I need to do something when a screen is shown (nav...

# compose

[Marcin Wisniowski]

I need to do something when a screen is shown (navigated to, or navigated back to, or the user returned from another app, etc.), which I would normally do in onStart. However I'm trying to build a full Compose app and using Compose Navigation, so the Activity lifecycle events not longer relate to the screens in the Compose world. What would be the correct alternative?

[Ian Lake]

Did you see the example in the docs for listening for Lifecycle events?

[Ian Lake]

Navigation Compose gives each screen its own Lifecycle, so the LocalLifecycleOwner being used there isn't the activity if you are on one of the screens inside a NavHost

[Marcin Wisniowski]

Ohh I see. I saw that I can listen for the lifecycle events but thought they wouldn't be useful as the Activity is resumed the entire time I'm navigating around. Thank you.

[Ian Lake]

FWIW, this upcoming change will allow you to write:

LifecycleEventEffect(Lifecycle.Event.ON_START) {
  // Do your onStart side effect here
}

[Ian Lake]

So it'll be a lot easier in just a few weeks 🙂

[Marcin Wisniowski]

Sweet, I borrowed the implementation from that change and it works great, thanks. When it gets released I can just delete my copy. 😄

[dewildte]

Awesome!!

[Ian Lake]

There's a couple of other neat things going into the overarching bug - a lifecycle.currentStateAsState which converts Lifecycle.State into observable Compose State (e.g., it will automatically trigger recomposition when the Lifecycle.State changes and the upcoming LifecycleStartEvent and LifecycleResumeEvent that give DisposableEffect style pairs of `onStart`/`onStop` and `onResume`/`onPause` calls for automatic cleanup style work

[Pablichjenkov]

Would that deprecate the collectAsStateWithLifecycle? Or perhaps not deprecate it but change the internal implementation of it?
Last time I checked, current implementation relied on listening the lifecycle events and starting/canceling a collecting job when start/stop respectively.

[Ian Lake]

No, no changes planned there - that API is built upon repeatOnLifecycle, which we're happy with the implementation with already (and doesn't depend on Compose, so can't use most of what we're building at this level)

[Pablichjenkov]

Makes sense

[Kata]

This looks really nice. I was waiting for this commit to be released https://github.com/androidx/androidx/commit/b75b447af3d27aed4b4bc5a826e6e92cd0aaff34 but this would be even better. Any plans for the release? Seems like there were no releases for the lifecycle library since march

[Colton Idle]

Was this ever released? my google-fu is failing me

[Kata]

Nope, and no info on when it will be released https://issuetracker.google.com/issues/235529345?pli=1

[Ian Lake]

In Lifecycle 2.7.0-alpha01, just like the issue says

[Colton Idle]

yeah. just saw that in the issuetracker link. Thanks!