Override NSCollectionView item size
<p>So I have a collection view rendering with sections and items. I am using flowLayout and set the default item size like so:</p>

<pre><code>flowLayout.itemSize = NSSize(width: 64.0, height: 128.0)
</code></pre>

<p>According to the documentation, "...The collection view’s delegate can override the default size values and specify different values for each item."</p>

<p>How do I do this?</p>