Why `SideEffect` gets called ever-time my composab...

# compose

[ritesh]

Why SideEffect gets called ever-time my composable is invalidated , but same does-not hold true for LaunchedEffect?


Query in 🧵

[dewildte]

By design perhaps?

[ritesh]

Aren't effect handlers tied to composable life cycle? Probably i am missing something, in this scenario

[Alexander Maryanovsky]

That’s what LaunchedEffect does - it’s only executed once (every time the value of its key changes). SideEffect is executed on every recomposition.

[Alexander Maryanovsky]

https://developer.android.com/jetpack/compose/side-effects

[ritesh]

Yes, I understand the difference
SideEffect -> on every successful composition and re-composition, if it's part of it
LaunchedEffect -> when its enters composition and span across re-composition unless the keys are changed.

[ritesh]

But in above scenario - this code particularly

@Composable
fun MyTopLevelComposable(viewModel:MyViewModel){

  when (val state = viewModel.response.observeAsState().value) { // observing live-data state
    is Content -> LaunchedEffect(Unit) { launchActivity() }
    Error -> SideEffect { someDialog.value = true}
  }
}

It will never get recomposed. The only reason for this composable to be called again could be if compose compiler invalidates the view.

My Query is -> when view/composable gets invalidated

SideEffect {someDialog.value = true} executes, because it will again go through composition not re-composition as viewModel.response(which is live-data) last state was Error


But if change it to LaunchedEffect(Unit) {someDialog.value = true} it doesn't executes again after the composable is invalidated. It only reacts to a new state emitted by the live-data.
Question is why? Invalidate should start composition again, and since it's a composition. not re-composition LaunchedEffect should behave similarly to SideEffect in this scenario, as both are reaching to composition.

Or May be i am missing something here?

[ritesh]

Was answered here by @Philip Dukhov
https://stackoverflow.com/questions/71342736/issue-with-side-effects-launchedeffect-and-sideeffect-in-jetpack-compose/71374631?noredirect=1#co[…]631