Ios Uikit Expert

Rules

• Respect lifecycle boundaries and keep side effects predictable.
• Prefer clear constraints over fragile frame mutation.
• Do not bury business logic inside view controllers.
• Reset reused views completely.
• Be explicit about containment and ownership when embedding child controllers.
• Prefer UIContentConfiguration over legacy cell properties for iOS 14+ targets.
• Use UICollectionViewCompositionalLayout for new collection view work on iOS 13+.
• Keep UIHostingController bridging narrow — avoid deep SwiftUI trees inside UIKit containers without explicit sizing.

Recommended patterns

• Dedicated configuration methods for cells and reusable views
• Coordinator or routing ownership outside leaf controllers
• Testable presenter or view model logic away from the controller
• Constraint sets that document intended layout states

Common failure modes

• Work is done before the view hierarchy is ready
• Reused cells leak prior state
• Constraints fight because ownership is split across multiple methods
• Appearance callbacks are used as unreliable state synchronization
• Hosted SwiftUI and UIKit each assume the other owns lifecycle

API availability notes

• iOS 13+: UICollectionViewCompositionalLayout, DiffableDataSource, UIHostingController, scene lifecycle
• iOS 14+: UIContentConfiguration, UIAction-based menus, UIColorPickerViewController, UIListContentConfiguration
• iOS 15+: UISheetPresentationController, UIButton.Configuration, UITableView.sectionHeaderTopPadding
• iOS 16+: UIHostingConfiguration (SwiftUI cells in UIKit collections), UICalendarView, self-resizing cells by default
• iOS 17+: Animated symbol images, UIContentUnavailableConfiguration, trait registration

Examples

Cell configuration — Do

// iOS 14+: use UIContentConfiguration
func configure(with item: Item) {
    var config = UIListContentConfiguration.cell()
    config.text = item.title
    config.secondaryText = item.subtitle
    config.image = UIImage(systemName: item.icon)
    contentConfiguration = config
}

Cell configuration — Don't

// Legacy: direct property access breaks with modern cell lifecycle
func configure(with item: Item) {
    textLabel?.text = item.title
    detailTextLabel?.text = item.subtitle
    imageView?.image = UIImage(systemName: item.icon)
}

Child view controller containment — Do

func embed(_ child: UIViewController) {
    addChild(child)
    view.addSubview(child.view)
    child.view.translatesAutoresizingMaskIntoConstraints = false
    NSLayoutConstraint.activate([
        child.view.topAnchor.constraint(equalTo: view.topAnchor),
        child.view.bottomAnchor.constraint(equalTo: view.bottomAnchor),
        child.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
        child.view.trailingAnchor.constraint(equalTo: view.trailingAnchor)
    ])
    child.didMove(toParent: self)
}

Child view controller containment — Don't

// Wrong: missing lifecycle calls and constraint setup
func embed(_ child: UIViewController) {
    view.addSubview(child.view)
    child.view.frame = view.bounds
    // Missing: addChild, didMove(toParent:), autoresizing
}

Output standard

• Identify the relevant lifecycle or layout boundary
• Explain the regression in UIKit terms
• Prefer a local fix over controller-wide rewrites