Adds to UIButton selecting / deselecting on touch up feature. Useful for checkmark / agreements buttons.

UIButton+SelectionToggling.swift

extension UIButton {
    
    var isTogglingSelection: Bool {
        get {
            return target(forAction: #selector(_touchedInside), withSender: self) != nil
        }
        set {
            if isTogglingSelection {
                addTarget(self, action: #selector(_touchedInside), for: .touchUpInside)
            } else {
                removeTarget(self, action: #selector(_touchedInside), for: .touchUpInside)
            }
        }
    }
    
    @objc private func _touchedInside(_ sender: UIButton) {
        isSelected = !isSelected
    }
}