📱 Mobile Dev

Run a Core ML image model with Vision

Add the .mlmodel so Xcode generates a class, wrap it in a VNCoreMLModel, run a VNCoreMLRequest via a VNImageRequestHandler, read results off the main queue.

Track location continuously in the background

Set desiredAccuracy, distanceFilter, activityType; enable the Location background mode and allowsBackgroundLocationUpdates; request Always authorization.

Play a remote video with AVFoundation

Wrap the URL in AVPlayerItem, feed it to AVPlayer, render with AVPlayerLayer added to the view's layer (or AVPlayerViewController for controls).

Request the user's location one time

Add a usage description to Info.plist, set a CLLocationManager delegate, request when-in-use authorization, call requestLocation, handle didUpdateLocations and didFailWithError.

Animate a SwiftUI Shape morphing point count

Expose a continuous sides value as animatableData so SwiftUI interpolates it, then compute the path from that fractional value each frame.

Build an interruptible custom VC transition

A delegate vends an animator (UIViewControllerAnimatedTransitioning) for the visuals and an interactive controller (UIViewControllerInteractiveTransitioning) driven by a pan to scrub progress and…

Diagnose dropped frames during animation

Use Core Animation and color-debug options to spot off-screen passes, blending, and overdraw; cache, flatten, and set shadowPath.

Allow simultaneous pan and pinch gestures

Attach pan and pinch recognizers, set yourself as delegate, return true from shouldRecognizeSimultaneouslyWith, apply translation to center and scale to transform.

Build a custom circular progress bar in UIKit

Draw an arc with UIBezierPath, assign it to a CAShapeLayer path, set lineWidth and no fill, animate strokeEnd 0 to 1.

Difference between frame, bounds, and center

Frame and center are in the superview's space; bounds is the view's own space, usually origin zero. A non-identity transform makes frame undefined to read.

Add shadow and rounded corners to a UIView

CornerRadius needs masksToBounds true, but that clips the shadow; set shadowPath to keep both and stay performant.

Implicit .animation() vs explicit withAnimation

.animation(value:) animates a view when a tracked value changes; withAnimation wraps the state mutation so all dependent views animate.

What is an actor and how does it prevent data races

Actors serialize access to mutable state, reachable only via await; compiler blocks unsafe access. Token-refresh actor coalesces concurrent refreshes.

How task cancellation works with async/await

Cancellation is a flag, not a kill; check Task.isCancelled or call checkCancellation, URLSession throws CancellationError automatically.

Add a default header to every URLSession request

Set httpAdditionalHeaders on a URLSessionConfiguration, build the session from it, mention per-request overrides win.

What is @MainActor and why does it matter?

@MainActor is a global actor guaranteeing code runs on the main thread; annotate UI-updating types or methods so post-network state changes are main-thread safe.

intermediate2 min read

Run two API calls concurrently with async let

Use async let to start two independent fetches that run concurrently, then await both, so total time approaches the slower call rather than the sum.

intermediate2 min read

URLSession data vs download vs upload tasks

Data tasks buffer responses in memory for small API calls; download tasks stream to a file and support background transfers for large files; upload tasks send bodies from data or files and report…

Map JSON keys to differently named Codable properties

Declare a nested CodingKeys enum mapping userID to the raw value "user_id", or set the decoder's keyDecodingStrategy to convertFromSnakeCase for blanket conversion.