android - 暂停协程功能，直到收到结果，然后继续

Question

我正在慢慢学习kotlin-coroutines，希望我想从一个简单的情况开始，即我遍历列表，每次调用API调用，等待响应，进行处理，然后在每次迭代中重复该过程。

viewModelScope.launch {
     list.forEach { item ->
          Log.d("TESTING", "forEach iteration before calling test(): ${item.id}")

          test()

          Log.d("TESTING", "forEach iteration after calling test(): ${item.id}")
     }
}

suspend fun test(item.id: String) = coroutineScope {
    Log.d("TESTING", "suspend test before receiving response: ${item.id}")

    val apiRepsonse = async {
        repository.doingApiCall() {
            Log.d("TESTING", "response: ${item.id}")
        }
    }.await()

    Log.d("TESTING", "suspend test after receiving response: ${item.id}")
}

因此，如果我们想象， list包含: { 10, 15, 25, 35 }(id)

我想以 logcat接收以下内容:

Log.d("TESTING", "forEach iteration before calling test(): 10")
Log.d("TESTING", "suspend test before receiving response: 10")
Log.d("TESTING", "response: 10")
Log.d("TESTING", "suspend test after receiving response: 10")
Log.d("TESTING", "forEach iteration after calling test(): 10")
___________________
Log.d("TESTING", "forEach iteration before calling test(): 15")
Log.d("TESTING", "suspend test before receiving response: 15")
Log.d("TESTING", "response: 15")
Log.d("TESTING", "suspend test after receiving response: 15")
Log.d("TESTING", "forEach iteration after calling test(): 15")
...

但是，现在我得到这样的东西:

Log.d("TESTING", "forEach iteration before calling test(): 10")
Log.d("TESTING", "suspend test before receiving response: 10")
Log.d("TESTING", "suspend test after receiving response: 10")
Log.d("TESTING", "forEach iteration after calling test(): 10")
Log.d("TESTING", "forEach iteration before calling test(): 15")
Log.d("TESTING", "suspend test before receiving response: 15")
Log.d("TESTING", "suspend test after receiving response: 15")
Log.d("TESTING", "forEach iteration after calling test(): 15")

Log.d("TESTING", "response: 10")
Log.d("TESTING", "response: 15")

...

基本上，for-each循环移动并且不等待API异步响应。我以为 .await()是用于此场景的，但我可能在这里遗漏了一些东西，因为它显然不像我想象的那样起作用。

Answer 1

更改

val apiRepsonse = async {
        repository.doingApiCall() {
            Log.d("TESTING", "response: ${item.id}")
        }
    }.await()

至

val apiRepsonse = async {
        Log.d("TESTING", "Start work in another 'thread'.")
        repository.doingApiCall() {
            Log.d("TESTING", "Finish work in another 'thread'.")
        }
    }.await()
Log.d("TESTING", "response: ${apiRepsonse.id}")

这样一来，您等待交付的值(value)就得到了实际使用。

我认为这将消除您的LogCat困惑。

我本人试图解决您的问题，我已将其编写为可以理解的测试:

class TestFoo {

    @Test
    fun foo() {
        val job = GlobalScope.launch {
            listOf("10", "15").forEach { item ->
                println("TESTING forEach iteration before calling test(): ${item}")

                test(item)

                println("TESTING forEach iteration after calling test(): ${item}")
            }
        }
        while(job.isActive) {
            // wait
        }
    }

    private suspend fun test(item: String) = coroutineScope {
        println("TESTING suspend test before receiving response: ${item}")

        val apiRepsonse = async {
            delay(1000)
            println("TESTING response: ${item}")
            "Hello"
        }.await()

        println("TESTING suspend test after receiving response: ${item}")
    }

}

这是“LogCat”:



您是否因为 repository.doingApiCall()内部发生了一些线程而获得了不同的日志？