関連づけられたラベルの色をステートに合わせて変えるUIButton。ハイライト時のフェードアニメーション付き

MyButton.swift

import UIKit

class MyButton: UIButton {

    @IBOutlet weak var associatedLabel: UILabel? {
        didSet {
            associatedLabel?.textColor = currentTitleColor
        }
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)
    }

    override var isHighlighted: Bool {
        didSet {
            UIView.animate(withDuration: 0.2) {
                let alpha: CGFloat = self.isHighlighted ? 0.3 : 1
                self.alpha = alpha
                self.associatedLabel?.alpha = alpha
            }

            associatedLabel?.textColor = currentTitleColor
        }
    }

    override var isEnabled: Bool {
        didSet {
            associatedLabel?.textColor = currentTitleColor
        }
    }

    override var isSelected: Bool {
        didSet {
            associatedLabel?.textColor = currentTitleColor
        }
    }

    override func point(inside point: CGPoint, with event: UIEvent?) -> Bool {

        guard let label = associatedLabel else {
            return super.point(inside: point, with: event)
        }

        let labelBounds = convert(label.bounds, from: label)
        let unionBounds = bounds.union(labelBounds)

        return unionBounds.contains(point)
    }
}