How are people handling permission flows with comp...

# compose

[Daniel]

How are people handling permission flows with compose? Right now I'm creating methods on my activity like ensureFineLocation that handles the whole permission flow and then passing a reference to the function down through the composables.

This seems like it will scale pretty badly though, both in that the activity has a lot of unrelated methods and I've got to pass a lot of free functions.

Also, since registerForActivityResult is global state I'm not sure the right way to handle repeated calls. I'm currently using a MutableState like so

private val fineLocationStatus = MutableState<Boolean?>(null)
    private val requestFineLocationLauncher =
        registerForActivityResult(ActivityResultContracts.RequestPermission()) { isGranted ->
            fineLocationStatus.value = isGranted
        }

   private fun ensureFineLocation(): Boolean {
       val initialCached = fineLocationStatus.value
       if (initialCached != null) {
           if (!initialCached) showFineLocationMissingError()
           return initialCached
       }

       val permission = Manifest.permission.ACCESS_FINE_LOCATION

        if (checkSelfPermission(permission) == PackageManager.PERMISSION_GRANTED) return true

        if (shouldShowRequestPermissionRationale(permission)) {
            if (!fineLocationRationalePrompt()) {
                fineLocationDeniedMsg()
                return false
            }
        }

        requestFineLocationLauncher.launch(permission)

        val cached = fineLocationStatus.filterNotNull().first()
        if (!cached) fineLocationDeniedMsg()
        return cached
   }

This is a little racy if there are multiple calls before a value is cached. I'm also not sure the value should be cached, so I considered clearing the mutable state before returning. Then I think I'd need to protect ensureFineLocation with a mutex, though.

I feel like there has to be a better solution. Is there a reason why registerForActivityResult uses a global callback instead of giving each request a different requestCode so that you can have a suspend fun like launcher.awaitResult?

[Ian Lake]

As per the docs (https://developer.android.com/training/basics/intents/result#register), your app can be killed due to low memory or config changes while the permission request (which is another activity) is in progress. You can't assume that your context exists at all after you call launch

[Daniel]

Oh, I hadn't realized the full implications of that. I don't understand then how it's possible to prompt for a permission on a button press in compose at all then

[Ian Lake]

And I think you're misunderstanding how rememberLauncherForActivityResult works (note: the method was renamed) - it is not a global callback at all, it automatically handles returning the result to specifically the launcher that you call launch on

[Ian Lake]

The reason it was renamed was specifically to denote that the launcher is remembered

[Daniel]

Thank you! I didn't realize there was a compose-specific activityResult api, I've been using the androidx version in my main activity and passing callbacks to control it

[Ian Lake]

Yep, use that: https://developer.android.com/reference/kotlin/androidx/activity/compose/package-summary#rememberlauncherforactivityresult

[Daniel]

I don't understand how that can work though @Ian Lake? My understanding is that remember doesn't persist through config changes/process death

[Ian Lake]

It uses rememberSaveable for the unique key

[Daniel]

But not the callback?

[Daniel]

Throughout my app I've been following the advice to configure not to restart on config changes and only using remember, not rememberSaveable. If I use this do I have to refactor everything to use rememberSaveable?

[Ian Lake]

You still should handle process death and recreation (something you can test with the 'Don't keep activities' developer option). You'd save a considerably less amount of data than you'd remember though

[Daniel]

Thanks for all the help

[Ian Lake]

We're tracking more comprehensive docs on the activity-compose APIs in https://issuetracker.google.com/190615266 if you'd like to star that and get notified on when those docs become available

[Manuel Vivo]

FYI, we’re working on permissions support in Accompanist 🙂