title: UICollectionView cell disappears when i scroll it
body: <p>I have a collectionView whose scroll direction is horizontal. It has only one line and its cell spacing is 16.0px. So i set its <code>collectionViewLayout</code> to a custom layout named <code>UICollectionViewLeftAlignedLayout</code> subclass of <code>UICollectionViewFlowLayout</code>:  </p>
  
  <pre><code>UICollectionViewLeftAlignedLayout *layout     = [[UICollectionViewLeftAlignedLayout alloc] init];
  layout.scrollDirection                        = UICollectionViewScrollDirectionHorizontal;
  layout.minimumInteritemSpacing                = 16.0;
  _myCollectionView.collectionViewLayout        = layout;  
  _myCollectionView.autoresizingMask            = UIViewAutoresizingFlexibleWidth|UIViewAutoresizingFlexibleHeight;
  </code></pre>
  
  <p>But when i scroll the collectionView, some cells of it disappeared. So weird! I have tried every solution i can find from <code>google.com</code>, unfortunately did not work for me. I fix it and post the solution as a answer below.</p>