Activity Result API

[brewin]

I wonder if it would be possible to add bindings for the new Activity Result API? It would be nice to have if there's a clean way to do it.

I made a quick attempt, but it doesn't work because registerForActivityResult must be called before STARTED and there doesn't seem to be any way to add callbacks after registering.

fun <I, O> ActivityResultCaller.activityResults(contract: ActivityResultContract<I, O>) = callbackFlow {
        val launcher = registerForActivityResult(contract) { result ->
            safeOffer(result)
        }
        awaitClose { launcher.unregister() }
    }

fun <I, O> ActivityResultCaller.launchForActivityResults(contract: ActivityResultContract<I, O>, input: I) =
    registerForActivityResult(contract) {}.launch(input)

LifecycleOwner is attempting to register while current state is RESUMED. LifecycleOwners must call register before they are STARTED

Nice work on the 1.0 release!

[ychescale9]

I'm not familiar with the Activity Result API, but looks like you have to hold onto the launcher: ActivityResultLauncher object to call launch() separately? So I'm not sure how we can abstract this workflow in a single Flow.

[brewin]

You're right. I was thinking multiple callbacks would be called for the same contract with different launchers. But that's not the case. So I guess there isn't any clean way to do it with a single extension function.

I ended up just using a MutableSharedFlow.

class MainActivity : AppCompatActivity() {
    
    private val permissionsResults = MutableSharedFlow<Map<String, Boolean>>(1)
    private val permissionsLauncher = registerForActivityResult(
        ActivityResultContracts.RequestMultiplePermissions(),
        permissionsResults::tryEmit
    )

    ...

For fun, here's an ugly way to do it with a single extension function...

class LauncherAndResults<I, O>(val launcher: ActivityResultLauncher<I>, val results: Flow<O>)

fun <I, O> ActivityResultCaller.launcherAndResults(
    contract: ActivityResultContract<I, O>
): LauncherAndResults<I, O> {
    val results = MutableSharedFlow<O>(1)
    val launcher = registerForActivityResult(contract, results::tryEmit)
    return LauncherAndResults(launcher, results)
}