UIKit views, controls, target-action, and delegation

UIKit controls are objects that hold configuration and send events. Reusable views present state and report intent. They do not decide whether a note can be saved or deleted.

Configure standard controls first

final class NoteRowView: UIView {
    private let titleLabel = UILabel()
    private let detailLabel = UILabel()

    override init(frame: CGRect) {
        super.init(frame: frame)
        titleLabel.font = .preferredFont(forTextStyle: .headline)
        titleLabel.adjustsFontForContentSizeCategory = true
        detailLabel.font = .preferredFont(forTextStyle: .subheadline)
        detailLabel.textColor = .secondaryLabel
        detailLabel.numberOfLines = 2
        configureHierarchy()
    }

    required init?(coder: NSCoder) { fatalError("init(coder:) is unavailable") }

    func apply(note: FieldNote) {
        titleLabel.text = note.title
        detailLabel.text = note.body
    }
}

apply is idempotent. Reuse can call it repeatedly without accumulating subviews, gestures, or constraints.

Send intent with target-action

private lazy var saveButton = UIButton(
    configuration: .filled(),
    primaryAction: UIAction(title: "Save") { [weak self] _ in
        self?.didRequestSave()
    }
)

private func didRequestSave() {
    guard let command = editor.makeSaveCommand() else {
        showValidationErrors()
        return
    }
    onSave?(command)
}

The action gathers input and emits a command. The use case owns validation that must remain true outside this controller and performs persistence.

Use delegation for an ongoing relationship

A text field delegate can control editing transitions and report events over time. Keep ownership explicit because delegate properties are commonly weak. Closures fit one or a few focused actions. Protocol delegates fit a reusable object with several related events.

Do not subclass a standard control only to set colors or fonts. Configuration, content configuration, and composition usually keep behavior clearer.

Reset reusable state

Rows and cells must replace text, images, accessory state, accessibility values, and pending async work when reused. A stale image task can otherwise finish into the wrong note.

Validation boundary

The UIKit snippets were not compiled. Control configuration, target-action dispatch, delegate callbacks, Dynamic Type, accessibility, and reuse remain Not verified.

Previous: Part 45: UIKit’s event-driven mental model and app lifecycle
Next: Part 47: UIKit Auto Layout, stack views, guides, and priorities
Series index: Zero to iOS Hero

References

UIControl defines control event handling.
UIButton.Configuration configures modern buttons.
Using delegates to customize object behavior explains delegation in Swift.