How to get screen width and height in Compose Multiplatform?

Question

How can I get the screen size in Compose Multiplatform without using expect/actual?

I have found the following explanation in https://github.com/JetBrains/compose-multiplatform/discussions/3225#discussioncomment-7195192:

You can also use a Layout as your root Composable and obtain the size from the passed constraints. This solution doesn't depend on platform implementations and also gives you the exact size given to your Composable which could be different from the device screen size in some cases.

Once you have that size can use a CompositionLocal to pass it down the composable tree

I have not been able to fully understand or successfully implement the suggested layout.

Answer 1

I got the answer at https://github.com/JetBrains/compose-multiplatform/discussions/3225#discussioncomment-7386013

Using that I've created a small example that might be helpful for others looking for the answer:

import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.layout.Layout

@Composable
fun App() {
    val screenSize = remember { mutableStateOf(Pair(-1, -1)) }
    Layout(
        content = {
            Box(modifier = Modifier.fillMaxSize()) {
                Text("Screen size: ${screenSize.value.first}x${screenSize.value.second}px", modifier = Modifier.align(Alignment.Center))
            }
        },
        measurePolicy = { measurables, constraints ->
            // Use the max width and height from the constraints
            val width = constraints.maxWidth
            val height = constraints.maxHeight

            screenSize.value = Pair(width, height)
            println("Width: $width, height: $height")

            // Measure and place children composables
            val placeables = measurables.map { measurable ->
                measurable.measure(constraints)
            }

            layout(width, height) {
                var yPosition = 0
                placeables.forEach { placeable ->
                    placeable.placeRelative(x = 0, y = yPosition)
                    yPosition += placeable.height
                }
            }
        }
    )
}

Here's a screenshot of the code running on macOS, iOS simulator and Android emulator: