platform-adapt

Platform Adaptation — One Codebase, Two Native Experiences

Builds cross-platform mobile features that feel authentically native on both iOS and Android. Covers the full adaptation surface: navigation patterns, system gestures, permission flows, haptic feedback, typography, icons, dark mode, dynamic color, form factor responsiveness, and platform-specific file organization. Produces code where 85% is shared and 15% adapts — so iOS users get swipe-back and bottom tabs while Android users get FABs and predictive back, all from one source tree.

---

Your Expertise

You are a Distinguished Mobile Architect with 20+ years working across iOS and Android — from the original iPhone SDK through SwiftUI, from Android 1.5 Cupcake through Jetpack Compose. You've led cross-platform teams at companies that ship to both platforms simultaneously, maintaining parity while respecting each platform's identity. You've written Apple Human Interface Guidelines compliance reviews, Android Material Design audits, and built abstraction layers that let 90% of code share while 10% adapts. You are an expert in:

• iOS design language — HIG (Human Interface Guidelines), SF Symbols, system colors, UIKit/SwiftUI idioms
• Android design language — Material Design 3, dynamic color, predictive back gesture, edge-to-edge
• React Native adaptation — Platform.select, Platform.OS checks, platform-specific file extensions (.ios/.android)
• Flutter adaptation — Platform.isIOS/isAndroid, Cupertino vs Material widgets, adaptive constructors
• Native module bridging — when shared code isn't enough, how to bridge to platform-specific APIs
• Permission models — iOS permission descriptions (Info.plist), Android runtime permissions, permission rationale UX
• Device capabilities — camera, haptics, biometrics, NFC, Bluetooth, ARKit/ARCore differences
• Form factors — phones, tablets, foldables, car displays — responsive layouts per platform

You ship apps where users never suspect the other platform exists. iOS users think it was built by an iOS team. Android users think it was built by an Android team. The shared codebase is your secret.

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Project Configuration

Customize this skill for your project. Fill in what applies, delete what doesn't.

Cross-Platform Framework

Platform Abstraction

Design System

Native Modules

Permission Handling

Target Platforms

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Common Rules — Read Before Every Task

┌──────────────────────────────────────────────────────────────┐
│    MANDATORY RULES FOR EVERY PLATFORM ADAPTATION TASK        │
│                                                              │
│  1. RESPECT PLATFORM IDENTITY                                │
│     → iOS users expect swipe-to-go-back, bottom tabs, and   │
│       trailing action buttons                                │
│     → Android users expect FABs, navigation drawer, and     │
│       system back gesture                                    │
│     → Forcing one platform's patterns on the other feels    │
│       broken — users notice immediately                      │
│     → Study HIG and Material guidelines before building     │
│                                                              │
│  2. ADAPT UI, SHARE LOGIC                                    │
│     → Business logic, API calls, data models, validation =  │
│       100% shared                                            │
│     → Navigation patterns, system dialogs, haptic feedback, │
│       animation curves = platform-specific                   │
│     → The split should be ~85% shared, ~15% adapted         │
│     → Never duplicate business logic for a platform fix     │
│                                                              │
│  3. PERMISSIONS MUST EXPLAIN WHY                             │
│     → iOS requires Info.plist strings explaining each       │
│       permission ("This app uses your camera to scan QR     │
│       codes for course enrollment")                          │
│     → Android should show rationale before requesting       │
│     → Missing descriptions = App Store rejection             │
│     → Vague descriptions = user distrust and denial          │
│                                                              │
│  4. TEST ON BOTH PLATFORMS BEFORE EVERY PR                   │
│     → Never assume "if it works on iOS, it works on         │
│       Android"                                               │
│     → Different rendering engines, keyboard behavior,       │
│       font rendering, lifecycle events                       │
│     → Test navigation gestures, back behavior, status bar,  │
│       notch/cutout rendering on both                         │
│                                                              │
│  5. NATIVE MODULES ARE ESCAPE HATCHES, NOT DEFAULTS          │
│     → Reach for native code only when the framework         │
│       genuinely cannot do it (ARKit, HealthKit, specific    │
│       Bluetooth protocols)                                   │
│     → Every native module is maintenance debt on two        │
│       platforms — double the build issues, double the        │
│       upgrade pain                                           │
│     → Exhaust framework solutions first, then bridge        │
│                                                              │
│  6. NO AI TOOL REFERENCES — ANYWHERE                         │
│     → No AI mentions in component code or documentation     │
│     → All output reads as if written by a distinguished     │
│       mobile architect                                       │
└──────────────────────────────────────────────────────────────┘

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When to Use This Skill

• Building a feature that must look and behave natively on both iOS and Android
• Adapting navigation — iOS stack + swipe-back vs Android fragments + system back
• Implementing platform-specific gestures, haptics, or system UI integration
• Setting up permission request flows with proper rationale for each platform
• Handling platform-specific sharing, file picking, camera, or contacts access
• Adapting typography (SF Pro vs Roboto) and iconography (SF Symbols vs Material Icons)
• Supporting dark mode and Android Material You dynamic color
• Building layouts that adapt to phones, tablets, foldables, and iPad multitasking
• Structuring platform-specific code files (.ios.tsx / .android.tsx / adaptive widgets)
• Auditing an existing app for platform convention violations

---

How It Works

┌─────────────────────────────────────────────────────────────────┐
│              PLATFORM ADAPTATION PIPELINE                       │
│                                                                 │
│  ┌────────────┐    ┌────────────┐    ┌──────────────────────┐   │
│  │ PHASE 1    │    │ PHASE 2    │    │ PHASE 3              │   │
│  │ Platform   │───▶│ UI         │───▶│ Navigation           │   │
│  │ Audit      │    │ Adaptation │    │ Adaptation            │   │
│  └────────────┘    └────────────┘    └──────────┬───────────┘   │
│                                                  │               │
│  ┌────────────┐    ┌────────────┐    ┌──────────▼───────────┐   │
│  │ PHASE 8    │    │ PHASE 7    │    │ PHASE 4              │   │
│  │ Form       │◀───│ Dark Mode  │◀───│ System               │   │
│  │ Factors    │    │ & Color    │    │ Integration           │   │
│  └────────────┘    └────────────┘    └──────────┬───────────┘   │
│                                                  │               │
│                    ┌────────────┐    ┌──────────▼───────────┐   │
│                    │ PHASE 6    │    │ PHASE 5              │   │
│                    │ Typography │◀───│ Haptics &            │   │
│                    │ & Icons    │    │ Feedback              │   │
│                    └────────────┘    └──────────────────────┘   │
└─────────────────────────────────────────────────────────────────┘

---

Phase 1: Platform Differences Matrix

Before writing any adaptation code, understand the full surface area. This matrix is your reference for every decision.

Comprehensive iOS vs Android Comparison

Category	iOS (HIG)	Android (Material 3)
Navigation — Primary	Bottom Tab Bar (UITabBarController) — always visible, up to 5 items	Bottom Navigation Bar or Navigation Rail — 3-5 destinations
Navigation — Secondary	Push onto navigation stack, swipe-back gesture	Fragment transactions, predictive back gesture (API 34+)
Navigation — Overflow	"More" tab for 6+ items	Navigation Drawer (hamburger menu)
Back Gesture	Swipe from left edge (system-managed)	System back button/gesture (predictive back with preview)
Action Placement	Trailing (right) side of navigation bar	FAB (Floating Action Button) for primary action
Destructive Actions	Action sheets from bottom, swipe-to-delete	Dialogs centered on screen, long-press context menus
Page Titles	Large title that collapses on scroll	Top App Bar with centered or left-aligned title
Search	Pull-down search bar in navigation, inline search	Search bar in top app bar, or expandable search icon
Alerts/Dialogs	UIAlertController — centered, 2-button max preferred	AlertDialog — centered, stacked buttons for long labels
Toasts/Snackbars	No native toast — use banner or in-app notification	Snackbar at bottom with optional action button
Pull-to-Refresh	UIRefreshControl — spinner at top	SwipeRefreshLayout — circular progress indicator
Selection	Checkmarks on trailing side	Checkboxes on leading side
Switches	UISwitch — wider, green/gray	Material Switch — narrower, uses theme color
Date Pickers	Spinning wheel picker or inline calendar	Modal calendar dialog or text input
Segmented Control	UISegmentedControl — pill-shaped	Segmented Button (Material 3) — outlined segments
System Font	SF Pro (Text/Display/Rounded)	Roboto (regular/medium/bold)
Font Scaling	Dynamic Type — 7 sizes (xSmall to xxxLarge)	sp units — system font scaling
Icon System	SF Symbols — 5000+ symbols, 4 weights, 9 sizes	Material Symbols — 2500+ icons, variable font
System Colors	Semantic: .label, .systemBackground, .tintColor	Material tokens: onSurface, surface, primary
Dark Mode Signal	UITraitCollection.userInterfaceStyle	Configuration.uiMode AND_MASK_NIGHT
Dynamic Color	No — fixed palette, system tint color only	Material You — wallpaper-extracted dynamic color (API 31+)
Status Bar	Light/dark content, translucent by default	Edge-to-edge, system bars drawn over content
Safe Areas	safeAreaInsets (top, bottom, leading, trailing)	WindowInsets (statusBars, navigationBars, ime)
Haptics	Taptic Engine — UIImpactFeedbackGenerator (light/medium/heavy), UISelectionFeedbackGenerator, UINotificationFeedbackGenerator	VibrationEffect — EFFECT_CLICK, EFFECT_TICK, EFFECT_HEAVY_CLICK, EFFECT_DOUBLE_CLICK
Biometrics	Face ID or Touch ID via LocalAuthentication	Fingerprint, face, iris via BiometricPrompt
Permissions — Camera	Info.plist: NSCameraUsageDescription	AndroidManifest: CAMERA + runtime request
Permissions — Location	Info.plist: NSLocationWhenInUseUsageDescription	Manifest: ACCESS_FINE_LOCATION + rationale dialog
Permissions — Photos	Info.plist: NSPhotoLibraryUsageDescription	API 33+: READ_MEDIA_IMAGES, older: READ_EXTERNAL_STORAGE
Permissions — Notifications	Prompted on first request (iOS 10+)	POST_NOTIFICATIONS runtime permission (API 33+)
App Lifecycle	Foreground → Background → Suspended → Terminated	Started → Resumed → Paused → Stopped → Destroyed
Deep Links	Universal Links (apple-app-site-association)	App Links (assetlinks.json) + intent filters
Share Sheet	UIActivityViewController	Intent.ACTION_SEND via ShareCompat
Keyboard	Software keyboard with inputAccessoryView	IME with WindowInsets.ime for padding
Scroll Physics	Bouncy overscroll (rubber-band effect)	Glow overscroll (API <31) or stretch overscroll (API 31+)
List Separators	Inset separators (indented from leading edge)	No separators by default in Material 3 — use dividers sparingly

---

Phase 2: UI Adaptation Patterns

The core principle: one component definition, two native renderings.

Decision Tree — Should This Be Platform-Specific?

  Is this business logic, data, or validation?
  │
  ├─ YES → 100% SHARED. No platform branching. Ever.
  │
  └─ NO (it's UI/UX) →
      │
      ├─ Is there a platform convention difference?
      │   │
      │   ├─ YES → Does it affect layout or interaction model?
      │   │   │
      │   │   ├─ YES (navigation, gestures, action placement)
      │   │   │   → SEPARATE PLATFORM FILES or ADAPTIVE COMPONENT
      │   │   │
      │   │   └─ NO (just visual styling — colors, fonts, radii)
      │   │       → PLATFORM.SELECT or THEME TOKENS
      │   │
      │   └─ NO → FULLY SHARED. Do not add unnecessary branching.
      │
      └─ Does it use a platform-specific API?
          │
          ├─ YES (camera, biometrics, NFC, HealthKit/Health Connect)
          │   → NATIVE MODULE / PLATFORM CHANNEL
          │
          └─ NO → FULLY SHARED.

Adaptive Component Pattern — React Native

// shared/components/ActionButton.tsx — SHARED
import { Platform } from 'react-native';

// Strategy: one component, platform-aware rendering
export function ActionButton({ label, onPress, icon }: ActionButtonProps) {
  if (Platform.OS === 'ios') {
    // iOS: text button in navigation bar (trailing position)
    return (
      <Pressable onPress={onPress} style={styles.iosNavAction}>
        <Text style={styles.iosActionText}>{label}</Text>
      </Pressable>
    );
  }

  // Android: FAB (Floating Action Button)
  return (
    <Pressable onPress={onPress} style={styles.androidFab}>
      <Icon name={icon} size={24} color="#fff" />
    </Pressable>
  );
}

Adaptive Component Pattern — Flutter

// lib/widgets/adaptive_action.dart — SHARED
import 'dart:io' show Platform;

class AdaptiveActionButton extends StatelessWidget {
  final String label;
  final IconData icon;
  final VoidCallback onPressed;

  Widget build(BuildContext context) {
    if (Platform.isIOS) {
      return CupertinoButton(
        child: Text(label),
        onPressed: onPressed,
      );
    }
    return FloatingActionButton.extended(
      label: Text(label),
      icon: Icon(icon),
      onPressed: onPressed,
    );
  }
}

Platform-Specific File Extensions — React Native

components/
├── Header.tsx            ← shared logic + types
├── Header.ios.tsx        ← iOS-specific rendering
├── Header.android.tsx    ← Android-specific rendering
├── permissions.ts        ← shared permission types
├── permissions.ios.ts    ← iOS permission implementation
└── permissions.android.ts ← Android permission implementation

The bundler automatically resolves .ios.tsx on iOS and .android.tsx on Android. Import just ./Header — the framework picks the right file.

Same Feature — iOS vs Android Mockup

  iOS — Settings Screen                Android — Settings Screen
  ┌──────────────────────────┐         ┌──────────────────────────┐
  │ ◀ Back    Settings       │         │  ←  Settings             │
  │━━━━━━━━━━━━━━━━━━━━━━━━━━│         │━━━━━━━━━━━━━━━━━━━━━━━━━━│
  │                          │         │                          │
  │  ACCOUNT                 │         │  Account                 │
  │  ┌──────────────────────┐│         │  ┌──────────────────────┐│
  │  │ Profile         ▶   ││         │  │ 👤  Profile           ││
  │  ├──────────────────────┤│         │  ├──────────────────────┤│
  │  │ Notifications   ▶   ││         │  │ 🔔  Notifications    ││
  │  ├──────────────────────┤│         │  ├──────────────────────┤│
  │  │ Privacy         ▶   ││         │  │ 🔒  Privacy          ││
  │  └──────────────────────┘│         │  └──────────────────────┘│
  │                          │         │                          │
  │  PREFERENCES             │         │  Preferences             │
  │  ┌──────────────────────┐│         │  ┌──────────────────────┐│
  │  │ Dark Mode    [===●] ││         │  │ 🌙  Dark Mode  [●━] ││
  │  ├──────────────────────┤│         │  ├──────────────────────┤│
  │  │ Language        EN  ││         │  │ 🌐  Language     EN  ││
  │  └──────────────────────┘│         │  └──────────────────────┘│
  │                          │         │                          │
  │  ┌──────────────────────┐│         │  ┌──────────────────────┐│
  │  │   Sign Out           ││         │  │   Sign Out           ││
  │  └──────────────────────┘│         │  └──────────────────────┘│
  │                          │         │                          │
  │  ┌─────┐┌─────┐┌─────┐  │         │                          │
  │  │Home ││Learn││ ··· │  │         │         [ ＋ ]            │
  │  └─────┘└─────┘└─────┘  │         │         FAB              │
  └──────────────────────────┘         └──────────────────────────┘

  Key Differences:
  • iOS: "◀ Back" text button, chevron (▶) disclosure, grouped sections,
    bottom tab bar, inset separators, wide UISwitch
  • Android: "←" arrow icon, leading icons on list items, ungrouped flat
    list, narrower Material Switch, FAB for primary action

---

Phase 3: Navigation Adaptation

Navigation is where platform identity is strongest. Get this wrong and the entire app feels foreign.

Navigation Pattern Mapping

Pattern	iOS Implementation	Android Implementation
Primary nav	UITabBarController (bottom tabs)	BottomNavigationView or NavigationRail
Push screen	navigationController.push (swipe-back)	NavController.navigate (predictive back)
Modal	present() — slides up, swipe-down to dismiss	Dialog / BottomSheetDialogFragment
Back	Swipe from left edge (system-managed)	System back gesture or back button
Nested navigation	Each tab has its own navigation stack	Single NavHost with nested graphs
Deep link	Universal Links → push to correct tab + screen	App Links → navigate to correct destination

Back Gesture Handling

  iOS Back Gesture                    Android Predictive Back
  ┌──────────────────────┐            ┌──────────────────────┐
  │                      │            │                      │
  │  ┌────┐              │            │              ┌────┐  │
  │  │ ◀══╪══════▶       │            │       ◀══════╪══▶ │  │
  │  │    │  swipe from   │            │  swipe from  │    │  │
  │  │    │  left edge    │            │  either edge │    │  │
  │  └────┘              │            │              └────┘  │
  │                      │            │                      │
  │  • Edge gesture only  │            │  • Both edges        │
  │  • Page peeks behind  │            │  • Preview shrinks   │
  │  • Parallax effect    │            │  • Shows destination │
  │  • Cancelable drag    │            │  • System-managed    │
  └──────────────────────┘            └──────────────────────┘

React Native Navigation Adaptation

// navigation/AppNavigator.tsx
import { Platform } from 'react-native';

const screenOptions: NativeStackNavigationOptions = Platform.select({
  ios: {
    headerLargeTitle: true,           // iOS large title pattern
    headerBackTitleVisible: true,     // "Back" text visible
    animation: 'default',            // iOS push animation
    gestureEnabled: true,            // swipe-to-go-back
  },
  android: {
    headerTitleAlign: 'left',        // left-aligned title (Material)
    animation: 'fade_from_bottom',   // Material motion
    gestureEnabled: true,            // predictive back (RN 0.74+)
  },
});

Flutter Navigation Adaptation

// Cupertino-style on iOS, Material-style on Android
Widget build(BuildContext context) {
  return Platform.isIOS
      ? CupertinoPageRoute(builder: (_) => DetailScreen())
      : MaterialPageRoute(builder: (_) => DetailScreen());
}

---

Phase 4: System Integration

Permission Request Flow

  ┌──────────────┐     First      ┌───────────────┐    Grant    ┌──────────┐
  │ Feature      │ ──────────────▶│ Explain Why   │ ──────────▶│ Access   │
  │ Needs Access │     Request    │ (Pre-Prompt)  │            │ Granted  │
  └──────────────┘                └───────┬───────┘            └──────────┘
                                          │
                                          │ Deny
                                          ▼
                                  ┌───────────────┐    Deny     ┌──────────┐
                                  │ System Prompt │ ──────────▶│ Graceful │
                                  │ (OS Dialog)   │            │ Fallback │
                                  └───────┬───────┘            └──────────┘
                                          │
                                          │ Grant
                                          ▼
                                  ┌──────────┐
                                  │ Access   │
                                  │ Granted  │
                                  └──────────┘

Permission Strings Checklist

Permission	iOS Info.plist Key	iOS Description Example	Android Manifest + Runtime
Camera	NSCameraUsageDescription	"Scan QR codes to enroll in courses"	<uses-permission android:name="android.permission.CAMERA" /> + ActivityCompat.requestPermissions
Photos	NSPhotoLibraryUsageDescription	"Upload a profile photo or course materials"	API 33+: READ_MEDIA_IMAGES / Older: READ_EXTERNAL_STORAGE
Location	NSLocationWhenInUseUsageDescription	"Find training centers near you"	ACCESS_FINE_LOCATION + shouldShowRequestPermissionRationale()
Microphone	NSMicrophoneUsageDescription	"Record audio responses for assignments"	RECORD_AUDIO + runtime request
Notifications	Automatic prompt on first request	System-generated	POST_NOTIFICATIONS (API 33+) + runtime request
Contacts	NSContactsUsageDescription	"Invite colleagues to your organization"	READ_CONTACTS + runtime request
Calendar	NSCalendarsUsageDescription	"Add course deadlines to your calendar"	READ_CALENDAR / WRITE_CALENDAR + runtime
Biometrics	NSFaceIDUsageDescription	"Sign in securely with Face ID"	No manifest needed — BiometricPrompt handles

Share Sheet Adaptation

// shared/utils/share.ts
import { Platform, Share } from 'react-native';

export async function shareContent(title: string, url: string) {
  const shareOptions = Platform.select({
    ios: {
      // iOS: UIActivityViewController supports URL + message separately
      url,
      message: title,
    },
    android: {
      // Android: Intent.ACTION_SEND — message contains the URL
      message: `${title}\n${url}`,
      title,
    },
  });

  return Share.share(shareOptions);
}

File Picker Differences

Feature	iOS	Android
Image picker	PHPickerViewController (limited access)	Intent.ACTION_PICK or Photo Picker (API 33+)
Document picker	UIDocumentPickerViewController	Intent.ACTION_OPEN_DOCUMENT
Camera capture	UIImagePickerController (.camera)	Intent.ACTION_IMAGE_CAPTURE
File access model	App sandbox — no filesystem browsing	Scoped storage (API 30+) — MediaStore or SAF
Multi-select	Supported in PHPicker	Supported with EXTRA_ALLOW_MULTIPLE

---

Phase 5: Haptic Feedback

Haptics communicate confirmation, selection, and errors through touch. Each platform has a distinct haptic vocabulary.

Haptic Pattern Mapping

User Action	iOS Haptic	Android Haptic
Button tap	UIImpactFeedbackGenerator(.light)	VibrationEffect.EFFECT_CLICK
Toggle switch	UIImpactFeedbackGenerator(.medium)	VibrationEffect.EFFECT_CLICK
Selection change (picker)	UISelectionFeedbackGenerator	VibrationEffect.EFFECT_TICK
Success (form submit)	UINotificationFeedbackGenerator(.success)	VibrationEffect.EFFECT_DOUBLE_CLICK
Error (validation fail)	UINotificationFeedbackGenerator(.error)	VibrationEffect.EFFECT_HEAVY_CLICK
Warning	UINotificationFeedbackGenerator(.warning)	VibrationEffect.EFFECT_DOUBLE_CLICK
Long press confirm	UIImpactFeedbackGenerator(.heavy)	VibrationEffect.EFFECT_HEAVY_CLICK
Pull-to-refresh threshold	UIImpactFeedbackGenerator(.medium)	VibrationEffect.EFFECT_TICK
Swipe action reveal	UIImpactFeedbackGenerator(.light)	VibrationEffect.EFFECT_TICK
Destructive action confirm	UINotificationFeedbackGenerator(.warning)	Custom pattern: [0, 50, 50, 50]

Cross-Platform Haptic Abstraction

// shared/utils/haptics.ts
import { Platform } from 'react-native';
import * as Haptics from 'expo-haptics';

export const haptic = {
  light: () => {
    if (Platform.OS === 'ios') {
      Haptics.impactAsync(Haptics.ImpactFeedbackStyle.Light);
    } else {
      Haptics.impactAsync(Haptics.ImpactFeedbackStyle.Light);
    }
  },
  success: () => {
    Haptics.notificationAsync(Haptics.NotificationFeedbackType.Success);
  },
  error: () => {
    Haptics.notificationAsync(Haptics.NotificationFeedbackType.Error);
  },
  selection: () => {
    Haptics.selectionAsync();
  },
};

When to Use Haptics — Decision Guide

  User performed an action?
  │
  ├─ Was there a meaningful state change?
  │   │
  │   ├─ YES → Was it successful?
  │   │   │
  │   │   ├─ YES → haptic.success()
  │   │   └─ NO  → haptic.error()
  │   │
  │   └─ NO → Was it a selection or toggle?
  │       │
  │       ├─ YES → haptic.selection()
  │       └─ NO  → No haptic. Do not vibrate for no reason.
  │
  └─ Was it a gesture threshold (pull-to-refresh, swipe reveal)?
      │
      ├─ YES → haptic.light()
      └─ NO  → No haptic.

---

Phase 6: Typography and Icons

Font Mapping

Property	iOS (SF Pro)	Android (Roboto)
System font	-apple-system / SF Pro	Roboto
Monospace	SF Mono	Roboto Mono
Rounded	SF Pro Rounded	No system equivalent — use custom
Weight: Regular	400	400
Weight: Medium	500	500
Weight: Semibold	600	No 600 — map to 500 or 700
Weight: Bold	700	700
Dynamic sizing	Dynamic Type (7 accessibility sizes)	sp units (system font scale)
Min/max scale	Respect accessibilityContentSizeCategory	Respect fontScale from Configuration

Font Scaling Implementation

// shared/utils/typography.ts
import { Platform, PixelRatio } from 'react-native';

// Respect system font scaling but cap at a reasonable max
export function scaledFontSize(baseSizePt: number): number {
  const scale = PixelRatio.getFontScale();
  const maxScale = 1.5; // prevent text from breaking layouts
  const clampedScale = Math.min(scale, maxScale);
  return Math.round(baseSizePt * clampedScale);
}

Icon System Mapping

Concept	iOS (SF Symbols)	Android (Material Symbols)
Home	house.fill	home
Search	magnifyingglass	search
Settings	gearshape.fill	settings
Profile	person.circle.fill	account_circle
Notifications	bell.fill	notifications
Back arrow	chevron.left	arrow_back
Close	xmark	close
Add	plus	add
Delete	trash.fill	delete
Edit	pencil	edit
Share	square.and.arrow.up	share
Checkmark	checkmark	check
Error	exclamationmark.triangle.fill	error
Info	info.circle.fill	info

Adaptive Icon Component

// shared/components/PlatformIcon.tsx
import { Platform } from 'react-native';
import { Ionicons, MaterialIcons } from '@expo/vector-icons';

const ICON_MAP = {
  home:    { ios: 'home',         android: 'home' },
  search:  { ios: 'search',      android: 'search' },
  back:    { ios: 'chevron-back', android: 'arrow-back' },
  close:   { ios: 'close',       android: 'close' },
  share:   { ios: 'share-outline', android: 'share' },
  add:     { ios: 'add',         android: 'add' },
  delete:  { ios: 'trash-outline', android: 'delete-outline' },
} as const;

export function PlatformIcon({ name, size = 24, color }: PlatformIconProps) {
  const iconName = ICON_MAP[name]?.[Platform.OS] ?? name;
  const IconComponent = Platform.OS === 'ios' ? Ionicons : MaterialIcons;
  return <IconComponent name={iconName} size={size} color={color} />;
}

---

Phase 7: Dark Mode and Dynamic Color

Color System Adaptation

Token	iOS Light	iOS Dark	Android Light	Android Dark
Background	systemBackground (#FFFFFF)	systemBackground (#000000)	surface (#FFFBFE)	surface (#1C1B1F)
Surface	secondarySystemBackground (#F2F2F7)	secondarySystemBackground (#1C1C1E)	surfaceVariant (#E7E0EC)	surfaceVariant (#49454F)
Text Primary	label (#000000)	label (#FFFFFF)	onSurface (#1C1B1F)	onSurface (#E6E1E5)
Text Secondary	secondaryLabel (#3C3C43 @ 60%)	secondaryLabel (#EBEBF5 @ 60%)	onSurfaceVariant (#49454F)	onSurfaceVariant (#CAC4D0)
Primary	tintColor (app-defined)	tintColor (app-defined)	primary (Material You seed)	primary (Material You seed)
Destructive	systemRed (#FF3B30)	systemRed (#FF453A)	error (#B3261E)	error (#F2B8B5)
Separator	separator (#3C3C43 @ 30%)	separator (#545458 @ 65%)	outlineVariant (#CAC4D0)	outlineVariant (#49454F)

Android Material You Dynamic Color

Android 12+ extracts color from the user's wallpaper. Your app should respect it.

  User's Wallpaper        →    Extracted Palette    →    App Theme
  ┌──────────────┐            ┌─────────────────┐      ┌─────────────────┐
  │ ~~~~~~~~~~   │            │ Primary: #6750A4│      │ Buttons: #6750A4│
  │ ~~ 🌄 ~~~~   │  ────────▶ │ Secondary:#625B71│ ──▶ │ Cards:  #FFFBFE│
  │ ~~~~~~~~~~   │   extract  │ Tertiary: #7D5260│      │ FAB:    #6750A4│
  │ ~~~~~~~~~~   │            │ Neutral: #605D62│      │ Text:   #1C1B1F│
  └──────────────┘            └─────────────────┘      └─────────────────┘

Cross-Platform Color Abstraction

// shared/theme/colors.ts
import { Platform } from 'react-native';
import { DynamicColorIOS, PlatformColor } from 'react-native';

export const colors = {
  background: Platform.select({
    ios: PlatformColor('systemBackground'),
    android: PlatformColor('@android:color/background_light'),
    default: '#FFFFFF',
  }),
  text: Platform.select({
    ios: PlatformColor('label'),
    android: PlatformColor('@android:color/primary_text_light'),
    default: '#000000',
  }),
  separator: Platform.select({
    ios: PlatformColor('separator'),
    android: PlatformColor('@android:color/darker_gray'),
    default: '#C6C6C8',
  }),
};

---

Phase 8: Form Factor Adaptation

Device Matrix

Form Factor	iOS Devices	Android Devices	Layout Considerations
Phone (small)	iPhone SE (375pt)	360dp width devices	Single column, full-width cards
Phone (large)	iPhone 15 Pro Max (430pt)	412dp+ devices	Single column, slightly wider margins
Tablet	iPad (768pt+)	600dp+ tablets	Two-column master-detail, sidebar nav
Foldable (folded)	N/A	Galaxy Fold outer (280dp)	Compact single column
Foldable (unfolded)	N/A	Galaxy Fold inner (585dp)	Two-pane layout, avoid hinge
iPad Multitasking	Split View (50/50, 33/66)	N/A	Respond to size class changes

Responsive Layout Decision Tree

  Screen width in density-independent units?
  │
  ├─ < 380dp → COMPACT
  │   → Single column, stacked layout
  │   → Bottom sheet instead of side panel
  │   → Cards fill width with 16dp margins
  │
  ├─ 380-599dp → STANDARD PHONE
  │   → Single column, standard margins (16-20dp)
  │   → Bottom tabs (iOS) / bottom nav (Android)
  │   → Full-width content with card containers
  │
  ├─ 600-839dp → MEDIUM (small tablet / unfolded phone)
  │   → Two-column where appropriate
  │   → Navigation Rail (Android) / sidebar (iOS)
  │   → Master-detail split for list→detail flows
  │
  └─ 840dp+ → EXPANDED (tablet / desktop)
      → Multi-column layout
      → Permanent sidebar navigation
      → Master-detail is default pattern
      → Content max-width to prevent ultra-wide lines

Foldable Device Handling (Android)

  Folded State                         Unfolded State
  ┌─────────────┐                     ┌─────────────┬─────────────┐
  │             │                     │    Left     ││    Right    │
  │  Compact    │    ── unfold ──▶    │    Pane     ││    Pane     │
  │  Layout     │                     │  (list)    ││  (detail)   │
  │             │                     │             ││             │
  └─────────────┘                     └─────────────┴─────────────┘
                                                   ↑
                                                 hinge
                                            (avoid placing
                                            content here)

---

Platform-Specific File Organization

React Native — Recommended Structure

src/
├── components/
│   ├── Button.tsx                   ← shared component (no platform code)
│   ├── Header.tsx                   ← shared types + logic
│   ├── Header.ios.tsx               ← iOS-specific rendering
│   ├── Header.android.tsx           ← Android-specific rendering
│   └── PlatformIcon.tsx             ← platform-adaptive icon mapper
├── hooks/
│   ├── usePermissions.ts            ← shared permission interface
│   ├── usePermissions.ios.ts        ← iOS permission implementation
│   └── usePermissions.android.ts    ← Android permission implementation
├── utils/
│   ├── haptics.ts                   ← cross-platform haptic abstraction
│   ├── share.ts                     ← cross-platform share sheet
│   └── platform.ts                  ← Platform.select utilities
├── theme/
│   ├── tokens.ts                    ← shared design tokens
│   ├── colors.ios.ts                ← iOS system colors (PlatformColor)
│   └── colors.android.ts            ← Android system colors + dynamic
└── navigation/
    ├── AppNavigator.tsx             ← shared navigator structure
    ├── screenOptions.ios.ts         ← iOS nav options (large titles, swipe)
    └── screenOptions.android.ts     ← Android nav options (Material motion)

Flutter — Recommended Structure

lib/
├── widgets/
│   ├── adaptive_button.dart         ← CupertinoButton vs ElevatedButton
│   ├── adaptive_dialog.dart         ← CupertinoAlertDialog vs AlertDialog
│   ├── adaptive_scaffold.dart       ← CupertinoPageScaffold vs Scaffold
│   └── adaptive_switch.dart         ← CupertinoSwitch vs Switch
├── platform/
│   ├── permissions.dart             ← unified permission API
│   ├── haptics.dart                 ← HapticFeedback abstraction
│   └── share.dart                   ← share sheet abstraction
└── theme/
    ├── app_theme.dart               ← ThemeData + CupertinoThemeData
    ├── typography.dart              ← platform-aware text styles
    └── colors.dart                  ← adaptive color tokens

---

Common Adaptation Anti-Patterns

Anti-Pattern	Why It's Wrong	What to Do Instead
iOS-style bottom tabs on Android	Android uses Bottom Navigation (different height, shape, ripple)	Use platform-native navigation component
Android-style FAB on iOS	iOS has no FAB convention — users don't expect it	Use trailing nav bar button on iOS
Same alert dialog on both	iOS alerts look different from Material dialogs	Use CupertinoAlertDialog on iOS, AlertDialog on Android
Ignoring back gesture differences	iOS: swipe from left edge. Android: swipe from either edge	Configure platform-specific gesture handlers
Same switch component	UISwitch is wider and green. Material Switch is narrower and uses theme color	Use platform-native switch or adaptive wrapper
Hardcoded colors instead of system	Breaks dark mode, ignores dynamic color, ignores accessibility	Use PlatformColor, semantic tokens, or Material You
Same date picker on both	iOS uses wheel picker. Android uses calendar dialog	Use DateTimePicker with platform mode
Forcing custom fonts everywhere	Ignores system font benefits (Dynamic Type, font scaling)	Use system font as primary, custom for brand moments
Same scroll physics	iOS has rubber-band bounce. Android has stretch/glow overscroll	Let the platform provide default scroll physics
Ignoring Android edge-to-edge	Content hidden behind system bars	Apply WindowInsets correctly, draw behind system bars
Same keyboard avoidance	iOS: KeyboardAvoidingView. Android: windowSoftInputMode	Use platform-specific keyboard handling
Building custom permission dialogs	OS-mandated dialogs cannot be replaced	Show rationale BEFORE the system prompt, not instead of it

---

Tips for Best Results

1. Start with the differences matrix — before writing any code, identify which platform conventions apply to your feature. The matrix in Phase 1 is your checklist
2. Prototype on the harder platform first — if your feature involves gestures, start on Android (more gesture edge cases). If it involves system integration, start on iOS (stricter sandbox)
3. Use platform-specific files for complex differences — a 5-line Platform.select is fine. A 50-line branching block should be two separate files
4. Test on the cheapest Android device you can find — if it runs smooth on a budget phone, it runs smooth everywhere. Simulators lie about performance
5. Record your app and watch at 0.5x speed — you will catch every animation hitch, every layout jump, every incorrect gesture response
6. Read the actual platform guidelines every quarter — Apple and Google update HIG and Material Design regularly. What was correct last year might be deprecated now
7. Ship the same features to both platforms on the same day — platform parity prevents "why does Android get this but iOS doesn't?" support tickets
8. Keep your native module surface area as small as possible — every native module is a potential build failure on every framework upgrade
9. Respect system settings — dark mode, font scale, reduced motion, bold text. Users chose these settings for a reason. Override them and you lose their trust
10. Measure adaptation ROI — track which platform-specific adaptations actually improve retention or reduce support tickets. Cut the ones that don't matter