如何从Java 7调用Kotlin暂停协程函数 [英] How to call Kotlin suspending coroutine function from Java 7

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问题描述

我正在尝试从Java 7调用Kotlin函数.我正在使用协程,并且这个被调用的函数正在挂起,例如:

I'm trying to call Kotlin function from Java 7. I'm using coroutines and this called function is suspending, for example:

suspend fun suspendingFunction(): Boolean {
    return async { longRunningFunction() }.await()
}

suspend fun longRunningFunction() : Boolean {
    delay(400)
    return true
}

我在0.25.3版中使用了协程,我可以通过将Continuation<U>实例作为挂起函数的参数来模拟简单的Java回调样式,例如

I was using coroutines in version 0.25.3 and I could emulate simple Java callback style by passing Continuation<U> instance as an argument to suspending function, e.g.

CoroutinesKt.suspendingFunction(new Continuation<Boolean>() {
    @Override
    public CoroutineContext getContext() {
        return EmptyCoroutineContext.INSTANCE;
    }

    @Override
    public void resume(Boolean value) {
        doSomethingWithResult(value);
    }

    @Override
    public void resumeWithException(@NotNull Throwable throwable) {
        handleException(throwable);
    }
});

但是,在更新到完全稳定的1.0.1版本之后,我认为它不再可行.假设暂停功能的更新版本如下:

However, after updating to fully stable 1.0.1 release, I think it's no longer possible. Let's say updated version of suspending function looks like that:

suspend fun suspendingFunction(): Boolean {
    return GlobalScope.async { longRunningFunction() }.await()
}

Continuation<U>现在使用Result类,这在Java中似乎无法使用(这是内联类,因此很有意义).我试图使用协程的某些Continuation子类,但它们都是内部的或私有的.

Continuation<U> now uses Result class, which seems to be unusable from Java (which makes sense as it is inline class). I was trying to use some subclass of Continuation from coroutines but they are all internal or private.

我知道通常是建议将协程转换为CompletableFuture ,但我使用的是Android,这意味着仅Java 7.另一方面,简单的Future太笨了,因为我不想定期检查函数是否完成-我只想在函数完成时被调用.而且我真的很想避免添加新的库或许多其他的类/方法.

I know that usually it is advised to transform coroutine to CompletableFuture, but I'm on Android, which means Java 7 only. Simple Future on the other hand is too dumb as I don't want to check periodically if function is finished - I just want to be called when it is finished. And I would really like to avoid adding new libraries or many additional classes/methods.

有没有简单的方法可以直接从Java 7中调用暂停功能?

当Kotlin试图与Java互操作性很强时,我会想到会有一些简单的方法来做到这一点,但是我还没有找到它.

As Kotlin tries to be very interoperable with Java I would imagine there would be some easy way to do that, but I'm yet to find it.

推荐答案

根据您的环境,您有几种选择.

You have several options depending on your environment.

  1. 如果在项目中使用RxJava2,则模块kotlinx-coroutines-rx2具有实用程序功能,可以在协程和Rx数据类型之间来回转换.
  1. If you are using RxJava2 in the project, the module kotlinx-coroutines-rx2 has utility functions to convert back and forth between coroutines and Rx datatypes.

示例

suspend fun sayHello(): String {
    delay(1000)
    return "Hi there"
}

fun sayHelloSingle(): Single<String> = GlobalScope.rxSingle { sayHello() }

  1. 否则,您可以添加一个新的Continuation类,该类与旧类的定义匹配,并且在Java方面也很有用.
  1. Otherwise, you could add a new Continuation class that matches the definition of the old one and is also useful in the Java side.

示例(科特林一侧)

abstract class Continuation<in T> : kotlin.coroutines.Continuation<T> {
    abstract fun resume(value: T)
    abstract fun resumeWithException(exception: Throwable)
    override fun resumeWith(result: Result<T>) = result.fold(::resume, ::resumeWithException)
}   

示例(Java端)

sayHello(new Continuation<String>() {
    @Override
    public CoroutineContext getContext() {
        return EmptyCoroutineContext.INSTANCE;
    }

    @Override
    public void resume(String value) {
        doSomethingWithResult(value);
    }

    @Override
    public void resumeWithException(@NotNull Throwable throwable) {
        doSomethingWithError(throwable);
    }
});

这篇关于如何从Java 7调用Kotlin暂停协程函数的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!

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