My google-fu is failing me. What was the "new" way to observe android lifecycle events like onCreate...

# compose-android

[Colton Idle]

My google-fu is failing me. What was the "new" way to observe android lifecycle events like onCreate, onStart, etc in compose.

I used to use disposableEffect, but there was some artifact that was updated with this I recall...

[Pablichjenkov]

I don't think it is out yet, unless it was really recent

[Colton Idle]

too many release notes ive read. i forget whats what. 😂

[Ian Lake]

It was the 2.7.0-alpha01 release of lifecycle-runtime-compose that has the new LifecycleEventEffect for a single event and LifecycleStartEffect / LifecycleResumeEffect for a disposable effect style pair of events: https://developer.android.com/jetpack/androidx/releases/lifecycle#2.7.0-alpha01

[Colton Idle]

Do you by chance know if there are any sample usages of this. I can't seem to get LifecycleStartEffect to compile. feel like im mis-understanding something here

[Ian Lake]

You know how DisposableEffect needs to end in a onDispose block? LifecycleStartEffect needs to end in a onStopOrDispose block - that's the "pair of events" I mentioned: https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:lifecycl[…]idx/lifecycle/compose/samples/LifecycleComposeSamples.kt;l=92

[Colton Idle]

I'm going to test this out myself... but figured I'd ask since we have the thread going anyway.

Is this

LifecycleStartEffect {
            dataAnalytics.startTimeTracking()

            onStopOrDispose {
                timeTracker.stopTimeTracking()
            }
        }

equivallent to this?

LifecycleEventEffect(Lifecycle.Event.ON_START){
dataAnalytics.startTimeTracking()
  }

LifecycleEventEffect(Lifecycle.Event.ON_STOP){
dataAnalytics.stopTimeTracking()
  }

[Ian Lake]

The OrDispose part of onStopOrDispose should be a clue on where they differ: if the LifecycleStartEffect is removed from composition (say, it is inside an if statement that changes from true to false) before the Lifecycle is stopped, the onStopOrDispose block will still fire, ensuring the cleanup of whatever you did before that block is guaranteed to run if you ever got STARTED.

Having two separate blocks won't have that property - if you put your code in separate LifecycleEventEffect blocks, there's no coupling between them and thus no guaranteed cleanup

[Marcin Wisniowski]

@Ian Lake The onStopOrDispose gets called twice (if you navigate out of a screen, it gets fired both for the STOP lifecycle event, and again for being disposed) which is a problem if the cleanup is not idempotent. Is this intended?

In the above example stopTimeTracking() would get called twice which depending on the implementation may be a problem, where having the two separate `LifecycleEventEffect`s doesn't have that problem.

[Ian Lake]

It should only fire once, please file a bug if you're seeing something different: https://issuetracker.google.com/issues/new?component=413132

[Marcin Wisniowski]

https://issuetracker.google.com/issues/352364595