Is there a way for a newly added element to immediately read the layout bounds of its parent, and wh...

# compose

[Alexander Maryanovsky]

Is there a way for a newly added element to immediately read the layout bounds of its parent, and what is the best way in general to read that? Code inside.

[Alexander Maryanovsky]

e.g.

Box(Modifier.size(300.dp)) {
    if (showBox) {
        val parentLayoutBounds = ...
    }
}

We currently add an empty layout and attach this to it:

private inline fun Modifier.parentBoundsInWindow(
    crossinline onBoundsChanged: (IntRect) -> Unit
) = this.onPlaced { childCoordinates ->
    childCoordinates.parentCoordinates?.let {
        val layoutPosition = it.positionInWindow().round()
        val layoutSize = it.size
        onBoundsChanged(IntRect(layoutPosition, layoutSize))
    }
}

So:

var parentLayoutBounds: IntRect? by remember { mutableStateOf(null) }
EmptyLayout(Modifier.parentBoundsInWindow { parentLayoutBounds = it })

[Alexander Maryanovsky]

But this means we only know the bounds on the next recomposition (and we force a recomposition).

[Alexander Maryanovsky]

Hmm, maybe I just need to not read parentLayoutBounds in the composition

[Louis Pullen-Freilich [G]]

Yeah, if you do something with bounds in layout / draw it will be fine. As a general rule it's suspicious to need layout information in composition

[Alexander Maryanovsky]

Yeah, I just changed parentLayoutBounds to be a MutableState and passed that to the measure policy that needs it