问题
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
}
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);
}
});
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>
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.
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.
Is there any simple way to call suspending function directly from Java 7?
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.
回答1:
You have several options depending on your environment.
- If you are using
RxJava2
in the project, the modulekotlinx-coroutines-rx2
has utility functions to convert back and forth between coroutines and Rx datatypes.
Example
suspend fun sayHello(): String {
delay(1000)
return "Hi there"
}
fun sayHelloSingle(): Single<String> = GlobalScope.rxSingle { sayHello() }
- Otherwise, you could add a new
Continuation
class that matches the definition of the old one and is also useful in the Java side.
Example (Kotlin side)
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)
}
Example (Java side)
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);
}
});
来源:https://stackoverflow.com/questions/54022921/how-to-call-kotlin-suspending-coroutine-function-from-java-7