SwiftUI Layout API Reference

Comprehensive API reference for SwiftUI adaptive layout tools.

Overview

Complete guide to all SwiftUI layout APIs for building adaptive interfaces, based on WWDC 2022, 2024, and 2025 content.

What This Reference Covers

Container Selection

• ViewThatFits – Automatic variant selection (iOS 16+)
• AnyLayout – Type-erased animated layout switching (iOS 16+)
• Layout Protocol – Custom layout algorithms (iOS 16+)

Geometry Reading

• onGeometryChange – Efficient geometry reading without layout side effects (iOS 16+ backported)
• GeometryReader – Layout-phase geometry access (iOS 13+)

Trait-Based Adaptation

• Size Classes – horizontalSizeClass, verticalSizeClass (coarse trait semantics, not a width sensor)
• Dynamic Type – dynamicTypeSize.isAccessibilitySize
• ScaledMetric – Scaled dimensions for accessibility

Window APIs

• Resizable windows everywhere – iPhone apps resize too (Mac mirroring, iPhone-only on iPad)
• onInteractiveResizeChange – Throttle work during a live resize drag (iOS 26+)
• Window resize anchor – Control resize animation origin
• Menu bar commands – iPad menu bar via .commands
• NavigationSplitView – Automatic column visibility

Key Patterns

ViewThatFits

ViewThatFits {
    HStack { content }  // First choice
    VStack { content }  // Fallback
}

AnyLayout

let layout = isCompact
    ? AnyLayout(VStackLayout())
    : AnyLayout(HStackLayout())
layout { content }
    .animation(.default, value: isCompact)

onGeometryChange

.onGeometryChange(for: CGSize.self) { proxy in
    proxy.size
} action: { size in
    self.containerSize = size
}

Size Class Truth Table (iPad)

Configuration	Horizontal	Vertical
Full screen (any)	.regular	.regular
70% Split View	.regular	.regular
50% Split View	.regular	.regular
33% Split View	.compact	.regular
Slide Over	.compact	.regular

Key insight: Size class only goes .compact on iPad at ~33% width.

This table describes an app under its native iPad idiom. An iPhone app in a resizable window — Mac mirroring, or iPhone-only on iPad — keeps the .phone idiom and stays .compact at every width. Size class will not flip to .regular no matter how wide the window gets, because iOS 27 decouples host semantics (idiom, size class) from available geometry. Drive your own width breakpoints from geometry (onGeometryChange) and reserve horizontalSizeClass for system-container semantics. See swiftui-layout for the "don't inject .regular to fake iPad" anti-pattern.

Related Resources

• swiftui-layout – Decision guidance and anti-patterns
• Apple Documentation: Layout Protocol
• Apple Documentation: ViewThatFits