Swift UIKit Skill

Operating Rules

• All UI is built programmatically (no Storyboards). Always set translatesAutoresizingMaskIntoConstraints = false.
• Prefer NSLayoutConstraint.activate([...]) for batch constraint activation.
• Organize view controller code with extensions: separate style(), layout(), and protocol conformances.
• Use factory functions for repetitive UI element creation.
• Use weak references for delegates and [weak self] in closures to prevent retain cycles.
• Prefer Result<Success, Error> for async completion handlers.
• Always dispatch UI updates to the main thread from async callbacks.
• Extract custom views flush to their container; parent manages spacing.
• Use child view controllers for complex, self-contained screen sections.
• Consult relevant reference files before implementing any topic.

Task Workflow

Review existing UIKit code

• Read the code under review and identify which topics apply
• Run the Topic Router below for each relevant topic
• Check for retain cycles (missing weak delegates, missing [weak self])
• Verify Auto Layout completeness (unambiguous constraints, no warnings)
• Flag deprecated patterns (e.g., manual beginUpdates/endUpdates when Diffable is available)

Improve existing UIKit code

• Audit current implementation against the Topic Router topics
• Extract large view controllers into child VCs and custom views
• Replace inline UI creation with factory functions
• Migrate legacy table/collection view data sources to Diffable where appropriate
• Add proper error handling with Result types

Implement new UIKit feature

• Design data flow first: identify service, view model, view controller, and view layers
• Structure views for composition (extracted views + child view controllers)
• Apply correct animation patterns (constraint-based, Core Animation, or UIView)
• Use protocol-delegate for sustained relationships; closures for one-shot callbacks
• Add proper loading/error states

Topic Router

Consult the reference file for each topic relevant to the current task:

Topic	Reference
UITableView	references/uitableview.md
UICollectionView	references/uicollectionview.md
UINavigationController	references/uinavigationcontroller.md
UIScrollView	references/uiscrollview.md
Core Animation	references/core-animation.md
Core Graphics	references/core-graphics.md
Auto Layout animation	references/auto-layout-animation.md
Communication patterns	references/communication-patterns.md
Architecture patterns	references/architecture-patterns.md
View extraction	references/view-extraction.md
Navigation patterns	references/navigation-patterns.md
Design patterns (UI)	references/design-patterns.md
Networking	references/networking.md
Factory functions	references/factory-patterns.md
Nib / XIB patterns	references/nib-patterns.md
NSAttributedString	references/nsattributedstring.md
Gesture recognizers	references/gesture-recognizers.md
Custom controls	references/custom-controls.md
Currency formatting	references/currency-formatting.md
Deep linking	references/deep-linking.md

Correctness Checklist

These are hard rules -- violations are always bugs:

• Every programmatic view sets translatesAutoresizingMaskIntoConstraints = false
• Delegates are declared weak var delegate: SomeDelegate?
• Async closures capture [weak self] when referencing the owning object
• UI updates from async callbacks are dispatched to DispatchQueue.main
• beginUpdates() / endUpdates() bracket all batch table view mutations
• Diffable data source items conform to Hashable with stable identifiers
• Child view controllers follow the 3-step lifecycle: addChild(), addSubview(), didMove(toParent:)
• Custom views define intrinsicContentSize when they have a natural size
• NSFetchedResultsController delegate implements all three callbacks (willChange, didChange, didChangeContent)
• Core Animation model layer is updated after animation to persist final state
• NSLayoutConstraint.activate() is used instead of isActive = true one-by-one
• Factory functions return views with translatesAutoresizingMaskIntoConstraints already set to false

Quick Diagnostics

Symptom	Likely cause	Reference
View doesn't appear	Missing translatesAutoresizingMaskIntoConstraints = false	references/view-extraction.md
Table view crashes on insert	Data source count mismatch with beginUpdates	references/uitableview.md
Animation snaps to final state	Model layer not updated after CA animation	references/core-animation.md
Retain cycle / memory leak	Missing weak on delegate or [weak self]	references/communication-patterns.md
Scroll view doesn't scroll	Missing content size or broken constraint chain	references/uiscrollview.md
Shadow clipped by view	masksToBounds = true on layer	references/core-animation.md
Gradient/shadow wrong size	Set bounds-dependent layers in viewDidAppear	references/core-animation.md
Collection view empty	Forgot to register cell or data source nil	references/uicollectionview.md
Core Data threading crash	Accessing managed object on wrong queue	references/networking.md
Navigation bar title missing	Not setting title or navigationItem.title	references/uinavigationcontroller.md