In compose version 0.3.0-build143 the onDispose function is replaced by DisposableEffect where a key is required. But in my use case i just want to do some cleanups when the composable is removed from the view tree. How can i implement this with the new API?

Can you elaborate on the type of cleanup you want to perform? It is our expectation that a

DisposableEffect

without a key would be rare, and would love to see details about any counterexample. With regards to your specific question though, I believe you can just pass in

Unit

as the key parameter, which will satisfy the compiler.

I do have a custom navigation framework. And a composable is used as root element for the navigation. Than when the app navigates to different screens a backstack is build up. When the root composable is disposed i want to reset the backstack.

For the first one, it sounds like the back stack object being reset on disposal is an appropriate key

I want to code a transition effect. So when the key changes i need to update the state of the transition object.

seems like what you're looking for is:

val ts = remember { ... }
SideEffect {
  ts.target = transition.data
}

setting

target

should skip if the new value is equal or invalidate as necessary

Is the code inside SideEffect is executed again if the MutableState of the variable transition is changed?

It is executed only after the current recomposition succeeds

Ok but than this code will not work.

If you were using the

onCommit

to observe a snapshot state object for changes to run some code when it does change, then you've encountered the antipattern that this API change was intended to break/make very awkward 🙂

Ok i see.

one way to do this is with `snapshotFlow`:

val ts = remember { ... }
LaunchedEffect(ts) {
  snapshotFlow { transition }.collect { newTransitionValue ->
    ts.newTarget(newTransitionValue.data)
    // ...
  }
}

I think i do have this code snippets from older implementations of Crossfade or other transition effect.

probably 🙂 we learned many of the antipatterns and why they're antipatterns the hard way in our own codebase

Ok i think i could do it than this way:

val ts = remember { ... }
if (ts.target != transition.data) {
    ts.target = transition.data
}

So long as `ts.target`'s set function has no other side effects beyond setting other snapshot state, that can work fine. If it does, you might be in for some correctness problems in the not too distant future, since composition can fail and you don't want lingering side effects that we can't roll back by discarding the current mutable snapshot in progress.

ok thx. I will try to fix my code 😄