title: Finding the direction of touchDragInside sent event on UIButton
body: <p>A <code>UIButton</code> has a sent event acton <code>touchDragInside</code> (Touch Drag Inside). The button can be connected to a number of actions, for example:</p>
  
  <pre><code>@IBAction func dragButton(sender: UIButton) {
      ...
  }
  </code></pre>
  
  <p>An answer should focus on determining drag direction, left, right, up, down, in Swift coding.</p>
  
  <p>There's not a whole lot of information in the developer notes: <a href="https://developer.apple.com/documentation/uikit/uicontrolevents/1618240-touchdraginside" rel="nofollow noreferrer">https://developer.apple.com/documentation/uikit/uicontrolevents/1618240-touchdraginside</a></p>
  
  <hr>
  
  <p><strong>Question:</strong></p>
  
  <p><strong>How can I determine the actual drag direction when I tap and drag on a <code>UIButton</code> for the sent event action <code>touchDragInside</code>?</strong></p>