Networking, storage, performance and publishing

Networking

• Android: Retrofit + OkHttp (+ kotlinx.serialization or Moshi). Flutter: http or Dio. React Native: fetch/axios with TanStack Query.
• Always handle loading, success, empty and error states; show retry options; set timeouts.
• Offline-first: render from the local cache immediately, refresh in the background, queue writes made offline and sync later.
• Pagination for long lists; images through a caching library (Coil, Glide, cached_network_image, FastImage).

Local storage

• Key-value settings: DataStore / SharedPreferences (Android), shared_preferences (Flutter), AsyncStorage/MMKV (RN).
• Structured data: Room (Android), Drift/sqflite/Isar (Flutter), SQLite/WatermelonDB (RN).
• Secrets and tokens: Android Keystore / EncryptedSharedPreferences, iOS Keychain, flutter_secure_storage. Never plain preferences.

Firebase (very common in Indian startups)

Authentication (phone OTP), Firestore (real-time NoSQL database), Cloud Messaging (push notifications), Crashlytics (crash reports), Analytics, Remote Config (feature flags) and App Distribution (test builds).

Performance on budget phones

• Keep the main/UI thread free: heavy work on background threads, coroutines or isolates.
• Lists: lazy/virtualised lists with stable keys; avoid deep nested layouts.
• Images: right-sized, compressed, cached.
• Startup time: defer non-critical initialisation; measure cold start.
• App size: shrink with R8/ProGuard, Android App Bundles, remove unused assets and libraries.
• Battery: batch network calls, avoid frequent wake-ups, use WorkManager constraints.
• Profile with Android Studio Profiler, Flutter DevTools or Flipper/React DevTools.

Security basics

HTTPS only (consider certificate pinning for sensitive apps), no secrets hard-coded in the app (they can be extracted), obfuscation, root/jailbreak checks for banking-grade apps, and validation on the server, not just in the app.

Testing and release

• Unit tests for ViewModels/business logic; UI tests (Espresso, Compose testing, Flutter widget tests, Detox) for key flows.
• CI builds signed releases (Fastlane, Codemagic, GitHub Actions, EAS for Expo).
• Play Store: signed App Bundle, store listing, privacy policy and data safety form, content rating; internal → closed → open testing tracks; staged rollout (5% → 20% → 100%) while watching crash-free rate.
• Force-update or soft-update prompts to retire old versions; backend APIs versioned so old apps keep working.

Portfolio tip

Publish one real, small app on the Play Store (or as an APK with a demo video): a clean architecture, offline support, and a README explaining decisions. It beats five tutorial clones.

Check yourself

• How would you make a job-listing screen work offline?
• Where should an auth token be stored on Android?
• What is a staged rollout and why use it?