
}

0 seconds
0 seconds
0 seconds
0 seconds
0 seconds
0 seconds
0 seconds
0 seconds
0 seconds
0 seconds
1 seconds
1 seconds
1 seconds

问题是中间流不会像下面的代码一样跟踪值是否发生了变化：

import kotlinx.coroutines.delay
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.map
import kotlinx.coroutines.launch
import kotlinx.coroutines.runBlocking

fun main(): Unit = runBlocking{
    val startTime = System.currentTimeMillis()
    val elapsedTime = MutableStateFlow(0L)
    // start stopwatch
    launch {
        while(true){
            elapsedTime.value = (System.currentTimeMillis() - startTime)/1000
            delay(5)
        }
    }

    // update ui
    launch {
        elapsedTime.collect{
            println("$it seconds")
        }
    }
}

0 seconds
1 seconds
2 seconds
3 seconds

我希望有一个单一的根流elapsedTime.value = System.currentTimeMillis() - startTime，从中我可以有多个观察者，使用.map{it/a}具有不同的精度水平。有没有一个干净的方法来实现这一点？