title: UICollectionView horizontal flow layout: how to make cells go left-right top-down?
body: <p>I'm using UICollectionView with different sections, the problem is within a section if there are not enough item, the only items are centred, is there a way to make it layout cells to be from left to right and top to bottom? Without adding transparent placeholder cells?
  Thanks</p>
  
  <p>edit:</p>
  
  <p>Screen shot added, so section 1 has the big orange bar and two small green bars, the one on the right of big orange bar should be in section 1, so I want it to be below the big orange bar, next to another green bar which is already there.</p>
  
  <p>Also, say if section 1 has only 1 big orange bar, I want it to be top aligned, but it is centered.</p>
  
  <p><img src="https://i.stack.imgur.com/kRslU.png" alt="Screenshot"></p>