title: How to replace UICollectionViewDelegateFlowLayout by a reactive(RxSwift) call?
body: <p>Is there a way to replace the method </p>
  
  <pre><code>func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -&gt; CGSize
  </code></pre>
  
  <p>from the <code>UICollectionViewDelegateFlowLayout</code> protocol by something reactive using RxSwift? </p>