I want to periodically read the value of the stepc...

# android

[kotlinforandroid]

I want to periodically read the value of the stepcounter sensor using a androidx.work.Worker . However, reading the value requires me to register a callback. How do I make my worker wait for the callback to return once without using a busy-loop? Is there a builtin way? JobService has a dedicated finishJob method that one could call from the callback. androidx.work seems to not have this

class MyWorker(sm: SensorManager, sensor: Sensor, context: Context, params: WorkerParameter): Worker(context, params) {
    private flag: Boolean = false

    override fun doWork(): Result {
        sm.registerListener(object : SensorEventListener {
            override fun onSensorEvent(e: SensorEvent) {
                flag = true
                // use value...
            }
        }, sensor, TIMEFRAME_FASTEST)
        
        while (!flag) {  }
        return Result.success()
    }
}

[Adam Powell]

If you use a CoroutineWorker you can use suspending to do it

[kotlinforandroid]

@Adam Powell I don't see how that can be useful given that the `registerListener`` method isn't suspend and I cannot wait for a result in a CoroutineContext. Could you further elaborate on your suggestion? Maybe showing a code snippet on how you would use CoroutineWorker .

[Casey Brooks]

Here’s the documentation for `CoroutineWorker`: https://developer.android.com/topic/libraries/architecture/workmanager/advanced/coroutineworker

And suspendCancellableCoroutine is the bridge between the callback-based registerListener and coroutines

So you’d end up with a doWork() function like this:

override suspend fun doWork(): Result {
    return suspendCancellableCoroutine { continuation ->
        sm.registerListener(object : SensorEventListener {
            override fun onSensorEvent(e: SensorEvent) {
                // use value...
                continuation.resume(Result.success())
            }
        }, sensor, TIMEFRAME_FASTEST)
    }
}

[kotlinforandroid]

I wasnt aware of suspendCancellableCoroutine, thank you!

[Adam Powell]

or build it using a callbackFlow {} or similar. I'd assume that the above snippet verbatim with suspendCancellableCoroutine would still leave the listener registered; whatever solution you go with should account for cleaning that up

[gildor]

Yes, example above doesn’t handle cancellation and leaks and also will throw exception on second sensor event (because it already returned)

It’s better to use Flow anyway to wrap callbacks which could be called multiple times and then just do myFlow.first() if you wait for only 1 event