title: Resize UICollectionView cells after image inside has been downloaded
body: <p>I'm building a <code>UICollectionView</code> and my custom cells will contain two labels and one image.</p>
  
  <p>Each image is downloaded asynchronously so I don't know it's size until the download it's complete. 
  Once is downloaded, I want to adapt each cell to re-layout it's content and frame to fit in height the image just downloaded.</p>
  
  <p>As <code>UICollectionViewLayout</code>, I'm using <a href="https://github.com/chiahsien/CHTCollectionViewWaterfallLayout" rel="noreferrer">CHTCollectionViewWaterfallLayout</a></p>
  
  <p>To download the image asynchronously I'm using <a href="https://github.com/rs/SDWebImage" rel="noreferrer">SDWebImage</a>, like this:</p>
  
  <pre><code>    [cell.imageView setImageWithURL:[NSURL URLWithString:@"http://www.domain.com/path/to/image.jpg"]
                     placeholderImage:[UIImage imageNamed:@"placeholder.png"]
                            completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType) 
                                  {... some completion code here ...}];
  </code></pre>
  
  <p>QUESTION:</p>
  
  <p>What is the right approach to resize each <code>UICollectionViewCell</code> right after the image is downloaded?</p>