What is the prefered way of sending one time event...

# mvikotlin

[Nikola Milovic]

What is the prefered way of sending one time events to the UI from the stores? Example, we have a success and want to notify the user, I'd emit a Label and I'd be able to catch it in the Component, but how can I send it from Component -> UI?

[rsktash]

I think you need to expose store.labels field

[Nikola Milovic]

Got an example perhaps?

[Arkadii Ivanov]

Hello. How UI is implemented? Android views, Compose, or something else?

[Nikola Milovic]

@Arkadii Ivanov React, I went with PublishSubjects in the Components and calling onNext on specific label publishes from the store. Works well, but seems somewhat hacky, not sure why. I am subscribing once the component is mounted and that's it.

[Arkadii Ivanov]

Indeed it looks hacky. Looks like you can have val labels: Observable<Label> as part of the component's interface, and just write something like this in the component's impl:

override val labels: Observable<Label> = store.labels

Or if you want separate types, you can have something like this:

interface Some {
    val events: Observable<Event>

    sealed interface Event {
        object Success : Event
    }
}

class SomeComponent : Some {
    val store = ...

    override val events: Observable<Event> = store.labels.map(labelToComponentEvent)
}

internal val labelToComponentEvent: (Label) -> Event = {
    when (it) {
        is Label.Success -> Event.Success
    }
}

[Nikola Milovic]

Quick question, if I have a Label that should only notify the component to manipulate the router alongside UI Events like in the above example, I wouldn't be able to just directly map labels to events? Or I'd have to deal with the exhaustive warning for whens right?

Eg

Label {
 object ShowSomePopup // gets mapped to an event
 object CloseCurrentScreen // doesn't have an event tied to it
}

[Arkadii Ivanov]

You still can map directly. Your mapper function's result type should be nullable. And you can use mapNotNull operator.

[Arkadii Ivanov]

But it seems you don't need to map labels to manipulate the router. I would subscribe inside the component and use when and manipulate the router.