Sample CodeiOS 14.0+, iPadOS 14.0+, Mac Catalyst 14.0+Reviewed 2026-07-21View on Apple Developer

Accessibility design for Mac Catalyst

At a glance

Item	Summary
Purpose	Adapt a UIKit coffee browser for keyboard, VoiceOver, semantic groups, focus groups, and Mac Catalyst conventions.
Architecture	Small UIKit MVC app with value-type view models and controller-owned screen state.
Main pattern	A cell delegate sends interaction intent to the list controller, which owns mutation and reapplies a diffable snapshot.
Boundary	One app target; there is no extension, service layer, or reusable framework target.

Project structure

RoastedBeans/
├── Model/                 # Coffee, Status, RBViewModel, sample data
├── RBListViewController.swift
├── RBCell.swift
├── RBDetailViewController.swift
├── RBStatusView.swift
└── AppDelegate.swift / SceneDelegate.swift

The folders separate data shapes from UIKit screens, but they do not create independent modules.

Overall architecture

flowchart LR
    Scene["App / scene delegates"] --> List["RBListViewController"]
    Sample["SampleData"] --> VM["RBViewModel values"]
    VM --> List
    List --> Cell["RBCell"]
    List --> Detail["RBDetailViewController"]
    Cell --> AX["Accessibility labels and custom actions"]
    Detail --> AX2["Semantic and focus groups"]

Reference code

RoastedBeans/RBListViewController.swift:56 — the list maps its controller-owned models into cells (abridged).

datasource = UITableViewDiffableDataSource(
    tableView: tableView,
    cellProvider: { [self] table, index, _ in
        let data = self.tableData[index.row]
        cell.configure(for: data)
        cell.delegate = self
        return cell
    }
)

Ownership and state

classDiagram
    RBListViewController *-- RBViewModel : tableData
    RBListViewController *-- UITableViewDiffableDataSource
    RBListViewController --> RBCell : configures
    RBCell o-- RBCellActionProtocol : weak delegate
    RBDetailViewController *-- RBViewModel : screen copy

Ownership evidence

RoastedBeans/RBCell.swift:9 and RoastedBeans/RBCell.swift:22 — the child reports actions without owning the controller.

protocol RBCellActionProtocol: AnyObject {
    func didIncreaseRating(cell: RBCell)
    func didToggleFavorite(cell: RBCell)
}

weak var delegate: RBCellActionProtocol?

The list controller is the mutation authority for tableData; the detail controller receives and mutates its own value copy. There is no shared persistence layer.

Class and protocol design

RBListViewController and RBDetailViewController are final UIKit subclasses. RBViewModel is a Hashable struct suitable for diffable identity. The app-defined RBCellActionProtocol: AnyObject is a narrow protocol-oriented boundary for cell events; RBListViewController adopts it in an extension at RoastedBeans/RBListViewController.swift:96.

Access control

Symbol	Access	Why it fits
`tableData`, `datasource`	`private`	Only the list controller may mutate and publish its snapshot (`RoastedBeans/RBListViewController.swift:11`).
Cell outlets and formatting helpers	`private`	Storyboard wiring and presentation details stay inside `RBCell` (`RoastedBeans/RBCell.swift:24`).
`delegate`	internal, weak	The sibling controller must assign it; weak ownership avoids a cell/controller cycle.
App types	internal by default	A single app target has no public API surface.

No public or fileprivate API is needed. private is used for implementation details; default internal access joins files within the target.

Logic ownership and placement

Logic	Owner	Placement reason
Rating/favorite mutation and snapshot refresh	`RBListViewController`	It owns collection state and table coordination.
Cell accessibility value/actions	`RBCell`	They derive directly from cell presentation (`RoastedBeans/RBCell.swift:147`).
Detail semantic groups and focus identifiers	`RBDetailViewController`	They describe that screen’s custom hierarchy (`RoastedBeans/RBDetailViewController.swift:60`).
Sample construction	`SampleData`	Static fixture generation stays next to model types (`RoastedBeans/Model/RBViewModel.swift:105`).

Design patterns

Pattern	Evidence	Tradeoff
Delegate	Cell action protocol and weak reference	Keeps reusable cell interaction-free, with some controller coupling through `RBCell`.
Diffable data source	Snapshot reapplied after mutation	Stable identity and simple UI refresh; the controller remains state-heavy.
View model value	`RBViewModel` combines domain and display state	Convenient for a sample, but detail changes do not flow back automatically.
Controller coordinator	List creates and shows detail	Appropriate for two screens; no separate router abstraction.

Naming conventions

The RB prefix scopes app-specific UIKit types (RBCell, RBStatusView, RBViewModel).
Event methods start with did...; configuration methods start with configure... or setup....
Model nouns are singular; collections use plural names such as coffees, statuses, and locationsAvailable.

Architecture takeaways

Put mutation in the controller that owns the diffable snapshot.
Use a weak, class-bound delegate for reusable child-view actions.
Keep accessibility semantics next to the custom presentation they describe.
This is a compact single-target teaching app, not a reusable Catalyst architecture package.

Source map

Source	Role
`RoastedBeans/Model/RBViewModel.swift:10`	Value view model and identity
`RoastedBeans/RBListViewController.swift:136`	Favorite mutation and snapshot
`RoastedBeans/RBCell.swift:187`	Accessibility custom actions
`RoastedBeans/RBDetailViewController.swift:141`	Custom navigation semantic group
`RoastedBeans/AppDelegate.swift:9`	App entry point

Official Apple documentation