Call Kotlin suspend function in Java class

问题

Assume we have the following suspend function:

suspend fun doSomething(): List<MyClass> { ... }

If I want to call this function in one of my existing Java classes (which I'm not able to convert to Kotlin for now) and get its return value I have to provide a Continuation<? super List<MyClass>> as its parameter (Obviously).

My question is, How can I implement one. Specially its getContext getter.

回答1:

First, add org.jetbrains.kotlinx:kotlinx-coroutines-jdk8 module to your dependencies. In your Kotlin file define the following async function that corresponds to Java style of writing async APIs:

fun doSomethingAsync(): CompletableFuture<List<MyClass>> =
    GlobalScope.future { doSomething() }

Now use doSomethingAsync from Java in the same way as you are using other asynchronous APIs in the Java world.

回答2:

For coroutines 1.3.0 use this:

BuildersKt.launch(GlobalScope.INSTANCE,
                Dispatchers.getMain(),//context to be ran on
                CoroutineStart.DEFAULT,
                (coroutineScope, continuation) -> suspendFunction(arguments)
        );

For java < 8:

BuildersKt.launch(
        GlobalScope.INSTANCE,
        Dispatchers.getMain(),//context to be ran on
        CoroutineStart.DEFAULT,
        new Function2<CoroutineScope, Continuation<? super Unit>, Unit/*or your return type here*/>() {
            @Override
            public Unit/*or your return type here*/ invoke(CoroutineScope coroutineScope, Continuation<? super Unit> continuation) {
                //do what you want
                return Unit.INSTANCE; //or something with the defined type
            }
        }
);

My gradle file:

implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.3.50"
implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.0"
implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.0"

Kotlin uses static classes for extension functions, launch is an extension function, so it is defined in BuildersKt. The first parameter is the target of the extension function, the rest are the parameters from the extension functions.

来源：https://stackoverflow.com/questions/52869672/call-kotlin-suspend-function-in-java-class

标签

java

kotlin

kotlin-coroutines