kotlin - 测试代码时为什么会出现错误 “Unresolved reference: launch”？

Question

我正在学习Kotlin的协程，我是https://try.kotlinlang.org/中在线运行代码的初学者

我尝试在网站上测试代码A，但是像图像A一样出现很多错误，我该如何解决？

代码A

import kotlinx.coroutines.*

fun main(args: Array<String>) {

    val job = launch {
      val child = launch {
         try {
            delay(Long.MAX_VALUE)
         } finally {
             println("Child is cancelled")
         }
      }

      yield()
      println("Cancelling child")
      child.cancel()
      child.join()
      yield()
      println("Parent is not cancelled")
    }

    job.join()

}

图片

Answer 1

尝试运行以下代码:

import kotlinx.coroutines.*
import kotlin.coroutines.CoroutineContext

fun main() = runBlocking<Unit> { //here i made change
    val job = launch {
      val child = launch {
         try {
            delay(Long.MAX_VALUE)
         } finally {
             println("Child is cancelled")
         }
      }

      yield()
      println("Cancelling child")
      child.cancel()
      child.join()
      yield()
      println("Parent is not cancelled")
    }

    job.join()

}

输出将是:)

Cancelling child
Child is cancelled
Parent is not cancelled