Set primary action handler on UIButton and UIBarButtonItem

PrimaryActionHandler.swift

import UIKit

public extension UIAction.Identifier {
	static let primary = UIAction.Identifier(rawValue: "PrimaryAction")
}

fileprivate extension UIAction {
	var handler: UIActionHandler? {
		// Tiny bit sketchy: cast UIAction's "handler" value to a ObjC block
		typealias ActionHandlerBlock = @convention(block) (UIAction) -> Void
		let handler = value(forKey: "handler") as AnyObject
		return unsafeBitCast(handler, to: ActionHandlerBlock.self)
	}
	static func primary(_ handler: @escaping UIActionHandler) -> UIAction {
		UIAction(identifier: .primary, handler: handler)
	}
}

public protocol PrimaryActionSetting {
	@MainActor var primaryAction: UIAction? { get }

	/// The handler associated with a `UIAction` with the `.primary` identifier
	@MainActor var actionHandler: UIActionHandler? { get set }

	/// Updates 'primary' action set to the receiver
	/// - Parameter handler: Handler executed with the primary action
	@MainActor func setActionHandler(_ handler: UIActionHandler?)
}

extension UIControl: PrimaryActionSetting {
	public var primaryAction: UIAction? {
		var primaryAction: UIAction?
		// Find action that is set as primary
		enumerateEventHandlers { action, _, _, stop in
			guard action?.identifier == .primary else {
				return
			}
			primaryAction = action
			stop = true
		}
		return primaryAction
	}

	public var actionHandler: UIActionHandler? {
		get {
			primaryAction?.handler
		}
		set {
			setActionHandler(newValue)
		}
	}

	public func setActionHandler(_ handler: UIActionHandler?) {
		removeAction(identifiedBy: .primary, for: .touchUpInside)
		handler.map { addAction(.primary($0), for: .touchUpInside) }
	}
}

extension UIBarButtonItem: PrimaryActionSetting {
	public var actionHandler: UIActionHandler? {
		get { primaryAction?.handler }
		set { setActionHandler(newValue) }
	}

	public func setActionHandler(_ handler: ((UIAction) -> Void)?) {
		primaryAction = handler.map { .primary($0) }
	}
}