issues with loaded UICollectionViewCells after reloadData() when layout.currentPage > layout.numberOfVisibleItems

[jlynch1]

I have 10 UICollectionViewCell (each with an image inserted) in UICollectionView, and initially due to restrictions on the rate of downloading images I had reduced the number of visible items to 5
layout.numberOfVisibleItems = 5

When I go to change my data model and do a full reload of the UICollectionView, depending on what UICollectionViewCell Im on....ie the value for layout.currentPage and layout.currentScrollOffset determines which 5 cells will be loaded in memory after the reloadData()....

.e.g. currentPage is 9, do a reloadData(), and cells 5,6,7,8,9 are loaded into memory. then I setCurrentPage() to 2

for the UICollectionViewCells 0 and 1 behind page 2, the images displayed are from the recycled UICollectionViewCell taken from memory like if they were cached - even though the new images have been downloaded again and set in the imageView in the UICollectionViewCell

Initially I was thinking:

• could be an issue between the reloadData() call and setCurrentPage() but these are both performed on the main thread.
• I played around with forcing invalidateLayout() before and after the reloadData()
• I was thinking if I should reset layout.currentPage before doing the reload.

DispatchQueue.main.async {
  self.carouselView.collectionViewLayout.invalidateLayout()
  self.carouselView.layoutIfNeeded()

  self.dataModel = newDataModel
  self.carouselView.reloadData()

  layout.setCurrentPage(index, animated: true)
}

But when I don't set layout.numberOfVisibleItems and leave it at the default, the issue with showing the wrong images behind the currentPage does not happen. There is also no need for invalidateLayout() here

So I am wondering if I'm missing something when using layout.numberOfVisibleItems or if there is a bug there

[amirdew]

Hi,
the way that you use numberOfVisibleItems seems okay, I think the issue is about invalidating, could you try invalidating layout via performBatchUpdates like this?

        collectionView.reloadData()
        collectionView.performBatchUpdates({
            self.collectionView.collectionViewLayout.invalidateLayout()
        })

if this didn't work, can you make a simple project and share it here, it's probably not related to downloadable images!
it might be a bug but I need to find a way to reproduce it.

[jlynch1]

Hi Amir,

Thanks for the response, I had tried the way you suggest... the same way as its done in viewDidLayoutSubviews() method but it had the same problems. By the way I was using the configuration for the inverted cylinder which I took from the mac layout designer app. I will look at creating a sample project to reproduce the issue.

Thanks
Jonathan

[amirdew]

Hi Jonathan,
With the new version the issue should be fixed, no need to call performBatchUpdates or invalidateLayout anymore,
Check the version 1.0.0 or higher and feel free to open a new ticket if needed