title: Adding views dynamically to UIStackview
body: <p>I'm trying to add views(or buttons) to <code>UIStackView</code> dynamically.</p>
  
  <p>At first, the <code>UIStackView</code> has no arranged views (vertically), and 
  after getting from some http response, several views(buttons) are added to <code>UIStackView</code>. 
  <code>UIStackView</code> is also autolayout to hold a specific area. 
  I've tried to find dynamic adding example, but failed.</p>
  
  <p>Anyone can show me the examples of adding view onto <code>UIStackView</code> dynamically?</p>