LazyHStack

Expo UI LazyHStack matches the official SwiftUI LazyHStack API and arranges its children horizontally, creating items only as needed (when they become visible during scrolling).

LazyHStack is not truly lazy yet: the native side only builds visible items, but React still creates every child up front, so large lists can be slow to mount. We are working on improving this. For large lists, we recommend FlashList or Legend List.

Usage

Basic lazy horizontal stack

LazyHStack should be used inside a ScrollView with axes="horizontal" to enable lazy rendering.

import {
  Host,
  ScrollView,
  LazyHStack,
  Text,
} from '@expo/ui/swift-ui';

export default function BasicLazyHStackExample() {
  return (
    <Host style={{ flex: 1 }}>
      <ScrollView axes="horizontal">
        <LazyHStack spacing={12}>
          {Array.from({ length: 100 }, (_, i) => (
            <Text key={i}>{`Item ${i}`}</Text>
          ))}
        </LazyHStack>
      </ScrollView>
    </Host>
  );
}

A horizontal row of items numbered zero to five, centered on the screen.

With alignment

The alignment prop controls vertical alignment of children. Available options are: top, center, bottom, firstTextBaseline, and lastTextBaseline.

import {
  Host,
  ScrollView,
  LazyHStack,
  Rectangle,
} from '@expo/ui/swift-ui';
import { frame } from '@expo/ui/swift-ui/modifiers';

export default function LazyHStackAlignmentExample() {
  return (
    <Host
      matchContents={{ horizontal: true }}
      style={{ flex: 1, alignSelf: 'center' }}>
      <ScrollView axes="horizontal">
        <LazyHStack spacing={12} alignment="top">
          <Rectangle
            modifiers={[frame({ width: 50, height: 50 })]}
          />
          <Rectangle
            modifiers={[frame({ width: 50, height: 100 })]}
          />
          <Rectangle
            modifiers={[frame({ width: 50, height: 75 })]}
          />
        </LazyHStack>
      </ScrollView>
    </Host>
  );
}

Three rectangles of different heights in a row, aligned along their top edges.

API

import { LazyHStack } from '@expo/ui/swift-ui';

Component

`LazyHStack`

Type: React.Element<LazyHStackProps>

LazyHStackProps

`alignment`

Optional • Literal type: string

The vertical alignment of children within the stack.

Acceptable values are: 'center' | 'top' | 'bottom' | 'firstTextBaseline' | 'lastTextBaseline'

`children`

Type: ReactNode

`spacing`

Optional • Type: number

The spacing between children.

Inherited props

CommonViewModifierProps

Modifiers

Use these modifiers in the modifiers prop of the SwiftUI version.

Expo UI lets you put any of the 89 modifiers for any view on LazyHStack, but not all of them do something here.

75 change what you see on LazyHStack.
2 work, but not in the way that you may expect.
1 have no visible effect on LazyHStack.
13 work only in one place, such as a widget or a Grid.

Modifier	What to know
`onLongPressGesture`	Touches on the empty space between children are not detected. Add `contentShape('rectangle')` before this modifier.
`onTapGesture`	Touches on the empty space between children are not detected. Add `contentShape('rectangle')` before this modifier.

No visible effect on LazyHStack

LazyHStack accepts these modifiers, but you see no change. They do not give an error.

Modifier	Why nothing happens
`zIndex`	It changes the order of views that cover each other in the same parent, and LazyHStack does not stack its children.

Only in some places

These modifiers work only in a widget, in a Grid, in a Namespace or in a parent that asks for them.

Modifier	Where it works
`activityBackgroundTint`	Works only in a Live Activity. It has no effect in the app.
`alignmentGuide`	Has an effect only when the parent, such as a `VStack` or `ZStack`, aligns its children by the same guide.
`containerBackground`	Works only in a widget, or in a navigation container when you use a `navigation` placement.
`glassEffectId`	Works only on a view that also has `glassEffect`, in a `GlassEffectContainer` and a `Namespace`.
`gridCellAnchor` iOS 16+	Works only on a cell of a `Grid`. `Grid` is in `@expo/ui/swift-ui`, but it has no Expo docs page.
`gridCellColumns`	Works only on a view in a `Grid.Row`. `Grid` is in `@expo/ui/swift-ui`, but it has no Expo docs page.
`gridCellUnsizedAxes`	Works only on a view in a `Grid`. `Grid` is in `@expo/ui/swift-ui`, but it has no Expo docs page.
`gridColumnAlignment` iOS 16+	Works only on a view in a `Grid.Row`. `Grid` is in `@expo/ui/swift-ui`, but it has no Expo docs page.
`invalidatableContent` iOS 17+	Has an effect only when a parent view uses `redacted` with the `invalidated` reason.
`matchedGeometryEffect`	Works only in a `Namespace`. Give two views the same `id` and change between them with an animation.
`privacySensitive`	Has an effect only when a parent view uses `redacted` with the `privacy` reason.
`unredacted`	Has an effect only in a parent view that uses `redacted`.
`widgetURL`	Works only in a widget. It has no effect in the app.

Sources

The original Expo docs for this page:

LazyHStack (SwiftUI) (source-of-truth/versions/v57.0.0/sdk/ui/swift-ui/lazyhstack.md)