title: IGListKit: get the currently visible cell index
body: <p>I am trying to use <code>IGListKit</code> (<a href="https://github.com/Instagram/IGListKit" rel="nofollow noreferrer" title="Link">Link</a>) in iOS to render custom collection view and table view, where I have a horizontal scrollview in a section controller. In this horizontal scrollview, I need to get the index of the currently visible cells. </p>
  
  <p>I tried to use the <code>displayDelegate</code> in the section controller, but it seems to me that the following delegate method is triggered only once when the section controller is initially loaded:</p>
  
  <pre><code>func listAdapter(_ listAdapter: IGListAdapter, willDisplay sectionController: IGListSectionController, cell: UICollectionViewCell, at index: Int)
  </code></pre>
  
  <p>So I was wondering if there's a way in <code>IGListKit</code> to get the index of the currently visible cells. Thanks!</p>