Mobile Engineering Agents

Appearance

iOSUIKit

Standard: UIKit Standards ​

Rules for programmatic UIKit + MVP screens on legacy targets (iOS 13+). Complements coding_standards.md and architecture_standards.md.

Screen Structure ​

The four-file convention is mandatory for every screen:

  • <Name>Contract.swift — holds the view and presenter protocols, and nothing else.
  • <Name>View.swift — a UIView subclass owning all layout and subviews.
  • <Name>ViewController.swift — owns lifecycle and forwards to the presenter.
  • <Name>Presenter.swift — has no UIKit import.
swift
// ProfileContract.swift
protocol ProfileViewProtocol: AnyObject {
    func display(name: String)
    func showError(_ message: String)
}

protocol ProfilePresenterProtocol: AnyObject {
    func viewDidLoad()
    func didTapSave()
}

Layout ​

  • Programmatic only; Interface Builder is permitted for the launch screen and nothing else.
  • Build constraints once in the view's initializer, never in layoutSubviews.
  • Set translatesAutoresizingMaskIntoConstraints = false on every added subview.
  • Prefer layout guides over magic numbers.
swift
private func setUpConstraints() {
    titleLabel.translatesAutoresizingMaskIntoConstraints = false
    addSubview(titleLabel)

    NSLayoutConstraint.activate([
        titleLabel.topAnchor.constraint(equalTo: safeAreaLayoutGuide.topAnchor, constant: 16),
        titleLabel.leadingAnchor.constraint(equalTo: layoutMarginsGuide.leadingAnchor),
        titleLabel.trailingAnchor.constraint(equalTo: layoutMarginsGuide.trailingAnchor)
    ])
}

Adaptive Layout (iPhone Duo) ​

Screens must resize across the iPhone Duo outer display (compact width) and inner display (regular width), and when folded or in Split View. Full guidance: skills/ui/ios/iphone_duo_adaptive_layout.md.

  • Never use UIDevice.userInterfaceIdiom, UIInterfaceOrientation, or UIScreen bounds for layout decisions. Track horizontalSizeClass/verticalSizeClass with automatic trait tracking and lay out against the view's bounds.
  • Pin content to safeAreaLayoutGuide/layoutMarginsGuide. A vertical bar adds an asymmetric leading or trailing inset.
  • Put bar items on navigationItem (hosted by a UINavigationController). Never build a custom UIToolbar/UINavigationBar/UITabBar, because those can't move to the vertical bar.
  • Create items with both a title and an image (UIBarButtonItem(title:image:primaryAction:)). Pin Done in pinnedTrailingGroup, group items in UIBarButtonItemGroup, set visibilityPriority, and put rare actions in additionalOverflowItems.
  • Prefer UISplitViewController and UIArrangementViewController for two-pane content. Custom views avoid active regions from reservedRegions(kind:) by updating constraint constants, never by creating constraints in layoutSubviews.
  • Override preferredVerticalBarBehavior to return .disabled only for full-screen, non-scrolling UI.

View Controller Lifecycle ​

  • One-time setup happens in viewDidLoad; anything that must repeat on re-entry goes in viewWillAppear.
  • Never start network work from init.
  • Never put business rules in a lifecycle method — forward to the presenter.

Cells and Reuse ​

  • Register cell classes by type, never by string literal.
  • Implement prepareForReuse for any cell holding mutable state or an in-flight image load.
  • Prefer UITableViewDiffableDataSource / UICollectionViewDiffableDataSource (available from iOS 13) over manual reloadData().

Presenters ​

  • Mark @MainActor.
  • Hold the view weak.
  • Expose state as private(set).
  • Accept every dependency through the initializer as a protocol.
swift
@MainActor
final class ProfilePresenter: ProfilePresenterProtocol {
    private weak var view: ProfileViewProtocol?
    private let repository: ProfileRepositoryProtocol
    private(set) var state: ProfileState = .idle

    init(view: ProfileViewProtocol, repository: ProfileRepositoryProtocol) {
        self.view = view
        self.repository = repository
    }

    func viewDidLoad() {
        Task { await load() }
    }

    func didTapSave() {}

    private func load() async {
        // fetch via repository, then update state and call the view
    }
}

Accessibility ​

  • Set accessibilityLabel on every interactive control.
  • Set accessibilityIdentifier on anything a UI test drives.
  • Support Dynamic Type with UIFont.preferredFont(forTextStyle:) and adjustsFontForContentSizeCategory = true.