---
title: "AlignmentLine"
description: "Defines an offset line that can be used by parent layouts to align and position their children.
Text baselines are representative examples of [AlignmentLine]s. For example, they can be used by
`Row`, to align its children by baseline, or by `paddingFrom` to achieve a layout with a specific
distance from the top to the baseline of the text content. [AlignmentLine]s can be understood as
an abstraction over text baselines.

When a layout provides a value for a particular [AlignmentLine], this can be read by the parents
of the layout after measuring, using the [Placeable.get] operator on the corresponding
[Placeable] instance. Based on the position of the [AlignmentLine], the parents can then decide
the positioning of the children.

Note that when a layout provides a value for an [AlignmentLine], this will be automatically
inherited by the layout's parent, which will offset the value by the position of the child within
itself. This way, nested layout hierarchies are able to preserve the [AlignmentLine]s defined for
deeply nested children, making it possible for non-direct parents to use these for positioning
and alignment. When a layout inherits multiple values for the same [AlignmentLine] from different
children, the position of the line within the layout will be computed by merging the children
values using the provided [merger]. If a layout provides a value for an [AlignmentLine], this
will always be the position of the line, regardless of the values provided by children for the
same line.

[AlignmentLine]s cannot be created directly, please create [VerticalAlignmentLine] or
[HorizontalAlignmentLine] instances instead."
type: "class"
---

<div class='type'>Class</div>


<a id='references'></a>

<div class='sourceset sourceset-common'>Common</div>


```kotlin
sealed class AlignmentLine(internal val merger: (Int, Int) -> Int)
```


Defines an offset line that can be used by parent layouts to align and position their children.
Text baselines are representative examples of `AlignmentLine`s. For example, they can be used by
`Row`, to align its children by baseline, or by `paddingFrom` to achieve a layout with a specific
distance from the top to the baseline of the text content. `AlignmentLine`s can be understood as
an abstraction over text baselines.

When a layout provides a value for a particular `AlignmentLine`, this can be read by the parents
of the layout after measuring, using the `Placeable.get` operator on the corresponding
`Placeable` instance. Based on the position of the `AlignmentLine`, the parents can then decide
the positioning of the children.

Note that when a layout provides a value for an `AlignmentLine`, this will be automatically
inherited by the layout's parent, which will offset the value by the position of the child within
itself. This way, nested layout hierarchies are able to preserve the `AlignmentLine`s defined for
deeply nested children, making it possible for non-direct parents to use these for positioning
and alignment. When a layout inherits multiple values for the same `AlignmentLine` from different
children, the position of the line within the layout will be computed by merging the children
values using the provided `merger`. If a layout provides a value for an `AlignmentLine`, this
will always be the position of the line, regardless of the values provided by children for the
same line.

`AlignmentLine`s cannot be created directly, please create `VerticalAlignmentLine` or
`HorizontalAlignmentLine` instances instead.


## Companion Object

#### Properties

<div class='sourceset sourceset-common'>Common</div>


```kotlin
const val Unspecified = Int.MIN_VALUE
```


Constant representing that an `AlignmentLine` has not been provided.





## Code Examples

### AlignmentLineSample
```kotlin
@Composable
fun AlignmentLineSample() {
    // Create a horizontal alignment line. Note it is not common for alignment lines to be created
    // in the scope of one composable, since they are usually used across more than one function.
    // We use ::min as merging strategy, which means that the parent will have the minimum of
    // the values of the alignment line, when this is inherited from more than one child.
    val exampleLine = remember { HorizontalAlignmentLine(::min) }
    // A layout with a fixed size, and a given position for the exampleLine alignment line.
    @Composable
    fun LineProviderLayout(exampleLinePosition: Int) {
        val size: Int = 20
        Layout({}) { _, _ -> layout(size, size, mapOf(exampleLine to exampleLinePosition)) {} }
    }
    Layout({
        LineProviderLayout(exampleLinePosition = 5)
        LineProviderLayout(exampleLinePosition = 10)
    }) { measurables, constraints ->
        val placeables = measurables.map { it.measure(constraints) }
        // placeables[0][line] will be 5
        // placeables[1][line] will be 10
        layout(constraints.maxWidth, constraints.maxHeight) {
            placeables[0].place(0, 3)
            placeables[1].place(constraints.maxWidth / 2, 0)
        }
    }
    // Note that if the parent of this Layout (the parent of AlignmentLineSample) was able to
    // query its position of exampleLine (assuming this was in a shared scope), its position would
    // be 8. This is because the Layout positioned its first child at 3 from the top,
    // and because of the ::min merging strategy the position of exampleLine will be
    // min(5 + 3, 10 + 0).
}
```