title: How to change its own button image on tap in Swift
body: <p>Now i have an button with an image,
  I wanted to change the button image when I tap the button.
  How to change its own button image on tap in Swift</p>
  
  <p>do i need to add an outlet?</p>
  
  <pre><code>@IBOutlet weak var btnSmiley: UIButton!
  
  @IBAction func btnSmiley(sender: AnyObject) {
      btnSmiley.image = UIImage(named: "smiley")
  }
  </code></pre>