When querying an Android `ContentResolver` you can optionally pass a `CancellationSignal` argument. ...

# coroutines

[Mark]

When querying an Android ContentResolver you can optionally pass a CancellationSignal argument. So I would like to call cancel() on that object when the coroutine is cancelled. Is there a way to do this without using suspendCancellableCoroutine (since I don’t need the whole resume() functionality)?

suspendCancellableCoroutine<Result> { continuation ->
    val cancellationSignal = CancellationSignal()
	continuation.invokeOnCancellation { 
    	cancellationSignal.cancel()
	}
	val result: Result = resolver.query(args, cancellationSignal)
	continuation.resume(result)
}

[octylFractal]

coroutineContext[Job]!!.invokeOnCompletion takes an argument to inform you of cancellation as well, could probably use that

[Mark]

Thanks! I wonder about tidying up once the query has finished. Can it be cleared?

[octylFractal]

yes, see https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/-job/invoke-on-completion.html

[Mark]

Ah, thanks I missed that DisposableHandle

suspend inline fun <T> usingCancellationSignal(action: (CancellationSignal) -> T): T {
    val cancellationSignal = CancellationSignal()
    val disposableHandle = coroutineContext[Job]!!.invokeOnCompletion { cause ->
        if (cause is CancellationException) {
            cancellationSignal.cancel()
        }
    }
    try {
        return action(cancellationSignal)
    } finally {
        disposableHandle.dispose()
    }
}

[Mark]

I added a check to make sure CancellationSignal.cancel() is only called when the cause is CancellationException