Hello everybody I'm curious about why rememberUpda...

# compose

[Erfannj En]

Hello everybody
I'm curious about why rememberUpdatedState sets the value again after remembering.
It seems that without apply { value = newValue } there is no problem.

@Composable
public fun <T> rememberUpdatedState(newValue: T): State<T> =
    remember { mutableStateOf(newValue) }.apply { value = newValue }

[Alex Styl]

what is the question here?

[Alex Styl]

it sets the value so that it maintains the latest value. the remember part will not be called again, but the value = newValue can be called multiple times

[Erfannj En]

@Alex Styl
thanks

[Mohammad Fallah]

Hey Erfan,
if you remove the apply, then it will be a simple remember without a key, it means if the value that is passed to rememberUpdatedState get changed in the next recomposition it won't be stored in this state.

but you may argue why they didn't put a key then, the problem with remember (key) is that it will re-execute the block again, it means you will get a new state, it's a new reference, and if you already passed the previous state to somewhere, it won't be updated automatically,

for example, assume you have a component that do something after 5 seconds from the time it comes to the composition based on one of the arguments, so after 5 seconds you will check the argument.

@Composable
fun MySpecialComponent(doWhat : Int) {
    LaunchedEffect(Unit) {
        delay(5000)
        if (doWhat == 1) doSomething1()
        else if (doWhat == 2) doSomethingElse()
    }
}

It may look OK, but the problem is that what if the doWhat changes before the 5th second? e.g. the component comes to the composition with doWhat = 1 then after 1 second it will be updated to doWhat = 2?

you can solve this problem by

val currentDoWhat = rememberUpdatedState(doWhat)

then you can use currentDoWhat in LaunchedEffect.

[Zach Klippenstein (he/him) [MOD]]

That value set is the “update” part of “remember updated state”.

[Erfannj En]

@Mohammad Fallah Thank you very much for your complete answer.