Sample CodeiOS 12.0+, iPadOS 12.0+, Mac Catalyst 12.0+Reviewed 2026-07-23View on Apple Developer

Delivering an exceptional accessibility experience

At a glance

Item	Summary
Purpose	Demonstrate custom actions, adjustable elements, grouped statistics, modal accessibility, and change notifications.
Architecture	One UIKit view controller coordinates a small model and several specialized views.
State strategy	`currentlyFocusedDog` is the controller’s source of truth and propagates to the carousel, statistics, and shelter views.
Boundary	Single app target; no extension, persistence service, or custom protocol layer.

Project structure

ExceptionalAccessibility/
├── ViewController.swift
├── Dog.swift
├── DogCarouselContainerView.swift
├── DogStatsView.swift
├── DogModalView.swift
└── DogCollectionViewCell.swift

Files are organized by screen component rather than formal architectural layers.

Overall architecture

flowchart LR
    VC["ViewController"] --> Dogs["Dog values"]
    VC --> Collection["UICollectionView"]
    VC --> Carousel["DogCarouselContainerView"]
    VC --> Stats["DogStatsView"]
    VC --> Modal["DogModalView"]
    Carousel --> AX["CarouselAccessibilityElement"]
    Stats --> Grouped["Grouped UIAccessibilityElement values"]

Reference code

ExceptionalAccessibility/ViewController.swift:32 — one property broadcasts the selected model (abridged).

var currentlyFocusedDog: Dog? {
    didSet {
        dogStatsView.dog = currentlyFocusedDog
        carouselContainerView.currentDog = currentlyFocusedDog
        shelterNameLabel.text = currentlyFocusedDog?.shelterName
        shelterInfoView.accessibilityLabel = currentlyFocusedDog?.shelterName
    }
}

Ownership and state

classDiagram
    ViewController *-- Dog : dogs
    ViewController o-- DogCarouselContainerView : outlet
    ViewController o-- DogStatsView : outlet
    DogCarouselContainerView *-- CarouselAccessibilityElement : cached
    DogStatsView *-- UIAccessibilityElement : cached group
    CarouselAccessibilityElement o-- DogCarouselContainerView : accessibilityContainer

Ownership evidence

ExceptionalAccessibility/DogCarouselContainerView.swift:189 — the container lazily owns and invalidates its accessibility projection (abridged).

private var _accessibilityElements: [Any]?

override var accessibilityElements: [Any]? {
    if _accessibilityElements == nil {
        let element = CarouselAccessibilityElement(
            accessibilityContainer: self,
            dog: currentDog
        )
        self.carouselAccessibilityElement = element
    }
    return _accessibilityElements
}

The controller owns selection state. Each custom view owns only the accessibility objects derived from its current dog and clears its cache when that input changes.

Class and protocol design

The sample uses concrete UIKit subclasses: CarouselAccessibilityElement: UIAccessibilityElement, DogCarouselContainerView: UIView, and DogStatsView: UIView. ViewController directly adopts framework data-source/delegate protocols at ExceptionalAccessibility/ViewController.swift:15. There is no app-defined protocol because the components communicate through outlets and properties.

Access control

Symbol	Access	Why it fits
`_accessibilityElements` in carousel/stats	`private`	Cache consistency must remain inside each view (`ExceptionalAccessibility/DogStatsView.swift:52`).
Most outlets and model state	internal default	Storyboard wiring and the small sample share them across files.
`Dog` fields	internal	The value is target-local and directly rendered by several views.
Public API	none	The archive builds an application, not a library.

The underscore marks a backing cache; private enforces its invalidation contract. Broader internal visibility is educational convenience, not a published surface.

Logic ownership and placement

Logic	Owner	Placement reason
Current-dog propagation and collection scrolling	`ViewController`	It coordinates all screen components.
Adjustable VoiceOver behavior	`CarouselAccessibilityElement`	It is the semantic replacement for the carousel (`ExceptionalAccessibility/DogCarouselContainerView.swift:133`).
Grouping label pairs	`DogStatsView`	It knows label frames and content.
Modal isolation	`DogModalView`	The overlay declares itself modal at `ExceptionalAccessibility/DogModalView.swift:51`.

Design patterns

Pattern	Evidence	Purpose
Coordinator-by-controller	`currentlyFocusedDog.didSet`	Synchronizes multiple views from one selection.
Accessibility adapter	Custom element turns a collection into an adjustable picker	Changes semantics without changing the visual UI.
Cached derived view	Accessibility element arrays persist until input changes	Gives VoiceOver stable object identity.
Framework delegate	Collection protocols on the controller	Keeps the small screen direct.

Naming conventions

Domain names (Dog) stay separate from UI role suffixes (View, ViewController, Element).
currentDog and currentlyFocusedDog communicate selection semantics.
Accessibility overrides retain UIKit’s framework vocabulary.

Architecture takeaways

Keep one authoritative selection and push it to dependent components.
Cache custom accessibility elements when assistive navigation requires stable identity.
Place geometry-aware accessibility grouping inside the owning view.
The design is intentionally concrete and code-light; extra service or protocol layers would obscure the examples.

Source map

Source	Role
`ExceptionalAccessibility/Dog.swift:13`	Domain value and fixtures
`ExceptionalAccessibility/ViewController.swift:45`	Custom actions and screen coordination
`ExceptionalAccessibility/DogCarouselContainerView.swift:22`	Adjustable custom element
`ExceptionalAccessibility/DogStatsView.swift:28`	Input-driven cache invalidation
`ExceptionalAccessibility/DogModalView.swift:38`	Overlay lifecycle
`ExceptionalAccessibility/AppDelegate.swift:9`	App entry point

Official Apple documentation