Add closure targets to UIControl subclasses.

EZAction.swift

import UIKit

public typealias Action = (UIControl) -> Void

extension NSObject {
    var uniqueId: String {
        return String(describing: self)
    }
}

private struct AssociatedKey {
    static var key = "EZAction_TargetContainer"
}

// MARK: - EZAction
public protocol EZAction: class {
    associatedtype EZActionHost: AnyObject
    var targetContainer: TargetContainer<EZActionHost> { get }
}


extension EZAction {
    public var targetContainer: TargetContainer<Self> {
        get {
            if let value = objc_getAssociatedObject(self, &AssociatedKey.key) as? TargetContainer<Self> {
                return value
            }
            let value = TargetContainer(host: self)
            objc_setAssociatedObject(self, &AssociatedKey.key, value, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
            return value
        }
    }
}

// MARK: TargetContainer
public class TargetContainer<Host: AnyObject>: NSObject {
    public unowned let host: Host
    
    public init(host: Host) {
        self.host = host
    }
    
    // Keep all targets alive
    public var targets = [String: NSObject]()
}


public extension TargetContainer where Host: UIControl {
    func addAction(_ action: @escaping Action, for event: Host.Event) {
        let target = UIControlTarget(host: host, action: action, event: event)
        targets[target.uniqueId] = target
    }
}

class UIControlTarget: NSObject {
    var action: Action?

    init(host: UIControl, action: @escaping Action, event: UIControl.Event) {
        super.init()
        self.action = action
        host.addTarget(self, action: #selector(handleEvent), for: event)
    }
    
    // MARK: - Action
    @objc func handleEvent(_ sender: UIControl) {
        action?(sender)
    }
}

// MARK: Extensions
extension NSObject: EZAction { }

extension EZAction where Self: UIControl {
    public func on(_ event: Self.Event, action: @escaping Action) {
        self.targetContainer.addAction(action, for: event)
    }
    
    public func on(_ event: Self.Event, action: @escaping () -> Void) {
        self.targetContainer.addAction({ _ in action() }, for: event)
    }
}