Objective-C Interview Questions 2025

This article concerns real-time and knowledgeable Objective-C Interview Questions 2025. It is drafted with the interview theme in mind to provide maximum support for your interview. Go through these Objective-C interview Questions to the end, as all scenarios have their importance and learning potential.

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These solutions are based on my experience and best effort. Actual results may vary depending on your setup. Codes may need some tweaking.

1. What makes Objective-C still relevant in iOS projects despite Swift’s rise?

Many enterprises have revenue-critical apps written in Objective-C, so stability beats a risky rewrite.
It interops cleanly with C/C++ libraries that power performance-heavy modules.
Mature SDKs and internal frameworks often expose Objective-C APIs first.
Teams benefit from predictable runtime behavior built over years.
Hiring for maintenance and incremental change is cheaper than full migration.
Knowledge of Objective-C helps debug legacy crashes faster.
Mixed-language setups keep feature velocity high without breaking old code.

2. How do teams practically manage mixed Objective-C + Swift codebases?

Use a clear boundary: legacy modules in Objective-C, new features in Swift.
Keep a dedicated bridging header and limit what you expose across it.
Enforce naming and nullability annotations so Swift callers stay safe.
Write tests around the seams so refactors don’t regress behavior.
Centralize models/protocols to minimize duplicated types.
Agree code-style rules so reviews don’t get stuck on syntax.
Document ownership of legacy areas to reduce accidental breakage.

3. What common pitfalls appear when onboarding to an Objective-C legacy app?

Confusing memory rules around strong/weak/unsafe_unretained references.
Hidden retain cycles in delegates, timers, and blocks.
Overuse of categories that hide where logic truly lives.
Runtime gymnastics (swizzling, message forwarding) that surprise newcomers.
Sparse unit tests around the oldest modules.
Outdated third-party pods with no Swift equivalents.
Mixed ARC/MRC files that need careful reviews.

4. Where does Objective-C’s dynamic runtime help, and where does it hurt?

It helps with plugin-style designs, mocking, and late binding of behaviors.
Framework authors can intercept selectors for cross-cutting concerns.
But swizzling can create spooky, non-local effects that break later.
Debugging message forwarding chains is time-consuming for juniors.
Performance can dip if you lean too hard on dynamism.
Teams often restrict swizzling to a tiny, well-audited layer.
Clear comments and tests are mandatory when touching the runtime.

5. When would you recommend keeping a module in Objective-C instead of porting?

It’s stable, revenue-critical, and rarely changes.
It depends on C/C++ libraries or Core Foundation lifetimes.
The team lacks bandwidth to rewrite and re-validate edge cases.
The code is wrapped behind clean protocols already.
There are no Swift-only language features that truly help here.
Performance is proven and instrumentation shows no hotspots.
A port would add risk without measurable business value.

6. How do categories and class extensions improve large Objective-C codebases?

Categories add focused methods without subclassing or bloating classes.
You can split giant files by domain, improving navigation.
Private extensions hide internals while keeping headers clean.
They support progressive refactoring toward smaller responsibilities.
They reduce merge conflicts by isolating new behaviors.
Teams can prototype safely without touching core logic.
With naming discipline, they keep readability high.

7. What’s your stance on method swizzling in production apps?

It’s a sharp tool: reserve for tiny, justified patches only.
Prefer documented extension points before reaching for swizzling.
Guard with version checks and unit tests to catch SDK changes.
Keep it centralized so auditors know where it lives.
Log when swizzled methods run to aid debugging.
Avoid swizzling in frequently called hot paths.
Always document the undo/rollback plan.

8. How do you prevent retain cycles with blocks in Objective-C?

Default to __weak self inside blocks that outlive the scope.
If self must be strong, upgrade temporarily inside the block.
Watch out for blocks stored on properties or queues.
Be extra careful with view controllers capturing UI elements.
Add Instruments’ Leaks/Allocations to your PR checklist.
Write small block bodies to spot captures at a glance.
Prefer explicit parameters over capturing broad context.

9. What are the practical differences between `assign`, `weak`, and `strong`?

strong keeps the object alive for your property’s lifetime.
weak avoids retain cycles and auto-nil’s when targets deallocate.
assign is for primitives; using it on objects risks dangling pointers.
Use weak for delegates and parent references.
Use strong for owned collaborators and models.
Avoid unsafe_unretained unless bridging to legacy patterns.
Match attribute choice with real ownership decisions.

10. When do you choose `copy` for Objective-C properties?

For NSString, to protect against mutable subclass surprises.
For blocks, so you capture them to the heap safely.
For collections you want to keep immutable by contract.
It clarifies the API: callers can’t mutate your internal state.
Slight memory overhead is worth the predictability.
Use copy selectively and measure if on hot paths.
Document why copy matters in that specific property.

11. How do you approach ARC mixed with Core Foundation types?

Remember ARC doesn’t manage CF objects automatically.
Use bridging casts like __bridge_transfer when transferring ownership.
Pair creates/copies with corresponding releases on CF types.
Wrap CF lifetimes behind small Objective-C helpers.
Add unit tests to prove no leaks or over-releases.
Profile with Instruments to verify assumptions.
Avoid scattering CF calls across random classes.

12. What’s your strategy for NSNotificationCenter safety?

Always remove observers in dealloc or on lifecycle events.
Prefer block-based tokens and store them for clean removal.
Keep notification names centralized to avoid typos.
Avoid passing huge userInfo payloads; define lean contracts.
Don’t treat notifications as a primary architecture.
Use them for decoupled events, not for critical flows.
Test that observers don’t outlive their owners.

13. How do you decide between delegation, notifications, and blocks?

Delegation fits one-to-one, stateful conversations.
Notifications fit one-to-many broadcast updates.
Blocks fit inline callbacks where you don’t need a long-lived delegate.
Pick the simplest pattern that communicates intent clearly.
Don’t mix patterns for the same relationship.
Consider testability and memory risks before choosing.
Document the chosen pattern in the module README.

14. What’s your view on singletons in Objective-C?

Useful for shared, stateless services like logging or configuration.
Create them with dispatch_once to avoid race conditions.
Keep them small and focused; avoid business logic inside.
Don’t hide global state behind a singleton.
Test them with dependency injection, not hard-coded access.
Watch for retain cycles if they hold long-lived objects.
Consider module-scoped factories as alternatives.

15. How do you make Objective-C APIs friendlier to Swift?

Add nullability annotations to every public header.
Use lightweight generics on collections for type safety.
Prefer modern NS types and avoid id-heavy signatures.
Use NS_SWIFT_NAME to improve call-site clarity.
Return NSError** instead of magic return codes.
Keep ObjC names concise so Swift doesn’t get verbose.
Provide small adapters if the Swift side needs value types.

16. What risks appear when refactoring long Objective-C view controllers?

Accidentally breaking delegate/datasource connections.
Hidden logic in categories that you forget to move.
Retain cycles introduced by new blocks or timers.
Tight coupling to storyboards or nibs complicating tests.
Side effects in viewWillAppear that should be elsewhere.
Fix by extracting presenters or coordinators incrementally.
Guard each step with snapshot and unit tests.

17. How do you structure error handling with `NSError**` cleanly?

Return BOOL and fill an NSError** for failure details.
Define error domains and codes in one shared header.
Provide human-readable NSLocalizedDescriptionKey.
Avoid piling multiple root causes into one error.
Don’t swallow errors; log with context once.
Convert to Swift throw at the bridging boundary.
Test with both expected and malformed inputs.

18. What’s the practical use of `NSOperation` vs GCD today?

GCD is lightweight for simple async tasks and queues.
NSOperation adds cancellation, dependencies, and KVO.
Use operations for complex workflows that need control.
Keep GCD for quick background tasks and UI hops.
Avoid mixing the two in the same flow without reason.
Name queues clearly to aid crash logs and debugging.
Build small, reusable operation subclasses when needed.

19. How do you approach thread safety in Objective-C models?

Treat models as immutable where possible.
Use serial queues or locks around mutable state.
Keep state changes centralized behind small APIs.
Avoid exposing raw mutable collections.
Prefer copy-on-write semantics for performance.
Test with stress tools and randomized access.
Document threading guarantees in headers.

20. What’s your checklist for avoiding timer-related memory leaks?

Use weak references to self when timers fire.
Invalidate timers on viewWillDisappear or deinit paths.
Prefer block-based timers with captured weak owners.
Avoid repeating timers when a one-shot works.
Don’t keep timers alive in background unnecessarily.
Store timers in a dedicated owner to centralize cleanup.
Add unit tests that simulate lifecycle transitions.

21. How do you keep massive headers from leaking internals?

Use class extensions for private properties and ivars.
Forward declare classes instead of importing whole headers.
Expose only what callers truly need.
Group headers by module and responsibility.
Consider umbrella headers for public APIs.
Keep comments short but precise about contracts.
Run include-what-you-use checks in CI.

22. What’s your approach to memory spikes from autorelease pools?

Drain pools in tight loops with @autoreleasepool blocks.
Don’t allocate large temporary objects inside hot paths.
Reuse buffers or caches when safe.
Validate with Allocations and Heap Shot tools.
Split work into chunks to reduce peak memory.
Watch for hidden autoreleases from convenience APIs.
Log memory warnings with diagnostic breadcrumbs.

23. How do you decide between `id` and generics on collections?

Prefer generics for compile-time safety in public APIs.
Use id for truly polymorphic, dynamic cases.
Adding generics improves Swift interop immediately.
Don’t over-genericize where it adds noise.
Keep type aliases to simplify complex signatures.
Update tests to catch accidental type regressions.
Document any id uses with expected types.

24. What patterns help test Objective-C code without heavy refactors?

Program to protocols so you can inject fakes.
Wrap singletons in small provider interfaces.
Use dependency injection instead of hard global access.
Keep side effects behind command objects or services.
Make constructors take collaborators explicitly.
Favor composition over subclassing for behavior.
Write thin adapters for external SDKs.

25. How do you safely adopt modern APIs in an older Objective-C app?

Gate with availability checks and fallbacks.
Keep adapters that isolate SDK differences by OS version.
Write targeted A/B tests for critical code paths.
Roll out behind feature flags if user-facing.
Update deployment targets only with stakeholder buy-in.
Document new minimum OS and test matrices.
Monitor crash analytics after release.

26. What’s your playbook for reducing massive `.m` files?

Identify cohesive groups and extract to categories.
Move business rules to service classes or presenters.
Keep view controllers focused on view orchestration.
Split by feature slices rather than layers when helpful.
Add unit tests before moving risky logic.
Leave shims that log if the old entry points are called.
Update README with new file map.

27. How do you manage deprecations in Objective-C code over time?

Mark old APIs with DEPRECATED_MSG_ATTRIBUTE macros.
Provide migration notes and examples in headers.
Keep compatibility shims until adoption crosses a threshold.
Track usage via grep or static analysis in CI.
Remove dead APIs on a planned release train.
Communicate timelines early with all teams.
Celebrate deletions to reinforce cleanup culture.

28. What mistakes cause flaky KVO setups in Objective-C?

Forgetting to remove observers on deallocation.
Observing wrong key paths or misspelled constants.
Doing heavy work inside KVO callbacks on main thread.
Not guarding against nil or unexpected types.
Relying on KVO for business logic instead of UI sync.
Using KVO when delegation or blocks would be clearer.
Tests should verify add/remove symmetry.

29. How do you approach localization and string safety in Objective-C?

Centralize keys and avoid inline literals scattered around.
Use format specifiers carefully to avoid crashes.
Provide context comments for translators.
Validate pluralization and gender rules where needed.
Test pseudolocalization and long strings in UI.
Keep fallback language consistent and complete.
Track missing keys with runtime assertions in debug.

30. What practical steps improve Objective-C app launch time?

Defer heavy work out of +load and +initialize.
Delay non-critical service setup until after first paint.
Cache computed values that are stable per session.
Reduce dynamic swizzling that runs at startup.
Trim large nib/storyboard loads when possible.
Prewarm critical caches on the first idle run loop.
Measure each change with Instruments to confirm gains.

31. How do you keep Core Data usage safe in Objective-C?

Use private queue contexts and merge on main carefully.
Keep managed objects off background threads unless pinned.
Normalize large imports into batches with autorelease pools.
Don’t leak contexts; tie them to clear owners.
Map errors to user-meaningful messages, not codes.
Back migrations with reliable backups and tests.
Profile fetch requests for indexes and predicates.

32. What’s your advice on bridging Swift value types into Objective-C?

Wrap Swift structs behind Objective-C classes if needed.
Limit surface area to Objective-C-friendly types.
Convert at the boundary and keep internals in Swift.
Avoid forcing ObjC to understand complex generics.
Use typed initializers to prevent misuse.
Document performance implications of conversions.
Test serialization both ways to avoid data loss.

33. How do you approach performance tuning before optimizing Objective-C code?

Reproduce with a small, reliable benchmark first.
Use Instruments to find the real hotspots, not guesses.
Optimize allocations and string work on hot paths.
Cache results only when measurements justify it.
Prefer algorithmic fixes over micro-optimizations.
Keep changes small and compare before/after numbers.
Add regression tests to guard performance.

34. What guardrails help when using `performSelector:` APIs?

Prefer compile-time safety with direct method calls when possible.
If dynamic, centralize selectors and test them explicitly.
Validate target/action existence before sending messages.
Avoid passing ARC-unaware pointers across boundaries.
Keep selectors private if they’re implementation details.
Use pragma diagnostic pushes to highlight risky spots.
Consider blocks or protocols for clarity.

35. How do you reason about `+load` vs `+initialize` in classes?

+load runs at load time; keep it minimal to avoid startup cost.
+initialize is lazy and runs before first message; prefer it.
Never rely on ordering between multiple +loads.
Use them for wiring tiny, safe defaults only.
Avoid side effects that depend on other modules.
Document why static work can’t be deferred later.
Measure if changes shift cold-start time.

36. What patterns reduce UIKit-on-background-thread bugs in ObjC apps?

Treat UIKit as main-thread-only by default.
Hop to main for any view or layer update.
Use dispatch_assert_queue checks in debug utilities.
Wrap async responses to deliver on the main queue.
Keep background work pure data and parsing.
Write tests that detect off-main usage in CI.
Log violations during development builds.

37. How do you avoid overusing macros in Objective-C?

Prefer inline functions and constants for type safety.
Keep macros for logging and compile-time flags only.
Don’t hide control flow or complex logic in macros.
Names should scream intent and avoid collisions.
Document any macro that touches arguments multiple times.
Replace legacy macros with enums and static inlines.
Review macro usage regularly for maintainability.

38. What’s a clean way to organize feature flags in an ObjC app?

Centralize flags in a small, typed provider.
Fetch remote config early but activate gradually.
Keep flags short-lived; prune after rollout.
Avoid sprinkling if (flag) everywhere; encapsulate behavior.
Log flag states in diagnostics for bug reports.
Test both paths in unit tests to avoid rot.
Document owner and expiry date per flag.

39. How do you keep app analytics from polluting Objective-C business logic?

Wrap analytics behind a protocol with no SDK leakage.
Inject the tracker so tests can pass a no-op.
Keep event names and params centralized and typed.
Batch sends off the main thread to avoid jank.
Version events so schema updates don’t break dashboards.
Validate PII rules and keep payloads minimal.
Review events with product before shipping.

40. How do you approach migrating storyboards in a legacy Objective-C app?

Move incrementally: new flows use XIBs or programmatic UI.
Keep the old storyboard until features are parity.
Extract view controllers into smaller presenters first.
Add snapshot tests to freeze visual expectations.
Avoid changing navigation structure mid-migration.
Track crash rates and UI feedback closely after releases.
Delete old artifacts once funnels are stable.

41. What practical limits do you set for category methods?

Never override methods from the original class.
Keep names prefixed to avoid collisions.
Scope categories to one responsibility each.
Don’t expose categories as your public API surface.
Use them mainly for internal helpers or shims.
Document any performance-sensitive category work.
Prefer extensions if you control the class source.

42. How do you ensure safe use of `mutableCopy` and collection mutations?

Treat copies as new ownership; don’t leak references.
Convert mutable collections back to immutable when returning.
Avoid exposing mutable collections over public APIs.
Use defensive copies in initializers if callers pass mutables.
Keep mutation localized to one method to aid reasoning.
Add tests that assert immutability contracts.
Profile large copies and prefer in-place edits if safe.

43. What’s your checklist for safe URL loading in Objective-C?

Validate URLs and schemes before creating requests.
Use background sessions for large or long-running transfers.
Keep timeouts and retries explicit, not default.
Map errors to user actions that make sense.
Avoid work on main during response parsing.
Log request IDs to correlate with server traces.
Secure headers and tokens; never print secrets.

44. How do you protect against crashy selector mismatches at runtime?

Prefer protocols to guarantee method presence.
Use respondsToSelector: checks when dealing with optional methods.
Keep selectors in constants to avoid typos.
Avoid dynamic strings to build selectors.
Add unit tests for optional delegate paths.
Fail fast in debug with assertions when contracts break.
Document optional vs required behaviors clearly.

45. How do you keep objective-c models future-proof with API changes?

Build with resilience: ignore unknown fields when parsing.
Keep server-driven feature flags and versioning.
Validate required vs optional properties strictly.
Provide migrations for stored models when schemas change.
Log parsing anomalies to detect silent breaks.
Keep adapters that isolate API quirks from the app.
Add contract tests with sample payloads.

46. What strategies reduce crash risk during SDK upgrades in ObjC apps?

Upgrade in small steps and read change logs carefully.
Wrap SDK calls behind your interface for easy rollback.
Create a test build that hits high-risk screens first.
Monitor crash groups by SDK version in analytics.
Keep precise reproduction notes for vendor support.
Don’t mix multiple SDK upgrades in one release.
Gate new SDK features behind flags.

47. How do you reason about `weak` references turning nil unexpectedly?

Accept that weak is about avoiding cycles, not ownership.
Re-strongify locally when you actually use the object.
Guard critical paths with early returns if it’s nil.
Don’t store weak references you rely on for business logic.
Favor explicit lifetimes with strong where needed.
Tests should simulate deallocation to catch surprises.
Document lifetime expectations for collaborators.

48. What makes a good Objective-C module interface for other teams?

Minimal, stable headers with clear nullability.
Protocol-based APIs that are easy to mock.
Small set of entry points with sane defaults.
Consistent naming and predictable errors.
Versioned changes with deprecation windows.
Examples showing common usage patterns.
A contact owner for questions and incidents.

49. How do you prevent “utility class sprawl” in Objective-C?

Group helpers by domain, not a giant Utils.m.
Promote helpers to modules when they gain weight.
Delete helpers that duplicate standard APIs.
Keep public helpers documented and tested.
Avoid static methods if instance state would help.
Review new helper proposals in code reviews.
Track usage and prune dead code quarterly.

50. What’s your approach to logging without drowning in noise?

Define log levels and stick to them across modules.
Add context: request IDs, user steps, and key parameters.
Don’t log personal or sensitive data.
Collapse repetitive logs with counters or summaries.
Turn verbose logs off in production by default.
Include feature flags and app versions in logs.
Sample high-volume logs to protect performance.

51. How do you tackle crash loops caused by corrupted user data?

Detect repeated crashes on launch and enter a safe mode.
Clear or migrate only the corrupted subset, not everything.
Back up data before destructive steps.
Add integrity checks when reading stored models.
Report details so the server can fix upstream issues.
Provide a user-friendly recovery path in UI.
Add regression tests for the corrupting input.

52. When is it okay to mix Objective-C exceptions with NSError patterns?

Reserve exceptions for programmer errors, not flow control.
Use NSError** for recoverable, user-visible failures.
Don’t try/catch in hot paths; fix the root cause.
Wrap third-party calls if they throw unexpectedly.
Document which APIs may raise and why.
Convert exceptions to errors at safe boundaries.
Keep crash analytics tied to exception types.

53. How do you keep nib/storyboard outlets safe in ObjC controllers?

Annotate outlets as weak unless you own the view.
Validate outlets in viewDidLoad with assertions in debug.
Avoid heavy work inside awakeFromNib.
Keep IBOutlet wiring minimal; favor code for dynamic UI.
Use reuse identifiers consistently to avoid miswires.
Snapshot-test critical screens to catch missing outlets.
Document any non-standard wiring choices.

54. What’s your strategy to phase out outdated APIs in a legacy app?

Mark deprecated and provide the replacement immediately.
Build automated checks to block new uses of old APIs.
Create small migration tasks developers can pick up.
Track progress visibly so momentum stays high.
Celebrate teams that delete the most dead code.
Remove the old path once usage hits zero.
Keep post-mortems for lessons learned.

55. How do you evaluate a third-party SDK for an Objective-C app?

Check ObjC header quality: nullability, generics, clarity.
Validate thread safety and documented lifetimes.
Measure size impact on app and cold start.
Review license, security posture, and maintenance cadence.
Wrap it behind your protocols before adoption.
Pilot in a canary build and watch metrics.
Ensure clean uninstall if you revert.

56. What guardrails help with dynamic features toggled at runtime?

Keep default states safe and conservative.
Validate flag changes don’t break background tasks.
Cache decisions per session if servers flap.
Log flag state with errors to speed root cause.
Provide a kill switch for quick rollback.
Test toggles on low-end devices and bad networks.
Document dependencies between flags to avoid conflicts.

57. How do you make Objective-C code friendlier for new graduates?

Write small, single-purpose methods with clear names.
Prefer protocols and composition over deep inheritance.
Add comments for non-obvious runtime tricks.
Provide a starter guide on memory and ARC basics.
Pair reviews with concrete examples and Instruments demos.
Keep a glossary of common patterns in the repo.
Label good issues for newcomers to practice.

58. What’s your approach to safely removing message-sending to `nil` assumptions?

Treat nil-tolerant calls as convenience, not design.
Add guards where nil hides real failures.
Use assertions in debug to surface unexpected nil.
Prefer explicit optionals in Swift at the boundary.
Write tests that cover both present and absent cases.
Log once with context instead of silent no-ops.
Document where nil is an acceptable input.

59. How do you ensure Objective-C APIs age well as the team scales?

Keep contracts stable and versioned.
Prefer small, orthogonal APIs over mega-methods.
Enforce consistent naming across modules.
Add samples and “how-to” snippets near headers.
Deprecate with empathy and lead time.
Maintain a changelog per module, not just app-wide.
Run design reviews for public API changes.

60. What are your top lessons from years maintaining Objective-C apps?

Start from tests and measurements, not hunches.
Keep ownership rules crystal clear to avoid leaks.
Use runtime power sparingly and document it loudly.
Hide complexity behind tiny, focused interfaces.
Prefer incremental migrations with rollback paths.
Make your ObjC headers a promise you can keep.
Delete dead code often so the living code breathes.

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