iOS Developer Interview Prep Guide

Cover how actors prevent data races at compile time, how TaskGroups manage concurrent work with automatic cancellation, and how structured concurrency ties task lifetime to scope. GCD is still useful for precise queue management, interop with C APIs, and performance-critical dispatch to specific QoS classes.

Discuss NavigationStack with NavigationPath for programmatic navigation, a coordinator pattern adapted for SwiftUI, and state restoration via Codable navigation state persisted to disk. Address the challenges of deep linking into nested navigation hierarchies and handling authentication gates.

Explain strong, weak, and unowned references, capture lists in closures, and how the Memory Graph Debugger and Instruments Allocations tool help find leaks. Provide a concrete example of a retain cycle between a view controller, its closure-based network callback, and how adding [weak self] resolves it.

Enable Address Sanitizer and Thread Sanitizer to reproduce locally. Check for race conditions accessing shared mutable state without synchronization. Review recent changes involving background work. Use the crash log symbolication to identify the exact frame and work backward through the call stack.

Use protocol-oriented design with an Endpoint protocol defining path, method, headers, and body. Leverage async/await for clean call sites, generic Decodable response handling, and a token refresh interceptor that queues concurrent requests during refresh. Show error handling with typed errors.

Discuss declarative vs imperative paradigms, SwiftUI state management (@State, @ObservedObject, @EnvironmentObject), interop via UIHostingController and UIViewRepresentable. For decision criteria, consider team expertise, feature complexity, minimum iOS version, and whether the feature benefits from SwiftUI previews for rapid iteration.

Describe an incremental approach: bridging header setup, starting with model and utility layers, module-by-module migration with interop testing, and how you maintained backwards compatibility. Mention specific challenges like nullability annotations, NS_SWIFT_NAME macros, and testing both languages in CI.

Use CADisplayLink with preferredFrameRateRange to adapt to ProMotion. Implement the animation with Core Animation or Metal for GPU-accelerated rendering. Discuss how to avoid main thread blocking, use time-based animation rather than frame-based, and reduce frame rate when animation is not visible.