CollectionView layout on device rotation

layout.m

// Subclass UICollectionViewFlowLayout and overrite this method.
- (UICollectionViewLayoutInvalidationContext *)invalidationContextForBoundsChange:(CGRect)newBounds {
	UICollectionViewFlowLayoutInvalidationContext *context = (UICollectionViewFlowLayoutInvalidationContext *)[super invalidationContextForBoundsChange:newBounds];
	context.invalidateFlowLayoutDelegateMetrics = (
												   CGRectGetWidth(newBounds) != CGRectGetWidth(self.collectionView.bounds) ||
												   CGRectGetHeight(newBounds) != CGRectGetHeight(self.collectionView.bounds)
												   );
	return context;
}