📱Mobile Dev

Mobile app development across platforms

1327 bites

Test yourself: Top 30 Mobile Dev interview questions →Multiple choice, with the correct answer and why it is correct on every question. Free, no sign-in.

Everything in Mobile Dev, page 9

intermediate1 min read

Decoding a heterogeneous JSON array by a type field

Peek the type field with a partial decode, switch on it, and decode the concrete type, wrapping each in an enum or boxed protocol value.

intermediate1 min read

Minimizing Storyboard merge conflicts

Split into many small storyboards or xibs, or move to programmatic or SwiftUI layout; process-wise coordinate ownership and merge often.

intermediate2 min read

Faulting in Core Data

A fault is a placeholder object whose property data is not yet loaded; accessing a property fires the fault and fetches from the store, saving memory.

intermediate2 min read

View identity in SwiftUI and the .id() modifier

Identity links a view to its persistent state and transitions; structural identity comes from position, explicit identity from .id(); changing the id resets state and forces a new view.

intermediate1 min read

Copy-on-write and implementing it for a custom struct

CoW shares a buffer until mutation, deep-copying only when the buffer is non-unique; Array, Dictionary, Set, String use it; implement with a class storage box and isKnownUniquelyReferenced.

intermediate1 min read

map versus compactMap versus flatMap

Map transforms each element one-to-one; compactMap transforms then drops nils; flatMap transforms to sequences then concatenates.

advanced2 min read

Debugging a closure capture leak in a third-party library

Use the Memory Graph Debugger to inspect retain paths, the Leaks and Allocations instruments, and malloc stack logging; trace the cycle before patching.

advanced2 min read

Verifying and avoiding copy-on-write overhead

Confirm extra copies via isKnownUniquelyReferenced or instruments and the retain trace; ensure unique references, mutate inout/in place, reserveCapacity, avoid aliasing.

advanced1 min read

The dynamic keyword and message dispatch

Dynamic forces Objective-C message dispatch via objc_msgSend, enabling KVO and swizzling, at the cost of skipping inlining and devirtualization.

intermediate1 min read

dispatch_async versus Task.detached for offloading work

Dispatch_async submits a closure to a queue; Task.detached starts an unstructured async task off the current actor without inheriting context.

intermediate1 min read

What an autoreleasepool is and when to add one manually

An autorelease pool holds objects until it drains; wrap tight loops creating many temporary ObjC objects in autoreleasepool to cap peak memory.

intermediate1 min read

Exposing Swift classes to Objective-C

Subclass NSObject or mark members @objc, import the generated ModuleName-Swift.h, and accept that Swift-only types like enums with associated values cannot cross.

intermediate1 min read

Struct versus class performance and memory tradeoffs

Structs are value types, often stack-allocated with no ARC; classes are heap-allocated reference types with retain counts.

easy1 min read

Diagnosing choppy scrolling performance

Reach for Instruments, especially the Time Profiler and Core Animation/Hangs tools, and look for main-thread work and dropped frames.

easy1 min read

Purpose and setup of an Objective-C bridging header

The bridging header imports ObjC headers into Swift; Xcode auto-creates it or you add it manually and set the build setting.

advanced2 min read

Privacy manifests and the app privacy report

PrivacyInfo.xcprivacy declares collected data types, tracking, and reasons for required-reason APIs; Xcode aggregates your manifest plus SDK manifests into a privacy report.

advanced2 min read

Securely managing signing assets in CI/CD

Keep encrypted certificates and profiles in a controlled store or fastlane match repo, inject the decryption key and credentials via CI secrets, install into a temporary keychain per run.

advanced1 min read

App Thinning: slicing, bitcode, and on-demand resources

Slicing delivers only the assets and code a device needs; bitcode let Apple recompile and re-optimize; on-demand resources defer large assets until requested.

intermediate1 min read

Automatic signing: benefits and limitations on teams

Automatic signing creates certificates and profiles on demand and keeps them in sync, easing local setup; limits include proliferating certificates, weak CI fit, and less control for complex entitlements.

intermediate1 min read

Phased release to limit update risk

Enable phased release so an approved update reaches a growing percentage of automatic-update users over seven days; pause if metrics spike.

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