title: How to implement a NSCollectionView with centered items which have self-resizing margins?
body: <p>Suppose that I have one item in the collection view, the item will be centered in the collection view on the first row.</p>
  
  <p>And with multiple items, all these items will be distributed horizontally in the collection view with appropriate spacing between them.</p>
  
  <p>If the size of the collection view changed, the spacing between items will be changed simultaneously to fit the new size of the collection view.</p>
  
  <p>The default behavior of <code>NSCollectionView</code> aligns the items at the left, without spacing between multiple items.</p>
  
  <p>Should I use the <code>layoutManager</code> of collection view's layer to layout the items?</p>
  
  <p>Since I am using data binding to provide items, it seems not easy to insert the constraints. </p>