title: UICollectionView showing wrong cells after scrolling - dequeue issue?
body: <p>I have a UICollectionView within a UIViewController. In the collectionView cellForItemAtIndexPath: method, it creates a series of custom cells based on the datasource. The custom cells in turn contain a UIView, subclassed to draw single PDF pages. </p>
  
  <p>It's set up in such a way as to split a PDF file into its single pages, so cell 1 contains PDF page 1, cell 2 contains PDF page 2 and so on. So far so good, here's my problem:</p>
  
  <p>When I scroll down, the UICollectionView starts displaying the wrong cells. For instance in a 34 page document, it shows cells/pages 1-16 in the correct order, but then starts displaying pages that <em>seemed</em> to have been dequeued further up, such as cell 1, cell 2, cell 4. I never get anywhere near cell/page 34. </p>
  
  <p>I've seen similar behaviour from UITableView in the past, and believe it has something to do with the dequeueing of the cells, or a delegate method. Not quite sure - any help is appreciated. </p>
  
  <pre><code>- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
  
  //create custom cell
  CustomCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"cellID" forIndexPath:indexPath];
  
  //set file name (always the same; one PDF file)
  cell.fileName = fileName;
  cell.backgroundColor = [UIColor clearColor];
  
  //set the title to the page number
  cell.title = [NSString stringWithFormat:@"page %@", [countArray objectAtIndex:indexPath.row]];
  
  //set the current page (which indicates which page to display) according to the pageCount
  cell.currentPage = [[countArray objectAtIndex:indexPath.row] intValue];
  
  return cell; }
  </code></pre>