Concepts in Mobile Dev, page 20
Vision Framework: Computer Vision on Apple Devices
The Vision framework is your on-device toolkit for understanding images and video. Use it for face detection, text recognition, or barcode scanning without needing ML expertise. Footgun: don't run requests on every frame; it drains the battery.
path_provider: Find Platform-Specific File Paths
path_provider asks the OS for standard file paths instead of you guessing. Use it to find the correct documents, temp, or cache directories on any platform. The footgun: not all paths exist on all systems, so always check for null returns.
React's useMemo Hook: Cache Expensive Calculations
useMemo is React's cache for expensive calculations, preventing re-computation on every render. Use it for heavy tasks like filtering large lists. The main footgun is an incomplete dependency array, which leads to stale, cached data.
StoreKit
StoreKit is Apple's framework for in-app purchases and subscriptions. It manages product lookup, presenting the payment sheet, processing transactions, and restoring purchases, so apps never touch raw payment data directly.
Reading and Writing Files in Dart
Treat files as either a single string for simple cases or a stream of data for large ones. Use dart:io for saving user settings or processing logs. The main footgun is using synchronous methods like readAsStringSync, which can freeze your app.
Analyzing Your React Native Bundle Size
Think of it as an X-ray for your app's final JavaScript file. It shows which libraries take up the most space, helping you shrink your app and improve startup time. The biggest mistake is only analyzing after performance degrades; do it proactively.
HealthKit: The Secure Vault for User Health Data
HealthKit is a secure, centralized database for user health data, not a sensor. Your app requests permission to read or write data like steps or workouts, which the OS manages. The footgun is assuming access; users grant permissions per data type.
sqflite: Local SQL Databases in Flutter
sqflite gives your Flutter app a private, on-device SQL database by wrapping the native SQLite engine. Use it for storing structured local data, like to-do lists or settings. The footgun: all database operations are async, so you must await every call.
Debugging React Native Performance
React Native drops frames when the JS thread overloads, not just from bad code. Complex re-renders, console.log statements, or dev mode freeze touches and animations. Never trust performance numbers from development builds; always test in release mode.
iOS Geofencing: Your App's Virtual Fence
Geofencing sets a virtual perimeter and lets iOS wake your app when a user enters or exits, without constant tracking. Use it for location-based reminders or context-aware features.
Hive: A Fast, Local Key-Value Store for Dart
Hive is a lightweight key-value database for Dart, acting like a persistent, super-fast Map. Use it to store simple data like user settings or cache API responses locally.
@HiltViewModel: Simplified ViewModel Injection
@HiltViewModel automates creating ViewModels with dependencies. Instead of writing custom factories, just annotate the ViewModel and its constructor. It's the standard for injecting dependencies like repositories into ViewModels in a Hilt-powered Android app.
Why-Did-You-Render: Find Unnecessary React Re-renders
The why-did-you-render library is a detective for your React app, finding components that re-render unnecessarily. Use it in development to debug performance by spotting when new object or function references break memoization.
ARKit: Building Augmented Reality on Apple Devices
ARKit is Apple's framework for blending digital objects with the real world using a device's camera. Use it for games, virtual furniture previews, or measurement tools.
flutter_secure_storage: Secure Key-Value Pairs
flutter_secure_storage is your go-to for saving sensitive data like API tokens. Think of it as an encrypted, cross-platform key-value store that uses native Keychain on iOS and strong ciphers on Android. The footgun: it's slower and meant only for secrets.
Inline Requires: Defer JS Loading in React Native
Inline requires are just-in-time loading for code. Instead of loading everything at startup, you pull in modules only when needed, improving initial app speed. This is ideal for heavy components. The footgun: module side effects will execute later.
Core Bluetooth: The Central vs. Peripheral Model
Core Bluetooth lets your app talk to BLE devices by acting as a "Central" (scanner) or "Peripheral" (advertiser). Use it to read from sensors or make your app discoverable.
Drift Schema Migrations: Evolving Your Database Safely
Think of schema migrations as a recipe for upgrading your app's database from an old version to a new one. You'll use them whenever you add a table or column in Drift. The footgun is forgetting to bump schemaVersion; your migration won't run.
Testing with Hilt: Swapping Dependencies for Isolation
Hilt testing swaps real app components for fakes, isolating your code under test without manual setup. It's used in UI and unit tests to replace production dependencies like network clients with test doubles.
Profiling React Native on Android with System Tracing
System Tracing helps you find UI jank on Android by showing where time is spent in each 16ms frame. Use it in Android Studio to diagnose stuttering animations by inspecting the UI, JS, and Native Module threads.
We are hiring for this. Every open role lists the topics its interview covers, so you can prepare for the real thing rather than guessing.
See open roles