title: targetContentOffsetForProposedContentOffset:withScrollingVelocity without subclassing UICollectionViewFlowLayout
body: <p>I've got a very simple collectionView in my app (just a single row of square thumbnail images).</p>
  
  <p>I'd like to intercept the scrolling so that the offset always leaves a full image at the left side.  At the moment it scrolls to wherever and will leave cut off images.</p>
  
  <p>Anyway, I know I need to use the function</p>
  
  <pre><code>- (CGPoint)targetContentOffsetForProposedContentOffset:withScrollingVelocity
  </code></pre>
  
  <p>to do this but I'm just using a standard <code>UICollectionViewFlowLayout</code>. I'm not subclassing it.</p>
  
  <p>Is there any way of intercepting this without subclassing <code>UICollectionViewFlowLayout</code>?</p>
  
  <p>Thanks</p>