Adaptive Layout — iPhone & iPad

Core Principle

Let SwiftUI adapt automatically. Never check UIDevice.current.userInterfaceIdiom or UIScreen.main.bounds for layout decisions. Use size classes and adaptive containers instead.

Navigation

NavigationSplitView (primary pattern for list-detail)

Use NavigationSplitView for ANY list-detail flow. It collapses to NavigationStack on iPhone and shows sidebar+detail on iPad — zero conditional code.

@State private var selectedItem: Item?

NavigationSplitView {
    List(items, selection: $selectedItem) { item in
        NavigationLink(value: item) { ItemRow(item: item) }
    }
    .navigationTitle("Items")
} detail: {
    if let selectedItem {
        ItemDetailView(item: selectedItem)
    } else {
        ContentUnavailableView("Select an Item", systemImage: "doc")
    }
}

Three-column pattern (sidebar categories → list → detail):

NavigationSplitView {
    List(categories, selection: $selectedCategory) { ... }
} content: {
    List(filteredItems, selection: $selectedItem) { ... }
} detail: {
    if let selectedItem { DetailView(item: selectedItem) }
    else { ContentUnavailableView(...) }
}

Use NavigationStack ONLY for purely linear flows (onboarding, checkout).

Size Classes

@Environment(\.horizontalSizeClass) private var horizontalSizeClass

| Context | horizontalSizeClass | |---|---| | iPhone portrait | .compact | | iPhone landscape | .compact | | iPad full-screen | .regular | | iPad Split View (narrow) | .compact | | iPad Split View (wide) | .regular |

Critical: iPad in Split View multitasking can report .compact. This is why UIDevice.current is wrong — always use size classes.

Switching layout axis:

@Environment(\.horizontalSizeClass) private var sizeClass

var body: some View {
    let layout = sizeClass == .compact
        ? AnyLayout(VStackLayout(spacing: 16))
        : AnyLayout(HStackLayout(spacing: 24))
    layout {
        ContentBlockA()
        ContentBlockB()
    }
}

ViewThatFits (component-level adaptation)

Use when the decision is purely about available space — no environment reading needed:

ViewThatFits {
    HStack(spacing: 16) { icon; title; subtitle; actionButton }
    VStack(alignment: .leading, spacing: 8) {
        HStack { icon; title }
        subtitle
        actionButton
    }
}

When to use which:

• ViewThatFits → component-level (a card, a header, a toolbar item)
• horizontalSizeClass → screen-level (different page structures)

Adaptive Grids

Always use GridItem(.adaptive(minimum:maximum:)) — never hardcode column counts:

LazyVGrid(
    columns: [GridItem(.adaptive(minimum: 160, maximum: 320))],
    spacing: 16
) {
    ForEach(items) { item in CardView(item: item) }
}
.padding()

Automatically: 2 columns on iPhone, 3-4 on iPad portrait, 4-6 on iPad landscape.

Presentations — Sheet & Popover

Popovers auto-adapt

.popover(isPresented: $showOptions) {
    OptionsView()
}

• iPad (regular): floating popover anchored to source
• iPhone (compact): automatically becomes a sheet

Sheet behavior

.sheet(isPresented: $showSheet) {
    SheetContent()
        .presentationDetents([.medium, .large])
        .presentationDragIndicator(.visible)
}

• iPhone portrait: respects detents
• iPad wide: centered floating modal (detents ignored)

Confirmation dialogs

Always use .confirmationDialog — it becomes an action sheet on iPhone, popover on iPad:

.confirmationDialog("Options", isPresented: $showDialog) {
    Button("Option A") { }
    Button("Cancel", role: .cancel) { }
}

Spacing & Readability

• Use .padding() with no arguments — SwiftUI applies 16pt on iPhone, 20pt on iPad automatically.
• For long-form text on wide screens, constrain readability:

ScrollView {
    content
        .frame(maxWidth: 700)
        .frame(maxWidth: .infinity)
}

• Use @ScaledMetric for custom dimensions that respect Dynamic Type:

@ScaledMetric(relativeTo: .body) private var iconSize: CGFloat = 24

Relative Sizing

Prefer containerRelativeFrame over GeometryReader:

Image("photo")
    .containerRelativeFrame(.horizontal, count: 3, span: 1, spacing: 16)

Reserve GeometryReader only for complex calculations (parallax, custom alignment).

STRICT RULES

1. NEVER use UIDevice.current.userInterfaceIdiom for layout — breaks iPad multitasking
2. NEVER use UIScreen.main.bounds for sizing — doesn't respond to multitasking
3. NEVER use #if targetEnvironment for layout decisions
4. NEVER hardcode frame widths (e.g., .frame(width: 375))
5. NEVER hardcode grid column counts — use .adaptive(minimum:)
6. ALWAYS use Dynamic Type text styles (.font(.body), .font(.title))
7. ALWAYS provide a detail placeholder in NavigationSplitView for iPad empty state
8. ALWAYS use .popover for contextual actions — SwiftUI auto-adapts
9. ALWAYS use .leading/.trailing — never .left/.right