I have a common UICollectionView with paging and all.
Still trying to figure out why on viewDidLoad:, viewWillAppear: and viewDidAppear: , only on first view call, I get the wrong size when calling myCollectionView.collectionView.contentSize.width. It always respond with 0 width (height is always correct). Successive reload of the view get me the correct one.
Resorted to using
self.collectionView.collectionViewLayout.collectionViewContentSize
which give me the correct width event on first load.
Still a mystery to me.
So I was seeing a similar issue where contentSize width was always zero. The simple answer is...there is probably no content in the collectionView yet. That was why it's content size is zero.
I was also noticing that sometimes after calling invalidateLayout on my UICollectionView, I was seeing that self.collectionView.collectionViewLayout.collectionViewContentSize was not the same as self.collectionView.contentSize.
After much searching I found a great hint here in this SO post
What I needed to do to get both contentSize calculations to be the same was to call [self.collectionView layoutIfNeeded] immediately after calling [self.collectionView reloadData] or [self.collectionView.collectionViewLayout invalidateLayout].
This essentially forces the reload to happen immediately instead of on the next runloop cycle.
I really hope this solves your issue.