When Compose recomposes based on new inputs, it only calls the functions or lambdas that might have changed, and skips the rest.

Why is the root Compose function

RecompositionBehavior

always recomposed while the

Switch

only changes the input of

MaterialTheme

?

@Preview("RecompositionBehavior")
@Composable
fun RecompositionBehavior() {
    Log.d("Recompose", "RecompositionBehavior")
    var darkTheme by remember { mutableStateOf(false) }
    MaterialTheme(
        colors = if (darkTheme) darkColors else lightColors,
    ) {
        Log.d("Recompose", "MaterialTheme")
        Surface {
            Switch(checked = darkTheme, onCheckedChange = { darkTheme = it })
        }
    }
}

the remembered

darkTheme

property is inside the

RecompositionBehavior

block, so the whole block gets recomposed afaik

@Sebastian Kaspari But when I move

darkTheme

from

RecompositionBehavior

to the

MaterialTheme

block,

MaterialTheme

does’t get recomposed when

darkTheme

is changed. Why?

@Preview("RecompositionBehavior")
@Composable
fun RecompositionBehavior() {
    Log.d("Recompose", "RecompositionBehavior")
    MaterialTheme(
        colors = darkColors,
    ) {
        var darkTheme by remember { mutableStateOf(false) }
        Log.d("Recompose", "MaterialTheme")
        Surface {
            Switch(checked = darkTheme, onCheckedChange = { darkTheme = it })
        }
    }
}