Mobile Development

Mobile Development

Mobile apps run on devices you don't control. Design for offline, memory constraints, and slow networks from the start.

UI and Navigation

• Use a declarative navigation library (React Navigation, Go Router) rather than imperative stack manipulation. Navigation state should be serializable for deep linking.
• Support deep links and universal links from day one — retrofitting them is painful. Map every screen to a URL.
• Design for safe areas: iOS notch, Android status bar, and home indicator eat into usable screen space. Use SafeAreaView / SafeAreaProvider or equivalent.
• Support both orientations unless the app's UX is genuinely portrait-only. Locking to portrait breaks tablets and landscape-preferred users.
• Keep gestures consistent with platform conventions: back gesture on Android, swipe-to-go-back on iOS. Don't fight the platform.

Performance

• Avoid rendering inside onScroll handlers — debounce or use virtualized list components (FlatList, LazyColumn) that recycle cells.
• Move heavy computation (image processing, JSON parsing of large payloads) off the JS/Dart thread using native modules or isolates.
• Profile with platform tools: Xcode Instruments (iOS) and Android Studio Profiler. Wall-clock time in a dev build is not representative of release.
• Target 60fps (16ms per frame) for scroll and animation. 120fps on ProMotion displays requires explicit opt-in.
• Defer non-critical work using InteractionManager.runAfterInteractions (RN) or WidgetsBinding.instance.addPostFrameCallback (Flutter).

Network and Offline

• Assume the network is unavailable at any point. Cache critical data locally (SQLite, Hive, MMKV) and sync opportunistically.
• Implement optimistic UI updates for user actions: show the result immediately, roll back on error.
• Use exponential backoff with jitter for network retries. Never retry in a tight loop.
• Show meaningful offline states — empty screens with "no connection" are better than spinner-forever states.
• Handle background app refresh carefully: iOS background fetch is time-limited and may be denied. Design sync to resume from where it stopped.

Platform Permissions

• Request permissions just-in-time, immediately before the first use. Never request permissions on app launch.
• Handle all three states: granted, denied, and denied-permanently. Show rationale UI before the OS prompt.
• For sensitive permissions (location, microphone, camera), explain the specific use case in the rationale. "App needs location" is not a rationale.
• Test permission flows in a clean install state — cached permission state in development hides cold-start bugs.

App Size and Build

• Analyze the bundle with react-native-bundle-visualizer (RN) or --analyze (Flutter). Find and remove unused dependencies.
• Enable Hermes (RN) and AOT compilation (Flutter release mode) — they significantly reduce startup time.
• Split assets into multiple APK/AAB splits by ABI or use --split-per-abi to avoid shipping arm64 bytecode to armv7 devices.
• Test release builds before submission — dev builds have different performance characteristics, JS source maps, and debug settings.

Checklist

• Deep linking configured for all main screens.
• Safe area insets handled on all platforms.
• Virtualized lists used for any list > 50 items.
• Offline state handled gracefully with local cache.
• Permissions requested just-in-time with rationale UI.
• Release build tested on a physical device before submission.
• App bundle analyzed for unused dependencies.