Navigate for result?

[JohnBuhanan]

Is there a way to navigate for result?

Something like this:

ScreenA goTo ScreenB
ScreenB set result
ScreenB pop
ScreenA gets result

[JohnBuhanan]

I figured the best way to forward this discussion was to take a stab at it.

I'm sure there is something wrong with this approach, but how's this?

interface ResultListener {
    val map: MutableMap<String, MutableState<*>>
}

@Singleton
@ContributesBinding(AppScope::class)
class ResultListenerImpl @Inject constructor() : ResultListener {
    override val map: MutableMap<String, MutableState<*>> = mutableMapOf()
}

inline fun <reified T> ResultListener.setResult(result: T) {
    val state: MutableState<T> = map[T::class.java.name]!! as MutableState<T>
    state.value = result
}

inline fun <reified T> ResultListener.onResult(default: T): MutableState<T> {
    map.putIfAbsent(T::class.java.name, mutableStateOf(default))
    val state = map[T::class.java.name]

    return state as MutableState<T>
}

And then it would be used as follows:

class FirstPresenter @Inject constructor(
    private val resultListener: ResultListener,
) : Presenter<FirstState> {
    @Composable
    override fun present(): FirstState {
        val resultFromSecondScreen by remember { resultListener.onResult<SecondResult?>(null) }  <--- listening for result
        ...
    }
}

class SecondPresenter @Inject constructor(
    private val resultListener: ResultListener,
    private val navigator: Navigator,
) : Presenter<SecondState> {
    @Composable
    override fun present(): SecondState {
        ...
        return SecondState(
            ...
        ) { event ->
            when (event) {
                SecondEvent.TappedThing -> {
                    resultListener.setResult(SecondResult("BLAH"))  <--- setting result
                    navigator.pop()
                }
            }
        }
    }
}

What would be wrong with this approach? Is there a better way?

[ZacSweers]

We've seen this come up several times, but every time it seems like it's just trying to replicate activity/fragment result APIs rather than seek something better. You should try using an Overlay or a composite presenter pattern, which we feel solves both of these much better.