LayoutAwareModifierNode

A androidx.compose.ui.Modifier.Node which receives various callbacks in response to local changes in layout.

This is the androidx.compose.ui.Modifier.Node equivalent of androidx.compose.ui.layout.OnRemeasuredModifier and androidx.compose.ui.layout.OnPlacedModifier

Example usage:

import androidx.compose.material.Text
import androidx.compose.ui.Modifier
import androidx.compose.ui.layout.onSizeChanged

// Use onSizeChanged() for diagnostics. Use Layout or SubcomposeLayout if you want
// to use the size of one component to affect the size of another component.
Text(
    "Hello $name",
    Modifier.onSizeChanged { size ->
        println("The size of the Text in pixels is $size")
    }
)
import androidx.compose.animation.core.Animatable
import androidx.compose.animation.core.AnimationVector2D
import androidx.compose.animation.core.Spring.StiffnessMediumLow
import androidx.compose.animation.core.VectorConverter
import androidx.compose.animation.core.spring
import androidx.compose.foundation.background
import androidx.compose.foundation.border
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.offset
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.layout.size
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.rememberCoroutineScope
import androidx.compose.ui.Alignment
import androidx.compose.ui.ExperimentalComposeUiApi
import androidx.compose.ui.Modifier
import androidx.compose.ui.composed
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.layout.onPlaced
import androidx.compose.ui.layout.positionInParent
import androidx.compose.ui.unit.IntOffset
import androidx.compose.ui.unit.dp
import androidx.compose.ui.unit.round

@OptIn(ExperimentalComposeUiApi::class)
fun Modifier.animatePlacement(): Modifier = composed {
    val scope = rememberCoroutineScope()
    var targetOffset by remember { mutableStateOf(IntOffset.Zero) }
    var animatable by remember {
        mutableStateOf<Animatable<IntOffset, AnimationVector2D>?>(null)
    }
    this.onPlaced {
        // Calculate the position in the parent layout
        targetOffset = it.positionInParent().round()
    }.offset {
        // Animate to the new target offset when alignment changes.
        val anim = animatable ?: Animatable(targetOffset, IntOffset.VectorConverter)
            .also { animatable = it }
        if (anim.targetValue != targetOffset) {
            scope.launch {
                anim.animateTo(targetOffset, spring(stiffness = StiffnessMediumLow))
            }
        }
        // Offset the child in the opposite direction to the targetOffset, and slowly catch
        // up to zero offset via an animation to achieve an overall animated movement.
        animatable?.let { it.value - targetOffset } ?: IntOffset.Zero
    }
}

@OptIn(ExperimentalComposeUiApi::class)
@Composable
fun AnimatedChildAlignment(alignment: Alignment) {
    Box(
        Modifier.fillMaxSize().padding(4.dp).border(1.dp, Color.Red)
    ) {
        Box(
            modifier = Modifier.animatePlacement().align(alignment).size(100.dp)
                .background(Color.Red)
        )
    }
}
import androidx.compose.ui.Modifier
import androidx.compose.ui.node.LayoutAwareModifierNode
import androidx.compose.ui.node.ModifierNodeElement
import androidx.compose.ui.platform.InspectorInfo
import androidx.compose.ui.unit.IntSize

class SizeLoggerNode(var id: String) : LayoutAwareModifierNode, Modifier.Node() {
    override fun onRemeasured(size: IntSize) {
        println("The size of $id was $size")
    }
}

data class LogSizeElement(val id: String) : ModifierNodeElement<SizeLoggerNode>() {
    override fun create(): SizeLoggerNode = SizeLoggerNode(id)
    override fun update(node: SizeLoggerNode) {
        node.id = id
    }
    override fun InspectorInfo.inspectableProperties() {
        name = "logSize"
        properties["id"] = id
    }
}

fun Modifier.logSize(id: String) = this then LogSizeElement(id)

Summary

Public functions
open Unit

onPlaced is called after the parent LayoutModifier and parent layout has been placed and before child LayoutModifier is placed.
Cmn
open Unit

This method is called when the layout content is remeasured.
Cmn

Inherited properties
From androidx.compose.ui.node.DelegatableNode
Modifier.Node

A reference of the Modifier.Node that holds this node's position in the node hierarchy.
Cmn

Public functions

onPlaced

Cmn
Added in 1.3.0
open fun onPlaced(coordinates: LayoutCoordinates): Unit

onPlaced is called after the parent LayoutModifier and parent layout has been placed and before child LayoutModifier is placed. This allows child LayoutModifier to adjust its own placement based on where the parent is.

If you only need to access the current LayoutCoordinates at a single point in time from outside this method, use currentLayoutCoordinates.

onRemeasured

Cmn 
open fun onRemeasured(size: IntSize): Unit

This method is called when the layout content is remeasured. The most common usage is onSizeChanged.