Swiftui interaction footguns

SwiftUI Interaction Footguns

A class of bugs that look fine in code but break at runtime. These have shipped to production from real projects (see Sightings section). Sweep this checklist on every SwiftUI View review.

When to invoke

• Reviewing any new or modified SwiftUI View
• Reviewing Button / NavigationLink / TabView / Form / Menu
• Reviewing Mac variants (NavigationSplitView / sidebar)
• After a macOS or iPad smoke test surfaces a tap or navigation bug
• Before declaring a Phase complete that ships new View code

Checklist

Tap target & hit-test

• Button { } label: { LayoutWithSpacer } .buttonStyle(.plain) → hit-test shrinks to drawn content; the Spacer-expanded area is not tappable. Fix: .contentShape(Rectangle()) on the label's outermost container.
• Same trap for NavigationLink, Menu, and any custom interactive view with .onTapGesture + Spacer / frame(maxWidth: .infinity) / padding.
• Padding and frame(maxWidth: .infinity) enlarge the visual frame but do not automatically enlarge the hit region under .plain. When in doubt, add .contentShape.

NavigationSplitView (Mac / iPad)

• Sidebar items must be NavigationLink(value:) or Button — a bare Label is non-interactive even if it visually looks like a row.
• iPhone compact size class should fall back to NavigationStack, not split. Snapshot tests for iPhone fixtures must force .compact (see next item).
• Selection binding pitfall: sidebar selection and detail's path must share the same source of truth, or selection won't navigate.

horizontalSizeClass on Mac

• @Environment(\.horizontalSizeClass) returns .regular for every macOS-hosted SwiftUI view — even iPhone-shaped fixtures inside NSHostingView. iPhone snapshot tests must inject .compact explicitly via .environment(\.horizontalSizeClass, .compact).

Async state load timing

• .task { await viewModel.bootstrap() } re-fires on every view mount / identity change. If a test pre-seeds VM state, the task overwrites it back to .loading. Fix: hasBootstrapped latch in the VM + a separate retry() method for user-driven retry.
• .task(id:) cancels and restarts when id changes — confirm that's the intent.

Dynamic Type / AX3–AX5

• Do NOT gate layout on @Environment(\.dynamicTypeSize) inside a fullScreenCover / sheet modal. The env value can read a stale .large there even while the Text views actually scale via UIFont metrics — so a dynamicTypeSize.isAccessibilitySize ? VStack : HStack reflow never fires and labels still clip off-screen (negative-x frame). (Proved in a real project: a game board presented in a modal; cells/labels enlarged but the gate read .large.) Use a geometry-driven layout instead — ViewThatFits(in: .horizontal) { HStack; VStack } picks the row/column from the actual offered width, no env read.
• minimumScaleFactor is WIDTH-driven — it shrinks text too WIDE for its frame. It does not rescue a glyph that overflows vertically. A single digit "5" at AX5 is ~50–60pt tall in a 44pt pill → clipped top/bottom to a blank pill; minimumScaleFactor never engages and .frame(maxHeight:) alone just clips it.
• Fix for compact fixed-size controls (digit pad, board chrome/header) that must stay legible without honoring full AX scaling: cap the Dynamic Type — .dynamicTypeSize(...DynamicTypeSize.xLarge). The cap clamps only sizes ABOVE .xLarge, so default .large rendering — and committed snapshot baselines — stay byte-identical; surrounding content (e.g. 9×9 board cells) keeps scaling. Standard compact-numeric-control approach; geometry/UIFont-driven, so a modal's stale env can't defeat it.
• Snapshot tests do NOT prove a Dynamic Type fix. A snapshot that injects DynamicTypeSize.accessibility3 into an NSHostingView bypasses the modal env-propagation path and gives a false pass (real example: three rounds passed snapshots, all failed on device). idb-sim-verify AX4 AND AX5 on a booted sim (simctl ui <udid> content_size accessibility-extra-extra-large / …-extra-extra-extra-large), eyeball the screenshot — don't trust the injected-env snapshot. Size map: AX1=accessibility-medium, AX2=accessibility-large, AX3=accessibility-extra-large, AX4=accessibility-extra-extra-large, AX5=accessibility-extra-extra-extra-large.
• Keep grids and critical regions fixed-metric (e.g. 9×9 board uses fixed cell metrics); let body/label text scale.

Theme propagation to SwiftUI system controls

• Picker, Button(.borderedProminent), ProgressView, Toggle, Stepper etc. follow .tint / .accentColor. The project's theme.accent.primary does not auto-propagate — apply .tint(theme.accent.primary.resolved) on each system control or at a high-enough ancestor.

NSHostingView snapshot environment

• colorScheme override needs host.appearance = NSAppearance(named: ...) on macOS — SwiftUI's .preferredColorScheme does not propagate through NSHostingView.
• locale and horizontalSizeClass overrides must be set on the View before wrapping in NSHostingView; mutating after host creation is unreliable.

Button / Picker styling

• .labelsHidden() on Picker when the label is provided externally (avoids duplicated label rendering on Mac).
• .buttonStyle(.borderedProminent) honours .tint from iOS 15+ / macOS 12+; both APIs were introduced together in SwiftUI 3.
• .foregroundStyle(...) chained after .buttonStyle(.borderedProminent) on the Button itself is silently ignored — the prominent style keeps its own default label color, even though the code compiles and unit tests pass. Fix: apply .foregroundStyle to the label content inside the Button { } label: { … } closure, not chained on the Button call. Only a rendered screenshot exposes the ignored-placement variant.

.onAppear does not re-fire on fullScreenCover dismiss

• When a fullScreenCover dismisses back to its presenting view, that view's .onAppear does not re-fire — an .onAppear { refresh() } wired for "refresh when the user returns from the modal" silently never runs. (Verified on-device across repeated open/dismiss cycles; the only fresh .onAppear fire in that round-trip is a transient re-mount at open, not at dismiss.)
• Fix: drive post-dismiss refresh off an explicit teardown signal instead — a counter or flag the dismiss path sets, observed via .onChange, never .onAppear. Unit tests and code review both pass the wrong wiring; only an instrumented on-device or simulator run (a log probe in the refresh call, driving open→dismiss) exposes it.

Touch target minimums

• Apple HIG: 44×44pt minimum. Buttons that look smaller due to compact text + tight padding fail accessibility audit even if visually balanced.

View identity & if/else

• Branching between if A { ViewA } else { ViewB } gives the two branches distinct identities; state (@State, .task latches, focus) resets on switch. Use a single view with conditional modifiers when identity preservation matters.

Sheet / fullScreenCover presentation vs data race

• fullScreenCover(isPresented: $bool) / sheet(isPresented:) driven by a separate optional @State for the content, set back-to-back (data = x; isPresented = true), races: the cover presents from the Bool before the optional propagates into the content closure, so if let data { … } renders the empty branch → a blank cover. Looks correct in code; only a runtime drive (not snapshots, not unit tests) catches it. Fix: make the payload Identifiable and use fullScreenCover(item: $data) { data in … } — presentation and data are then atomic. (@MainActor payload → mark id nonisolated.)

@Observable + @Bindable

• Reading an @Observable model via let vm = … does not establish a binding scope; passing vm into a child that needs @Bindable var vm requires the child to redeclare with @Bindable. Forgetting this silently breaks two-way bindings (TextField, Toggle).
• Swift 6 mode: @Observable view-models accessed from a View body must themselves be @MainActor-isolated (or all accessed properties must be nonisolated). A non-isolated @Observable class causes "Sending 'X' risks causing data races" because View.body is @MainActor-isolated. Fix: annotate the view-model class with @MainActor.

View-model built inside a navigationDestination / factory closure

• A view-model constructed inline inside the .navigationDestination(for:) closure (or a RouteFactory.view(for:) that the destination calls) and stored as @Bindable is re-minted on every destination re-render — any parent re-render (e.g. an ad banner WebView finishing its load) gives the view a fresh .idle instance, and because the view keeps the same SwiftUI identity its .task { bootstrap() } does NOT re-fire, so it's stuck loading forever while the original (already-.loaded) instance is orphaned. Symptom: a screen stuck on its spinner even though the VM reached .loaded (confirm by logging ObjectIdentifier(self) in bootstrap() vs ObjectIdentifier(viewModel) in body — a vmid mismatch = orphaned VM). (Real-world example: same class of bug appears as "transient VM loses state" in multiple forms.) Fix: the destination view must own the VM via @State (first-value-wins: _viewModel = State(wrappedValue: viewModel)), so SwiftUI retains the first instance across destination re-invocations. Never @Bindable for a factory-built destination VM. This is a runtime-only bug — only an idb drive (often with network/ads active) catches it; offline it stays hidden.

How to apply

1. Before approving any PR touching SwiftUI Views, sweep the checklist mentally.
2. For each item that could apply, grep / re-read the diff for the trigger pattern.
3. If a footgun is present, flag it with a concrete fix (cite the bullet).

Sightings (real bugs that shipped past review)

• Tap-target shrink — A home screen mode card used Button { } label: { card-with-Spacer } with .buttonStyle(.plain), shrinking the tap target to drawn content only. Caught by macOS smoke test, not by Code Reviewer. Fix: .contentShape(Rectangle()).
• Inert sidebar Labels — Mac NavigationSplitView sidebar items were bare Labels with no NavigationLink / Button, so clicking did nothing. Same review-blind-spot path.
• Blank fullScreenCover — A near-win hook presented a blank fullScreenCover: fullScreenCover(isPresented: $bool) + a separate optional @State for content, set back-to-back, raced → content closure's if let rendered the empty branch (a11y tree = 1 element vs 99 for a real board). Dual-model CR + unit tests passed; only the idb interactive audit caught it. Fix: fullScreenCover(item:) with an Identifiable payload.

Related skills

• subagent-review-cycles — Code Reviewer dispatch brief should explicitly name this skill when reviewing SwiftUI Views.
• swiftui-expert-skill — broader domain skill (Instruments traces, hang/hitch profiling); different scope.
• swiftui-pro (aggregated external) — a broad "SwiftUI mistakes LLMs make" catalog (navigation/layout/animation/state/deprecated-API). This skill is the narrower complement: runtime-only bugs that shipped past code review in one project, each with a reproduction note (vmid logging, blank-fullScreenCover race, stale-modal Dynamic Type, idb-verify-not-snapshot). Use both.