I’m new to coroutines and struggling to get my head around the conceptuals while trying to implement...

# coroutines

[Andrew Ebling]

I’m new to coroutines and struggling to get my head around the conceptuals while trying to implement a debounce:

override fun onOptionsItemSelected(item: MenuItem): Boolean {
    return when(item.itemId) {
        R.id.refresh -> {
            flow {
                callbacks?.refreshAllTheThings()
            }.debounce(5000)
            return true
        }
        else -> {
            return super.onOptionsItemSelected(item)
        }
    }
}

...however I get the following compilation error: Not enough information to infer type variable T

I’ve gone and looked at the implementation of debounce() but the examples in the comments suggest what I have above should be sufficient.

Why does flow need type information if I just want to execute one line of code, at most, every 5 seconds?

[wasyl]

Flow is a flow of values that you need to collect somehow. In your example the error is just a compiler error because you don’t emit anything from the flow you create: if you just do flow<Unit> { } it would be enough to compile

[wasyl]

However, it still wouldn’t work as you expect, because creating a flow doesn’t do anything by itself without collecting it

[wasyl]

Besides, if you want debounce, you need to have just one flow for multiple clicks. Here you’d be creating a separate flow for every click anyway. I’m not sure how to best implement this with a callback like this though, you’d probably need a channel to which you post click events, and have a debounce on that channel

[wasyl]

Something like:

val clicksChannel = BroadcastChannel<Unit>(1)

fun onOptionsItemSelected() {
  clicksChannel.offer(Unit) 
}

onCreate() {
  lifecycleScope.launchWhenCreated {
    clicksChannel
      .asFlow()
      .debounce(5000)
      .collect { refreshAllThings() }
  }
}

[Andrew Ebling]

great - many thanks - getting close, but I now realise debounce is not the behaviour I’m looking for - more like throttle but seems coroutines doesn’t use this out of the box?

[Andrew Ebling]

debounce is waiting until the timeout before sending the first event

[wasyl]

I’m not sure throttle exists https://github.com/Kotlin/kotlinx.coroutines/issues/1446

[Andrew Ebling]

lol - just reading through the comments on that exact issue :smile

[wasyl]

Maybe sample would help? Not sure

[Andrew Ebling]

I think that’s done the trick - many thanks for your help! 👍

[Andrew Ebling]

Actually - I’ve learned a tonne with you guidance this morning - a whole load of conceptual stuff has fallen into place. I’m just one of those people who learns far more effectively through seeing working code than reading it all explained in-theory.

[Andrew Ebling]

Thanks again for taking time out of your day

[wasyl]

Sure, happy to help 🙂