UIControl block call back

UIControl+Block.swift

import UIKit

extension UIControl {
    /// add handler for specific `UIControl.Event`
    func addEvent(_ event: UIControl.Event, handler: @escaping (UIControl) -> Void) {
        let holder = EventHandlerHolder(action: handler)
        retainHolder(holder, for: event)
        addTarget(holder, action: #selector(holder.invokeHandler), for: event)
    }
    
    /// remove all `handler` of specific `UIControl.Event`
    func removeHandlers(for event: UIControl.Event) {
        var dic = eventHolderDictionary
        let oldKeys = dic.keys
            .map(\.uintValue)
            .map(UIControl.Event.init(rawValue:))
        
        let eventsToModify = oldKeys.filter { $0.contains(event) } + [event]
        eventsToModify.forEach { oldEvent in
            let oldKey = NSNumber(value: oldEvent.rawValue)
            let newEvent = oldEvent.subtracting(event)
            
            if newEvent.isEmpty {
                dic[oldKey]?.forEach({ holder in
                    removeTarget(holder, action: #selector(holder.invokeHandler), for: oldEvent)
                })
                dic[oldKey] = nil
            } else {
                dic[oldKey]?.forEach({ holder in
                    removeTarget(holder, action: #selector(holder.invokeHandler), for: oldEvent)
                    addTarget(holder, action: #selector(holder.invokeHandler), for: newEvent)
                })
                let newKey = NSNumber(value: newEvent.rawValue)
                dic[newKey] = dic[oldKey]
                dic[oldKey] = nil
            }
        }
        eventHolderDictionary = dic
    }
}

private var eventHolderDictionaryKey: Void?
extension UIControl {
    private func retainHolder(_ holder: EventHandlerHolder, for event: UIControl.Event) {
        let key = NSNumber(value: event.rawValue)
        var dic = eventHolderDictionary
        let holders = dic[key] ?? []
        dic[key] = holders.union([holder])
        eventHolderDictionary = dic
    }
    
    private var eventHolderDictionary: [NSNumber: Set<EventHandlerHolder>] {
        get {
            let obj = objc_getAssociatedObject(self, &eventHolderDictionaryKey) as? [NSNumber: Set<EventHandlerHolder>]
            return obj ?? [:]
        }
        set {
            objc_setAssociatedObject(self, &eventHolderDictionaryKey, newValue, .OBJC_ASSOCIATION_COPY_NONATOMIC)
        }
    }
    
    private final class EventHandlerHolder: NSObject {
        let action: (UIControl) -> Void
        init(action: @escaping (UIControl) -> Void) {
            self.action = action
        }
        
        @objc fileprivate func invokeHandler(sender: UIControl) {
            action(sender)
        }
    }
}