More in Mobile Dev — page 16
React Native Gesture Handler: Native-Driven Touch
React Native Gesture Handler moves touch recognition to the native thread so gestures stay smooth when JavaScript is busy. Use it for swipeable cards and bottom sheets. The footgun is using it without Reanimated, gaining complexity without the frame-rate win.
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.
Adaptive React Native UIs for Tablets and Foldables
Adaptive UI is context-aware layout, not just stretching pixels. It matters when a phone app hits a tablet or a foldable unfolds. Most devs stop at flexbox and wonder why the tablet experience still feels like a blown-up phone.
React Native's Platform Build Glue
React Native integrates into Android via Gradle files. You edit settings.gradle and both build.gradle files to wire the React Native Gradle Plugin and enable autolinking. The footgun: editing the wrong build.gradle breaks native modules silently.
Touchable Components in React Native
TouchableOpacity and siblings wrap views to give press feedback by dimming or highlighting. Use them for simple taps on buttons or list items. They inject extra Animated.View nodes that can silently break layout, and Pressable has superseded the entire family.
Describe lightweight vs heavyweight Core Data migration and a heavyweight example
This tests inferred versus manual Core Data migrations. Contrast lightweight additive changes with heavyweight transforms like entity splits, citing promoting a string to a new entity. A red flag is claiming renames always need custom mapping.
Describe a pattern for background Core Data fetches and UI updates
This tests NSManagedObjectContext concurrency and queue confinement. Strong answer: create a background context, fetch, pass objectIDs or structs to main, then main context fetches by ID to update UI. Red flag: passing NSManagedObjects across threads.
How do you persist a custom Swift struct to JSON in Documents?
Tests fluency with Codable and FileManager sandbox APIs. Good answer: conform to Codable, encode with JSONEncoder, resolve Documents directory via FileManager URLs, write Data atomically, and reverse with JSONDecoder.
When is UserDefaults right, what are its limits, and native types?
Tests if you treat UserDefaults as a small preference store, not a database. Good answers name native plist types, cite no encryption and small size limits, and name Core Data or Keychain for heavy or sensitive data. Red flag: storing images or passwords.
Design state-driven navigation for a conditional wizard in UIKit and SwiftUI
This tests separating navigation state from UI. Model the flow as a state machine enum, derive the stack from state, and unit test transitions in plain Swift. A red flag is imperative pushes inside views or view controllers.
How would you architect the app root for onboarding vs authenticated flows?
Tests window root swapping and state-driven architecture. Use a coordinator to own the window, swap rootViewController between nav and tab controllers on auth changes, and crossfade. Red flag: onboarding modal over tabs or keeping both hierarchies alive.
What NavigationView limitations did NavigationStack solve for programmatic navigation?
This tests why NavigationView programmatic navigation was brittle. A strong answer contrasts scattered NavigationLink isActive booleans and broken multi-destination stacks against NavigationStack's unified path array. A red flag is calling it a simple rename.
How do you pop to root in SwiftUI NavigationStack?
This tests declarative state-driven navigation. A strong answer binds NavigationStack to a NavigationPath, passes the binding down, and clears the path to pop to root. A red flag is suggesting UIKit popToRootViewController or legacy isActive hacks.
Handle a deep link URL in SceneDelegate and navigate to order detail.
WHAT IT TESTS: iOS scene-based deep links. ANSWER: Handles willConnectTo and openURLContexts; parses path with URLComponents; validates ID; pushes detail onto nav stack. RED FLAG: Forgetting warm launches or routing without checking view hierarchy.
Pass data back from a modally presented view controller delegate versus closure
This tests decoupled UIKit communication and memory safety. A strong answer outlines a weak delegate protocol and a closure with weak self, contrasting coupling and retain cycles. Red flag: singletons or direct parent references.
Explain the Coordinator pattern and the navigation problem it solves in MVC
This tests if you see view controllers bloat from absorbing navigation flow. A good answer names 3 problems (delegate bloat, massive view controllers, embedded routing) and says coordinators own creation and routing.
Implement SwiftUI navigation between list and detail with product ID
Tests modern SwiftUI navigation and clean data flow. Great answer: NavigationStack with NavigationLink(value:) and navigationDestination(for:), plus a bound path for programmatic control.
Outline the key steps and APIs for State Preservation and Restoration
Tests UIKit's automatic state restoration pipeline. Strong answers cover: opting in via AppDelegate, setting restorationIdentifiers, implementing encode/decodeRestorableStateWithCoder, and the system snapshot cycle.
How does the Coordinator pattern decouple navigation, and what are its components?
This tests iOS separation of concerns. Explain that Coordinators extract navigation logic from view controllers for reuse, and describe AppCoordinator tree with child coordinators. A red flag is treating it as a router or ignoring parent-child retention.
How do you complete a file download after the app backgrounds?
This tests iOS background execution and URLSession background transfers. Configure a background URLSession, handle AppDelegate events, and respect the 30-second completion handler limit. Never claim NSTimer or beginBackgroundTask sustains background downloads.