UICollectionView wrong contentSize on first load, correct after that

Question

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.

i'm sure it's something to do with autolayout.. try disabling it — abbood, Aug 16 '13 at 08:08
Already disabled, first thing I thought too. It seems like it's not loading the view fast enough, because on reappearance the width is correct (for ex. when coming back to the same view). — klauslanza, Aug 17 '13 at 08:29
Stumbled upon a similar bug with different project on iOS 7. This time I get incorrect inset on first load after installing the app. All subsequent loading of the collection are correct. Can't find the right way to start finding a solution ... — klauslanza, Jun 25 '15 at 16:21

score 71 · Accepted Answer · edited May 23 '17 at 12:34

71

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.

edited May 23 '17 at 12:34

Community

1
1

answered Aug 04 '15 at 05:52

ucangetit

2,595
27
21

You saved my life. :D Thank you so so much. @ucangetit – iPeter May 31 '17 at 19:45
I find my collectionView.contentSize.height is larger than the max result of `contentOffset.y`, even with `[self.collectionView layoutIfNeeded]`. – wzso Mar 11 '19 at 08:41
2

this didn't work for me. I'm using `layout.estimatedItemSize = CGSize(width: 1, height: 1)` and it returns 1, 1 even after calling self.collectionView.layoutIfNeeded – osrl Mar 22 '19 at 10:59
1

@osrl make sure you set your `estimatedItemSize` close to your actual size of your cells. This property is just a starting point for the system to size your cells with, if your cells are all wildly different sizes, then it's best to start with a size of your smallest cell IMHO. – ucangetit Aug 25 '19 at 14:56

score 3 · Answer 2 · answered Jun 17 '20 at 11:08

In my case, I was always getting content size zero. layoutIfNeeded() was not enough for me I have to get content size inside DispatchQueue.main.async ie

    self.collectionView.layoutIfNeeded()
    DispatchQueue.main.async {
        print(self.collectionView.contentSize) 
    }

score 0 · Answer 3 · answered Feb 07 '20 at 11:07

Above answer is correct, but if you are adding the UICollectionViewController programmatically or with xib/storyboard, we have to take care about the scrollDirection of the UICollectionViewFlowLayout() for the UICollectionViewController. If it is horizontal and you want to track the content height, then there is a strong possibility that you will not get proper results.

In my case I used below code.

self.someCollectionViewController?.collectionView.reloadData()
self.someCollectionViewController?.collectionView.layoutIfNeeded()
if let height = self.someCollectionViewController?.collectionViewLayout.collectionViewContentSize.height {

   self.someProductCollectionViewHeightConstraints?.constant = height
}

score 0 · Answer 4 · answered Mar 27 '23 at 09:35

0

I got the same mistake ,and I resolve this by layout.estimatedItemSize = CGSizeMake(CGFLOAT_MIN, 24), height 24 is which I wanted height, the item's width is I want to auto calcullated

answered Mar 27 '23 at 09:35

Flappy_Fan

1

UICollectionView wrong contentSize on first load, correct after that

4 Answers4