title: Button touch Event
body: <p>Please check the below code. 
  I made button on mainView. 
  But the button doesn't call "thumbsUpButtonPressed" method. 
  Please check it!</p>
  
  <pre><code>override func viewDidLoad() {
      super.viewDidLoad()
  
      let button = UIButton(type: .custom)
      button.frame = CGRect(x: 60, y: 100, width: 50, height: 50)
  
      button.backgroundColor = .red //.clear
      button.layer.cornerRadius = 5
      button.layer.borderWidth = 1
      button.layer.borderColor = UIColor.black.cgColor
  
      button.clipsToBounds = true
      //button.setImage(UIImage(named:"thumbsUp.png"), for: .normal)
      button.addTarget(self, action: #selector(thumbsUpButtonPressed), for: .touchDown)
  
      view.addSubview(button)
  }
  
  func thumbsUpButtonPressed(sender: UIButton) {
      print("thumbs up button pressed")
  }
  </code></pre>