How to Override ScrollViewDidEndDecelerating and find current visible cell ? - ios

Question

I have a view controller which contains a collectionView:
class TagViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource {
#IBOutlet weak var collectionView: UICollectionView!
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return posts.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let post = posts[indexPath.row]
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! SNPostViewCell
cell.isVideo = post.isVideo
cell.mediaURL = URL(string: post.mediaURL)
cell.backgroundColor = UIColor.black
return cell
}
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let post = posts[indexPath.row]
if post.isVideo == true {
self.performSegue(withIdentifier: "playVideo", sender: nil)
} else {
print("is image. might go full screen one day here")
}
let bin = self.bins[post.timeStamp]
print(bin)
}
override func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) { //Error: method cannot override from its superclass
<#code#>
}
}
Although I can override those collectionView functions, it seems that to override scrollViewDidEndDecelerating I specifically need to have an instance of collectionView (and not do it in a view controller)
OK so I made a custom collectionView which inherits from collectionViewController. This overrides scrollViewDidEndDecelerating correctly (the method now DOES override from its superclass), and I am using code inside of it to find the index of the current cell,
class PagingCollectionViewController: UICollectionViewController {
...
override func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
if (self.collectionView.contentOffset.y < 0) {
self.collectionView.contentOffset = CGPointMake(self.collectionView.contentOffset.x, 0.0);
}
for cell in yourCollectionViewname.visibleCells() as [UICollectionViewCell] {
let indexPath = yourCollectionViewname.indexPathForCell(cell as UICollectionViewCell)
}
}
...
}
However, as you can see this needs to reference the current index of the collectionView which I wouldn't have defined in the class right? Only in the view Controller where the instance is created and populated...
So I don't really understand where to put this override scrollViewDidEndDecelerating function and how to access the data within it successfully - to find the index.

Answer 1

This is wrong:
override func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
<#code#>
}
... because scrollViewDidEndDecelerating is not an override method. It is a delegate method.
https://developer.apple.com/documentation/uikit/uiscrollviewdelegate/1619417-scrollviewdidenddecelerating
So delete the word override, and set self as the delegate of the collectionView, and you're all set.