How to get an attribute from a UI data class as a state in Composable? Say I have A class

data class A(val x: Int)

Inside the Composable:

@Composable
fun Test(vm: ViewModel){
  val a by vm.a.collectAsState()// I want x attribute not a object
}

Is there a way to accomplish that?

you can now write

a.x

where you wish to access the attribute

I know, but I want to use

x

to produce another value like:

val a vm.a.collectAsState()
val isXEqualsToZero by remember {
     derivedStateOf { a.x == 0 }
}

It's more convenient to get rid of

a

and use

x

directly

then you can write

val x = a.x

first, or wrap you code in

with (a) {...}

In that case, can I use it inside the

derivedStateOf

directly without creating another state for it? Idk if

snapShotFlow{}

can help in such cases

in what case?

That you mentioned,

x

in viewModel

im not sure what to tell you, if x is in the viewmodel you can do all the same things with it you can with a

Thank you, idk how I missed that!

isXEqualToZero = a.X == 0 will recompose more than you probably want

that screams premature optimisation to me, a small thing like that is basically guaranteed to not be a big deal unless a is changing very often

Do you know what he’s doing with X to claim its “screaming” premature optimization?

the point is more that

derivedStateOf

is only necessary when performance improvements are needed. as is repeated throughout compose documentation when performance is involved, optimisations should not be undertaken without there being evidence of an actual performance hit. compose is performant by default in the vast majority of cases, so its not really correct to say that

derivedStateOf

is the way to go.

X

here is a state that changed by clicking a button

it so often is 😛

not really, no wrt "it so often is" but all good