title: UICollectionView stick to a cell even if it's content offset may change
body: <p>This is a hard one, I hope I can explain it properly. </p>
  
  <p>All right, so the thing is that I have a <strong>UICollectionView</strong> where the <strong>height of the cell is dynamically changing</strong> using <code>collectionView.collectionViewLayout.invalidateLayout()</code> which guides into the <code>sizeForItemAtIndexPath()</code> method of UICollectionVieFlowLayout.</p>
  
  <p>This works perfectly. There is new content, it resizes, moves the other cells according to it, etc. Now, my collection view's content size is probably pretty big, that means when I'm stopping at cell number, say, 23, and cell number 15 is not even displayed but is changing it's size, it is going to make my cell number 23 move up or down. Can I kind of throw an "anchor" to where I currently am? Here's the code that's resizing the cell, triggered by Firebase:</p>
  
  <pre><code>            cell.resizeToText(text: text!)
  
              let size = CGSize(width: self.view.frame.width, height: cell.mainView.frame.height + (cell.mainView.frame.origin.y*2.5))
              let invalidationIndex = indexPath.row + 1
              self.invalidationSizeDictionary[invalidationIndex] = size
  
              let context = UICollectionViewLayoutInvalidationContext()
              context.invalidateItems(at: [indexPath])
  
              self.feedCollectionView.collectionViewLayout.invalidateLayout()
  </code></pre>
  
  <p><strong>Question:</strong> is there a possibility to stay at my current offset position in the collectionView?</p>