如何重写ScrollViewDidEndDecelerating并找到当前可见的单元格？

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.