`derivedStateOf` vs `remember` . When should I prefer one over the other?

# compose

[Dominaezzz]

derivedStateOf vs remember . When should I prefer one over the other?

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

derivedStateOf is for when you need to read State objects to calculate your value. If you already have a State, it might be a good fit. Remember takes explicit keys, so it can handle that as well but is a bit more verbose.

If you find yourself writing something like

val input: State<Int> = …
val

state by remember {

mutableStateOf(input.value * 2)
}.apply { value = input.value * 2 }

hen it might be time for derivedStateOf

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

Wow slack is useless, just ate an entire paragraph I typed in that message 🤦‍♂️

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

Anyway if you excuse that garbage formatting, if you’re remembering a mutable state and updating it yourself, that’s when you might be able to use derivedStateOf

[Dominaezzz]

Ah thanks. I'll be using that derivedStateOf more now.

[Orhan Tozan]

From what I remember, you don't need derivedStateOf. You can just do val sum = a + b

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

Yes, for this example, you can just do the calculation. In a real use case, you’d presumably be doing some more expensive calculation.