How to transform an Android Task to a Kotlin Deferred?

Question

Firebase anonymous sign in returns a task (which is basically Google promise implementation):

val task:Task = FirebaseAuth.getInstance().si         


        

Answer 1

Based on this GitHub library, here's a way to transform a Task into a suspending function in the "usual" way to adapt callback based async calls to coroutines:

suspend fun  Task.await(): T = suspendCoroutine { continuation ->
    addOnCompleteListener { task ->
        if (task.isSuccessful) {
            continuation.resume(task.result)
        } else {
            continuation.resumeWithException(task.exception ?: RuntimeException("Unknown task exception"))
        }
    }
}

You can also wrap it in a Deferred of course, CompletableDeferred comes in handy here:

fun  Task.asDeferred(): Deferred {
    val deferred = CompletableDeferred()

    deferred.invokeOnCompletion {
        if (deferred.isCancelled) {
            // optional, handle coroutine cancellation however you'd like here
        }
    }

    this.addOnSuccessListener { result -> deferred.complete(result) }
    this.addOnFailureListener { exception -> deferred.completeExceptionally(exception) }

    return deferred
}