Mobile
90 bites tagged Mobile — interview questions with model answers, and 60-second explainers.
Instrumenting a New User Interaction in a Mobile App
Tests your understanding of the end-to-end analytics pipeline. A good answer defines the event, instruments it on the client with an SDK, verifies it in a debug view, and confirms its arrival in the data warehouse after the ETL process.
Handle Android Process Death vs. Configuration Changes
Tests your grasp of Android's lifecycle for state restoration. A good answer explains that `onCreate(savedInstanceState)` is called in both cases, but process death recreates everything. Use `ViewModel` with `SavedStateHandle`.
React Native's New Architecture Interop Layer
The Interop Layer is a compatibility bridge, letting legacy native modules run in React Native's New Architecture without a full rewrite. Library maintainers must ensure compatibility for users on RN 0.74+. The footgun: remove partial Codegen specs.
React Native Geolocation: The Web API on Mobile
Think of it as the web's `navigator.geolocation` API for your native app. Use it for map features or location-based content. The biggest footgun on iOS is forgetting location usage descriptions in `Info.plist`, which causes silent permission failures.
React Native NetInfo: Know Your Connection State
The NetInfo API is your app's network sensor, telling you if you're online and whether you're on WiFi or cellular. Use it to show an 'offline' banner or defer large downloads. The main footgun: `isConnected` only confirms a local link, not server reachability.
Bottom Tab Navigator: Core Mobile Navigation
A Bottom Tab Navigator is the classic mobile UI for switching between top-level app sections. It lazily loads screens, mounting them only when first focused to save memory. Use it for primary navigation.
Native Modules: Bridge JS to Native Platform APIs
Native Modules are your bridge from JavaScript to platform-specific APIs, letting your app use features not exposed by default. Use them when you need direct access to Android or iOS SDKs. The main footgun is misconfiguring Codegen in your project.
CI/CD for React Native: Automating App Releases
CI/CD for React Native is an assembly line for your app, taming the complexity of managing JS, Android, and iOS code. It automates builds on every push and deploys to stores. The main footgun is storing signing keys directly in your repo instead of using.
fastlane for React Native: Automating Native Builds
fastlane automates the native build and release steps for your React Native app. It scripts Xcode and Gradle tasks like code signing and uploading to stores, letting you ship from one command. The footgun: it only automates native toolchains, not JS bundling.
OTA Updates: Ship JS Fixes Without App Store Review
Over-the-Air (OTA) updates let you ship JavaScript, styling, and image changes directly to users, bypassing app store review. Use it to fix JS bugs or tweak UI between releases. The footgun: you can't update native code or change permissions this way.
Google Play Testing Tracks: A Funnel for Safer Releases
Google Play testing tracks act as a release funnel, moving from internal QA to public beta to catch bugs early. Use them for initial checks (Internal), private betas (Closed), or public tests on the Play Store (Open).
Google Play: The Android App Store
Google Play is the official digital storefront for the Android ecosystem. It's the primary channel where users on certified Android and ChromeOS devices discover and download apps. A common footgun is confusing the store with the developer-facing Play Console.
Detox: Gray-Box E2E Testing for React Native
Detox runs gray-box E2E tests by automatically synchronizing with your React Native app's activity. This eliminates flaky `sleep()` calls. Write one JavaScript test suite for iOS and Android that runs reliably on CI and real devices.
Turbo Modules: Type-Safe Native Code in React Native
Turbo Modules let your JS code call native APIs synchronously, skipping the slow async bridge. Use them to access device features or high-performance native libraries.
Flipper: A Desktop Debugger for React Native
Flipper is a desktop debugging platform for React Native, acting like Chrome DevTools for your mobile app. It connects to your local Metro server, letting you inspect component trees, view logs, and trigger reloads. The main footgun: the project is archived.
Local Notifications: Your App's On-Device Messenger
Local notifications are messages your app sends to itself on the user's device, no server needed. Use them for timers, reminders, or download progress. The footgun: forgetting to create Android Notification Channels will cause your alerts to fail silently.
React Native Push Notifications: Permissions First
Think of push notifications as your app's mailbox. Your server sends a message, but your React Native app must ask the user for permission to show it. This is key for sending alerts via Firebase, but on iOS, silent failures occur if you don't request.
Using Device Motion Sensors in React Native
Treat device sensors as a data stream. Instead of polling, subscribe to an observable that emits readings for acceleration or rotation. This is for building compasses, shake detection, or AR views.
React Native Camera Access: Permissions and Setup
Accessing the camera is a two-part contract: declare your intent in native config files, then ask the user for permission at runtime. This is required for any photo, video, or scanning feature.
React Native's Share API: Use the Native Share Sheet
The React Native Share API opens the native OS share sheet, letting users share content like URLs or text. It provides a familiar UI with a single cross-platform method call.
Handling Permissions in React Native
A unified permissions API gives you one way to request device features, avoiding separate logic for iOS and Android. It's essential for apps needing the camera or location. The main footgun is forgetting to configure the native project files.
withTiming: Animate Values Over a Set Duration
withTiming is your CSS transition for React Native animations. You define a target value, a duration, and an easing curve to create predictable, time-based animations like fades or size changes.
Animated: Drive Styles with Values, Not Setters
React Native's Animated API lets you drive styles with a value, not manual setters. Use it for performant fades and slides. The biggest footgun is forgetting `useNativeDriver: true`, which keeps animations smooth by running them off the JS thread.
Linking Native Dependencies in React Native
Installing a native library is a two-step process: fetch the JS code, then link the native iOS/Android parts. This is required for packages like `react-native-webview` that need native APIs. The footgun is forgetting to run `pod install` for iOS and rebuild.
Get Mobile bites daily.
Five a day, five minutes, offline. With quizzes so it sticks.
Open testing — you’ll join as an early tester.