CollectionView with infinite horizontal scrolling in both directions and pagination enabled - ios

Question

I'm trying to create a view showing the dates for all weekdays in one single row with horizontal scrolling and pagination enabled. Similar to how it works in the iPhone's calendar app, one full week should be visible at once.
To do that, I created a collectionView and set it up to display those seven items. When the user scrolls to the left (to see the next week), the function collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) is called. Here I add the next items and reload the collectionView.:
func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
if indexPath.item > numberofitems - 10 {
numberofitems += 15
DispatchQueue.main.async {
self.myCollectionView.reloadData()
}
}
The collectionView is then reloaded:
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath) as! myCollectionViewCell
dayComponent.day = -3 * 7 - Calendar.current.component(.weekday, from: Date()) + indexPath.item + 1 + indecesadded
cell.setup(date: Calendar.current.date(byAdding: dayComponent, to: Date())!)
}
This seems to work pretty well.
However, what I also need, is being able to scroll in the other direction (backwards) and add new cells before the visible ones. I tried using the same method and adding the contentOffset:
func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
if indexPath.item < 10 {
numberofitems += 14
indecesadded += 14
DispatchQueue.main.async {
self.myCollectionView.reloadData()
self.myyCollectionView.setContentOffset(CGPoint(x: self.myCollectionView.contentOffset.x + 2 * self.view.bounds.width, y: 0), animated: false)
}
}
}
The problem is that after adding the new cells (mid-scrolling), the scrolling stops abruptly. When I manually beginn scrolling again, the paging seems to be off, meaning that the last day of one week does not correspond to the first day of the next - 1. (see images below).
before scrolling to previous week:
after scrolling:
after manually scrolling collectionView again:
So the question is: How do I insert items before the currently existing cells in a collectionView with paging enabled without messing up the scrolling and paging?

Answer 1

maybe you should try using scrollViewDidScroll like:
func scrollViewDidScroll(_ scrollView: UIScrollView) {
let offset = scrollView.contentOffset
lastContentOffset = offset //save the offset if u need to set it later
if offset.x > 30{
print("right")
scrollRight()
} else if offset.x < -30 {
scrollLeft() // here you can implement the code bellow preformBatchUpdates
print("left")
}
}
if you want to have a sort of jumpy experience, like when u scroll it turns the page but it doesn't show how the numbers smoothly go away like on built in IOS Calendar on IPhone, that's the code i've tried for that:
collectionView.performBatchUpdates(
{
collectionView.insertSections([0])
sectionIndex += 1
}, completion: nil)
collectionView.performBatchUpdates({
collectionView.deleteSections([sectionIndex - 1])
sectionIndex -= 1
}, completion: nil)
that is implied when i override scrollViewDidScroll and scroll left for example. same is done for the other direction, the idea is that you keep maintaining only 1 section, so the adding of the sections doesn't mess up the position of the items in collectionView. i am actually working on the same project so if someone could provide a sample code for how i can be done like on the IPhone calendar it would also help me, hope that snippet gives you any new ideas or solves your problem
the answer here here works but i get some weird results