Adjust content size of collection view when flexible iOS 8 simulator size changes

gistfile1.m

@interface UICollectionViewFlowLayout (InvalidateOnBoundsChange)
@end

@implementation UICollectionViewFlowLayout (InvalidateOnBoundsChange)

- (UICollectionViewLayoutInvalidationContext *)invalidationContextForBoundsChange:(CGRect)newBounds {
  UICollectionViewLayoutInvalidationContext *context = [super invalidationContextForBoundsChange:newBounds];
  
  CGRect oldBounds = self.collectionView.bounds;
  CGFloat widthAdjustment = newBounds.size.width - oldBounds.size.width;
  CGFloat heightAdjustment = newBounds.size.height - oldBounds.size.height;
  context.contentSizeAdjustment = CGSizeMake(widthAdjustment, heightAdjustment);
  return context;
}

@end