带有返回值的 Kotlin 协程

Question

我想创建一个有返回值的协程方法。

例如）

fun funA() = async(CommonPool) {
    return 1
}

fun funB() = async(CommonPool) {
    return 2
}

fun sum() {
    launch {
        val total = funA().await() + funB().await()
    }
}

如果我想用 sum 方法返回总和，我应该怎么做？

喜欢，

fun sum(): Int {
    launch {
        val total = funA().await() + funB().await()
    }   

    return total
}

Answer 1

要准确返回Int，您需要离开协程世界，这就是runBlocking 的用途：

fun sum(): Int = runBlocking {
    funA().await() + funB().await()
}

请参阅协程指南中的Bridging blocking and non-blocking worlds，如果您想在协程中使用sum，请参阅Composing suspending functions。inside 协程。

Answer 2

回答这个问题可能为时已晚，但希望有人会发现它很有用。下面的代码 sn-p 计算 3 个值 A + B + C 的总和。每个值在其自己的后台线程中并行独立计算，然后将所有中间结果合并为一个最终结果并返回到主线程显示在一个屏幕。

所以计算最终值需要 5 秒（不是 10 秒 = 2 + 3 + 5），结果显然是 6 并且它是非阻塞的，主线程可以处理其他事件而 sum() 执行不是完成。

suspend fun sum(scheduler: ThreadPoolExecutor): Int = coroutineScope {

    withContext(scheduler.asCoroutineDispatcher()) {
        val a = async { funA() }
        val b = async { funB() }
        val c = async { funC() }

        a.await() + b.await() + c.await()
    }
}

fun funA(): Int {
    Thread.sleep(2000L)
    return 1
}

fun funB(): Int {
    Thread.sleep(3000L)
    return 2
}

fun funC(): Int {
    Thread.sleep(5000L)
    return 3
}

class MainActivity : AppCompatActivity(), View.OnClickListener {
    private val tripletsPool = ThreadPoolExecutor(3, 3, 5L, TimeUnit.SECONDS, LinkedBlockingQueue())

   ...

    override fun onClick(view: View?) {
        if (view == null) {
            return
        }

        when (view.id) {
            R.id.calculate -> {
                GlobalScope.launch(Dispatchers.Main, CoroutineStart.DEFAULT) {
                    progressBar.visibility = View.VISIBLE
                    result.setText("${sum(tripletsPool)}")
                    progressBar.visibility = View.GONE
                }
            }
        }
    }
}

Answer 3

添加另一种实现方式。

fun sum(): Int {
    var sum: Int = 0
    runBlocking {
        val jobA = async { funA() }
        val jobB = async { funB() }
        runBlocking{
           sum = jobA.await() + jobB.await()
        }
    }
    return sum
}

suspend fun funA(): Int {
    return 1
}

suspend fun funB(): Int {
    return 2
}

Answer 4

我编辑你的工作，我将 funA 和 funB 更改为挂起函数，我为 sum 运算符创建了一个函数，我调用了 main 函数，这个例子：

suspend fun funA(): Int{
    return 1
}

suspend fun funB(): Int {
    return 2
}
fun sum() = runBlocking{
    val resultSum = async { funA.await() + funB.await() }
    return resultSum
}

fun main() = runBlocking{
    val result = async { sum() }
    println("Your result: ${result.await()}")
}

希望对你有帮助

Answer 5

这是在不使用runBlocking 的情况下并行运行funA() 和funB() 的另一种方法。

fun funA() = CoroutineScope(Dispatchers.IO).async {
    delay(3000)
    return@async 1
}

fun funB() = CoroutineScope(Dispatchers.IO).async {
    delay(3000)
    return@async 2
}

fun sum() = CoroutineScope(Dispatchers.IO).async {
    val a = funA()
    val b = funB()
    return@async a.await() + b.await()
}

如果你想在不阻塞主线程的情况下运行sum()，

CoroutineScope(Dispatchers.IO).launch {
    measureTimeMillis {
        Log.d("TAG", "sum=${sum().await()}")
    }.also {
        Log.d("TAG", "Completed in $it ms")
    }
}

Answer 6

这是我的做法，在尝试从我的 Room 数据库中删除电话号码时返回一个布尔值。您可以使用相同的模式来完成您想要完成的任务。在我的视图模型中：

private var parentJob = Job()
private val coroutineContext: CoroutineContext get() = parentJob + Dispatchers.Main
private val scope = CoroutineScope(coroutineContext)

suspend fun removePhoneNumber(emailSets: EmailSets, personDetails: PersonDetails) : Boolean  {
    var successReturn = false
    scope.async(Dispatchers.IO) {
        val success = async {removePhoneNumbersAsync(emailSets,personDetails)}
        successReturn = success.await()

    }
    return successReturn
}

fun removePhoneNumbersAsync(emailSets: EmailSets, personDetails : PersonDetails):Boolean {
    var success = false
    try {
        val emailAddressContact = EmailAddressContact(emailSets.databaseId, personDetails.id, personDetails.active)
        repository.deleteEmailAddressContact(emailAddressContact)
        val contact = Contact(personDetails.id, personDetails.personName, personDetails.personPhoneNumber, 0)  
        repository.deleteContact(contact)
        success = true
    } catch (exception: Exception) {
        Timber.e(exception)
    }
    return success
}

在我的活动中：

runBlocking {
    if (v.tag != null) {
            val personDetails = v.tag as PersonDetails
            val success  = viewModel.removePhoneNumber(emailSets,personDetails)
            if (success) {
                val parentView = v.parent as View
                (parentView as? TableRow)?.visibility = View.GONE
                val parentViewTable = parentView.parent as ViewGroup
                (parentViewTable as? TableLayout)
                parentViewTable.removeView(parentView)
            }
     }

}