iOS Application Development Guide

A practical guide for building iOS applications using UIKit, SnapKit, and SwiftUI. Focuses on proven patterns and Apple platform conventions.

Routing Boundary

Use this skill for native iOS/iPadOS apps, Swift, SwiftUI, UIKit, SnapKit, Apple platform APIs, App Store UI expectations, and iOS accessibility. Use android-native-dev for native Android, flutter-dev for Flutter/Dart, react-native-dev for React Native/Expo, and frontend web skills for browser React/Next/Vue UI.

Quick Reference

Implementation Workflow

1. Inspect the app boundary: identify SwiftUI vs UIKit ownership, deployment target, package manager, navigation root, design system, accessibility patterns, and nearest tests before editing.
2. Choose SwiftUI or UIKit with the decision table below; keep mixed apps at their existing seam instead of moving screens across frameworks.
3. Implement one screen/flow at a time: data model or view model first, navigation/presentation second, layout third, accessibility/privacy states fourth.
4. Build and test: run the narrowest available Xcode scheme/test target; for UI-only changes, also inspect Dynamic Type, Dark Mode, VoiceOver labels, and reduced motion behavior.
5. Report platform evidence: include scheme/device or simulator used, tests run, and any manual checks that could not be executed.

🔴 CHECKPOINT · 🛑 STOP before changing navigation roots, permission timing, authentication/sign-in behavior, App Store-facing privacy behavior, or converting a screen between SwiftUI and UIKit. These are product/API decisions, not local UI cleanup.

SwiftUI vs UIKit Decision Table

Situation	Use	Avoid
New simple screen in SwiftUI app	View + @StateObject/@Observable pattern already present	Introducing UIKit controller just for layout convenience
Existing UIKit feature	UIViewController, UICollectionView, SnapKit, existing coordinator	Rewriting to SwiftUI unless migration is requested
Complex collection/grid	Existing UIKit compositional layout or SwiftUI Grid/List if app already uses it	Mixing two list systems in one screen
Deep navigation/state restoration	Existing UINavigationController/coordinator or NavigationStack pattern	Ad-hoc modal chains without back path
Custom drawing/animation	Core Animation/UIKit when precision is needed; SwiftUI animation for simple state transitions	Decorative motion that ignores Reduce Motion

Failure Modes and Fallbacks

Trigger	First response	If still failing
Xcode build fails from signing/provisioning	Separate code errors from signing errors; verify compile diagnostics first	Report signing as environment-blocked; do not change bundle IDs or teams
SwiftUI preview fails	Run the scheme/tests instead of treating preview failure as runtime truth	Mark preview-only issue separately if app builds
Auto Layout warnings appear	Identify the exact conflicting constraint and adjust local priorities/anchors	Do not silence by lowering many priorities; stop if layout ownership is unclear
Dynamic Type truncates content	Reflow layout, allow multiline text, or adjust stack priorities	Report if product copy/visual design must change
Permission prompt behavior is unclear	Inspect existing permission wrapper and Info.plist strings	Stop before changing request timing or privacy copy
UI test is flaky	Re-run once, check accessibility identifiers and async waits	Report flake evidence; do not add arbitrary sleeps

Do Not Do This

• Do not use hamburger/drawer navigation in native iOS flows.
• Do not override system back gestures or remove standard dismissal paths.
• Do not request camera/location/notification permissions at launch unless explicitly required.
• Do not use hard-coded colors/fonts that break Dark Mode or Dynamic Type.
• Do not change signing, entitlements, bundle identifiers, or privacy prompts as a side effect of UI work.

UIKit

Purpose	Component
Main sections	UITabBarController
Drill-down	UINavigationController
Focused task	Sheet presentation
Critical choice	UIAlertController
Secondary actions	UIContextMenuInteraction
List content	UICollectionView + DiffableDataSource
Sectioned list	DiffableDataSource + headerMode
Grid layout	UICollectionViewCompositionalLayout
Search	UISearchController
Share	UIActivityViewController
Location (once)	CLLocationButton
Feedback	UIImpactFeedbackGenerator
Linear layout	UIStackView
Custom shapes	CAShapeLayer + UIBezierPath
Gradients	CAGradientLayer
Modern buttons	UIButton.Configuration
Dynamic text	UIFontMetrics + preferredFont
Dark mode	Semantic colors (.systemBackground, .label)
Permissions	Contextual request + AVCaptureDevice
Lifecycle	UIApplication notifications

SwiftUI

Purpose	Component
Main sections	TabView + tabItem
Drill-down	NavigationStack + NavigationPath
Focused task	.sheet + presentationDetents
Critical choice	.alert
Secondary actions	.contextMenu
List content	List + .insetGrouped
Search	.searchable
Share	ShareLink
Location (once)	LocationButton
Feedback	UIImpactFeedbackGenerator
Progress (known)	ProgressView(value:total:)
Progress (unknown)	ProgressView()
Dynamic text	.font(.body) semantic styles
Dark mode	.primary, .secondary, Color(.systemBackground)
Scene lifecycle	@Environment(\.scenePhase)
Reduce motion	@Environment(\.accessibilityReduceMotion)
Dynamic type	@Environment(\.dynamicTypeSize)

Core Principles

Layout

• Touch targets >= 44pt
• Content within safe areas (SwiftUI respects by default, use .ignoresSafeArea() only for backgrounds)
• Use 8pt spacing increments (8, 16, 24, 32, 40, 48)
• Primary actions in thumb zone
• Support all screen sizes (iPhone SE 375pt to Pro Max 430pt)

Typography

• UIKit: preferredFont(forTextStyle:) + adjustsFontForContentSizeCategory = true
• SwiftUI: semantic text styles .headline, .body, .caption
• Custom fonts: UIFontMetrics / Font.custom(_:size:relativeTo:)
• Adapt layout at accessibility sizes (minimum 11pt)

Colors

• Use semantic system colors (.systemBackground, .label, .primary, .secondary)
• Asset catalog variants for custom colors (Any/Dark Appearance)
• No color-only information (pair with icons or text)
• Contrast ratio >= 4.5:1 for normal text, 3:1 for large text

Accessibility

• Labels on icon buttons (.accessibilityLabel())
• Reduce motion respected (@Environment(\.accessibilityReduceMotion))
• Logical reading order (.accessibilitySortPriority())
• Support Bold Text, Increase Contrast preferences

Navigation

• Tab bar (3-5 sections) stays visible during navigation
• Back swipe works (never override system gestures)
• State preserved across tabs (@SceneStorage, @State)
• Never use hamburger menus

Privacy & Permissions

• Request permissions in context (not at launch)
• Custom explanation before system dialog
• Support Sign in with Apple
• Respect ATT denial

Checklist

Layout

• Touch targets >= 44pt
• Content within safe areas
• Primary actions in thumb zone (bottom half)
• Flexible widths for all screen sizes (SE to Pro Max)
• Spacing aligns to 8pt grid

Typography

• Semantic text styles or UIFontMetrics-scaled custom fonts
• Dynamic Type supported up to accessibility sizes
• Layouts reflow at large sizes (no truncation)
• Minimum text size 11pt

Colors

• Semantic system colors or light/dark asset variants
• Dark Mode is intentional (not just inverted)
• No color-only information
• Text contrast >= 4.5:1 (normal) / 3:1 (large)
• Single accent color for interactive elements

Accessibility

• VoiceOver labels on all interactive elements
• Logical reading order
• Bold Text preference respected
• Reduce Motion disables decorative animations
• All gestures have alternative access paths

Navigation

• Tab bar for 3-5 top-level sections
• No hamburger/drawer menus
• Tab bar stays visible during navigation
• Back swipe works throughout
• State preserved across tabs

Components

• Alerts for critical decisions only
• Sheets have dismiss path (button and/or swipe)
• List rows >= 44pt tall
• Destructive buttons use .destructive role

Privacy

• Permissions requested in context (not at launch)
• Custom explanation before system permission dialog
• Sign in with Apple offered with other providers
• Basic features usable without account
• ATT prompt shown if tracking, denial respected

System Integration

• App handles interruptions gracefully (calls, background, Siri)
• App content indexed for Spotlight
• Share Sheet available for shareable content

References

Topic	Reference
Touch Targets, Safe Area, CollectionView	Layout System
TabBar, NavigationController, Modal	Navigation Patterns
StackView, Button, Alert, Search, ContextMenu	UIKit Components
CAShapeLayer, CAGradientLayer, Core Animation	Graphics & Animation
Dynamic Type, Semantic Colors, VoiceOver	Accessibility
Permissions, Location, Share, Lifecycle, Haptics	System Integration
Metal Shaders & GPU	Metal Shader Reference
SwiftUI HIG, Components, Patterns, Anti-Patterns	SwiftUI Design Guidelines
Optionals, Protocols, async/await, ARC, Error Handling	Swift Coding Standards

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Swift, SwiftUI, UIKit, SF Symbols, Metal, and Apple are trademarks of Apple Inc. SnapKit is a trademark of its respective owners.