launchInComposition is gone? Why?

# compose

[Mehdi Haghgoo]

launchInComposition is gone? Why?

[Timo Drick]

It is renamed to LaunchedEffect

[Mehdi Haghgoo]

What is subject parameter in LaunchedEffect for? What should be passed in?

[Timo Drick]

when you pass mutalbestate variables the effect will start every time the variable changed

[Adam Powell]

Passing MutableState values as LaunchedEffect params is generally a code smell indicating that you're using the effect recomposition as a change observer

[Adam Powell]

You'll usually pass the object you're working with inside the effect

[Mehdi Haghgoo]

Does this have anything to do with coroutines?

[Timo Drick]

It is launched as a coroutine which is bound to the lifecycle of the composable

[Adam Powell]

As an example, the various flow collect extensions are implemented like this:

var currentValue by remember { mutableStateOf(initialValue) }
LaunchedEffect(myFlow) {
  myFlow
    .map { performSomeMappingOf(it) }
    .collect { currentValue = it }
}

[Adam Powell]

the flow object itself is used as the key/subject parameter to LaunchedEffect, so if you recompose with a different myFlow, it cancels the old collect operation and starts a new one with the new value of myFlow

[Adam Powell]

people tended to forget to think about keys with launchInComposition so it's required now. If you really have no keys and you want it to last initial composition to full removal from composition, you can write LaunchedEffect(true) or LaunchedEffect(Unit) - just like a while (true) loop, this should always make you look a little bit closer to be sure it's what the author really intended to do.