title: ios - How to prevent UICollectionview scrolling when new cell is added
body: <p>I have a messenger app, conversations are displayed in a <code>UICollectionview</code>.</p>
  
  <p>When a new message is received, a new item is added to bottom of the <code>collectionview</code>. Everything is ok when user has scrolled to the bottom of the view, but when user scrolls up (to older messages) and a new message is received, <code>collectionview</code> scrolls to the bottom a bit (about new message's size).
  I want to keep the <code>collectionview</code> position and prevent scrolling when a new message is received and <code>collectionview</code> updates. How should I do this?</p>