feat(api): RowBuilder.verticalAlign(...) — cross-axis row child alignment#239
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A row sizes its band to the tallest child, but shorter children always sat
flush with the band top; aligning a small label beside a large price, or an
icon with a line of text, meant computing offsets by hand.
verticalAlign(RowVerticalAlign.{TOP, CENTER, BOTTOM}) seats a row's children
on the cross axis within the band — the align-items analogue for a horizontal
row. The default is TOP, and the measure phase is untouched, so an existing
row computes the same band height and places its children byte-for-byte as
before; only CENTER/BOTTOM shift a child, by the band slack (accounting for
the child's own margin). Applies to both leaf and container children.
BASELINE is intentionally omitted for now — first-line ascent is not carried
through the measure result, so it cannot be honoured without a measure-layer
change; the enum admits it additively later.
Tests: RowVerticalAlignTest seats a short child beside a 60pt-tall one and
asserts its bottom lands 40 / 20 / 0 pt above the tall child's for TOP /
CENTER / BOTTOM, covers a container child at CENTER and a child whose own
bottom margin offsets BOTTOM, and confirms the default and the back-compat
RowNode constructor resolve to TOP. Example: RowVerticalAlignExample (a price
row at all three alignments). Full suite green, no visual baselines changed.
The cross-axis offset subtracts the child margin from the band slack; add a comment that the measure phase guarantees that slack stays non-negative (the band is the tallest child's margin-box), so the offset never lifts a child above the band top.
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Why
A row sizes its band to the tallest child, but shorter children always sat flush with the band top. Aligning a small
/monthlabel beside a large price, or an icon with a line of text, meant computing vertical offsets by hand.What changed
RowBuilder.verticalAlign(RowVerticalAlign.{TOP, CENTER, BOTTOM})— seats a row's children on the cross axis within the band (height = tallest child). Thealign-itemsanalogue for a horizontal row, no manual coordinates. Applies to both leaf and container children.TOPis the default and the measure phase is untouched — an existing row computes the same band height and places its children byte-for-byte as before. OnlyCENTER/BOTTOMshift a child, by the band slack (accounting for the child's own margin). The seating computes a0.0offset forTOP, so the placement expression is bit-identical to the pre-feature code.BASELINEis intentionally omitted — first-line ascent is not carried throughMeasureResult, so it cannot be honoured without a measure-layer change. The enum admits it additively later.This is the cross-axis half of the row-layout work; flex-spacer + main-axis arrangement (
pushRight,SPACE_BETWEEN, …) is a separate follow-up that touches the width-distribution lockstep.Lane: canonical DSL (
RowBuilder,RowVerticalAlign,RowNode) + a 2-line shared-engine seating change. Purely additive → japicmp-safe (the newRowNodecomponent is gated behind re-declared back-compat delegating constructors).Verification
./mvnw test -pl .— green, 0 changed visual baselines → existing (TOP) rows render identically../mvnw -P japicmp verify— binary-compatible.RowVerticalAlignTest(7): a short child beside a 60pt-tall one lands 40 / 20 / 0 pt above the tall child's bottom forTOP / CENTER / BOTTOM; a container child seats atCENTER; a child's own bottom margin offsetsBOTTOM; the default and the back-compatRowNodeconstructor resolve toTOP.TOPbyte-identity (including the-0.0edge), the offset math incl. margins, and the delegating-ctor chain; it drove the composite-child + margined-child tests.RowVerticalAlignExample+ committed preview: a$49 / monthrow at all three alignments.