SelectableButton.swift

class ViewController: UIViewController {
  override func viewDidLoad() {
    super.viewDidLoad()
    let button = CustomButton()
    self.view.addSubview(button)
    button.translatesAutoresizingMaskIntoConstraints = false
    button.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 50).isActive = true
    button.leftAnchor.constraint(equalTo: self.view.leftAnchor, constant: 20).isActive = true
    button.setTitle("Click Here", for: .normal)
    button.setTitleColor(.black, for: .normal)
    button.addTarget(self, action: #selector(toggleAction(sender:)), for: .touchUpInside)
  }
  @objc func toggleAction(sender: CustomButton){
    sender.selectedFlag.toggle()
      if sender.selectedFlag{
        sender.backgroundColor = .green
      } else {
        sender.backgroundColor = .clear
      }
   }
}


class CustomButton: UIButton{
  var selectedFlag = false
}