title: Know if UICollectionView is scrolling
body: <p>Is there a way in iOS to know if a UICollectionView is scrolling or not?</p>
  
  <p>I want to know it because I'm loading in every UICollectionCell an image downloaded from the Web, but if the Collection View is big and I scroll until the end it starts downloading every image and if I change view I must wait that previous download, this slow down the app and is not cool, lol :D</p>
  
  <p>Thanks and sorry for my English ;)</p>