Mobile Design

                    UNIFY (same on both)          DIVERGE (platform-specific)
                    ───────────────────           ──────────────────────────
Business Logic      ✅ Always                     -
Data Layer          ✅ Always                     -
Core Features       ✅ Always                     -
                    
Navigation          -                             ✅ iOS: edge swipe, Android: back button
Gestures            -                             ✅ Platform-native feel
Icons               -                             ✅ SF Symbols vs Material Icons
Date Pickers        -                             ✅ Native pickers feel right
Modals/Sheets       -                             ✅ iOS: bottom sheet vs Android: dialog
Typography          -                             ✅ SF Pro vs Roboto (or custom)
Error Dialogs       -                             ✅ Platform conventions for alerts

Desktop: Cursor is precise (1px)
Mobile:  Finger is imprecise (~7mm contact area)

→ Touch targets MUST be 44-48px minimum
→ Important actions in THUMB ZONE (bottom of screen)
→ Destructive actions AWAY from easy reach

┌─────────────────────────────┐
│      HARD TO REACH          │ ← Navigation, menu, back
│        (stretch)            │
├─────────────────────────────┤
│      OK TO REACH            │ ← Secondary actions
│       (natural)             │
├─────────────────────────────┤
│      EASY TO REACH          │ ← PRIMARY CTAs, tab bar
│    (thumb's natural arc)    │ ← Main content interaction
└─────────────────────────────┘
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// ✅ CORRECT: Memoized renderItem + React.memo wrapper
const ListItem = React.memo(({ item }: { item: Item }) => (
  <View style={styles.item}>
    <Text>{item.title}</Text>
  </View>
));

const renderItem = useCallback(
  ({ item }: { item: Item }) => <ListItem item={item} />,
  []
);

// ✅ CORRECT: FlatList with all optimizations
<FlatList
  data={items}
  renderItem={renderItem}
  keyExtractor={(item) => item.id}  // Stable ID, NOT index
  getItemLayout={(data, index) => ({
    length: ITEM_HEIGHT,
    offset: ITEM_HEIGHT * index,
    index,
  })}
  removeClippedSubviews={true}
  maxToRenderPerBatch={10}
  windowSize={5}
/>

// ✅ CORRECT: const constructors prevent rebuilds
class MyWidget extends StatelessWidget {
  const MyWidget({super.key}); // CONST!

  @override
  Widget build(BuildContext context) {
    return const Column( // CONST!
      children: [
        Text('Static content'),
        MyConstantWidget(),
      ],
    );
  }
}

// ✅ CORRECT: Targeted state with ValueListenableBuilder
ValueListenableBuilder<int>(
  valueListenable: counter,
  builder: (context, value, child) => Text('$value'),
  child: const ExpensiveWidget(), // Won't rebuild!
)

GPU-accelerated (FAST):     CPU-bound (SLOW):
├── transform               ├── width, height
├── opacity                 ├── top, left, right, bottom
└── (use these ONLY)        ├── margin, padding
                            └── (AVOID animating these)

🧠 CHECKPOINT:

Platform:   [ iOS / Android / Both ]
Framework:  [ React Native / Flutter / SwiftUI / Kotlin ]
Files Read: [ List the skill files you've read ]

3 Principles I Will Apply:
1. _______________
2. _______________
3. _______________

Anti-Patterns I Will Avoid:
1. _______________
2. _______________

🧠 CHECKPOINT:

Platform:   iOS + Android (Cross-platform)
Framework:  React Native + Expo
Files Read: touch-psychology.md, mobile-performance.md, platform-ios.md, platform-android.md

3 Principles I Will Apply:
1. FlatList with React.memo + useCallback for all lists
2. 48px touch targets, thumb zone for primary CTAs
3. Platform-specific navigation (edge swipe iOS, back button Android)

Anti-Patterns I Will Avoid:
1. ScrollView for lists → FlatList
2. Inline renderItem → Memoized
3. AsyncStorage for tokens → SecureStore

WHAT ARE YOU BUILDING?
        │
        ├── Need OTA updates + rapid iteration + web team
        │   └── ✅ React Native + Expo
        │
        ├── Need pixel-perfect custom UI + performance critical
        │   └── ✅ Flutter
        │
        ├── Deep native features + single platform focus
        │   ├── iOS only → SwiftUI
        │   └── Android only → Kotlin + Jetpack Compose
        │
        ├── Existing RN codebase + new features
        │   └── ✅ React Native (bare workflow)
        │
        └── Enterprise + existing Flutter codebase
            └── ✅ Flutter