retain scroll position for nested collectionView - ios

Question

After the tableView.reloadData() the visible collectionView display the first row unexpected immediately.
Im building a tableView contains collectionView in its cells, users can scroll multiple images in every single tableView just like Instagram. How can I fix it? Thanks!
tableView DataSource
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return photoRolls.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "tableViewCell", for: indexPath) as! HomeTableViewCell
if photoRolls.isEmpty {
return UITableViewCell()
}
let user: UserModel = users[indexPath.row]
let photoRoll: PhotoRoll = photoRolls[indexPath.row] //this Model contains post info: likes, comments etc.
let photoUrls: UrlStrings = urls[indexPath.row] //this Model contains a array of urlStrings for each collectionView inside the tableViewCell
cell.urlStrings = photoUrls
cell.photoRoll = photoRoll
cell.user = user
cell.delegate = self
return cell
}
prepareForReuse Method in tableViewCell
override func prepareForReuse() {
super.prepareForReuse()
captionLabel.text = nil
profileImage.image = UIImage(named: "placeholderImg")
profileImageRight.image = UIImage(named: "placeholderImg")
collectionView.scrollToItem(at:IndexPath(item: 0, section: 0), at: .left, animated: false)//tried to remove this method, but the collectionView would not display the first row when it's visible
}
DataSource of collectionView inside tableViewCell
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return cellUrlArray.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "HomeCollectionViewCell", for: indexPath) as! HomeCollectionViewCell
cell.url = cellUrlArray[indexPath.row]
return cell
}
Like the question title said. I expect the visible collectionView stays on the current row after the tableView load more data after tableView.reloadData() is called! Thanks again!

Answer 1

I think it is possible with contentOffset cacheing, like below
var cachedPosition = Dictionary<IndexPath,CGPoint>()
func tableView(_ tableView: UITableView, didEndDisplaying cell: UITableViewCell, forRowAt indexPath: IndexPath) {
if let cell = cell as? HomeTableViewCell {
cachedPosition[indexPath] = cell.collectionView.contentOffset
}
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
<<Your Code>>
cell.collectionView.contentOffset = cachedPosition[indexPath] ?? .zero
return cell
}