How to reload the indexPath of the collectionviewCell in Swift? - ios

Question

I'm currently working on an app that has a table-view-like collection view and some other view controllers. Basically, my question is how can I update the indexPath of each cell when one of the collection view cells is deleted.
I attached my view controller file below, but here is what's going on on the app.
When a user opens the table-view-like collection view (in EventCollectionVC), it reloads the data from a database and presents them on the collection view. I also added the code to the navigation bar button item that the user can change the collection view to the edit mode. While in the edit mode, a small ellipsis.circle (SF symbols) is displayed on the collection view cell. When a user taps the ellipsis.circle icon, it displays a new view controller (ModalVC) and lets the user select either delete or edit the cell. When the user selects delete, it shows an alert to delete the cell and delete the cell information with modal dismiss (which means the ModalVC is closed and the MyCollectionVC is displayed now).
Since I have to make the two view controllers (like getting cell information from EventCollectionVC and present in ModalVC) talk to each other, I need to use the indexPath.row to get the information of the cell. Before deleting the cells, the numbers of indexPath.row in the collection view is like
[0,1,2,3,4,5]
But, for example, after I delete the second (indexPath.row = 1) cell and when I try to delete another item, the indexPath becomes
[0,2,3,4,5]
and I can see the collection view's index is not refreshed.
So my question is how can I update/refresh the cell's indexPath.row value after I delete a cell from the collection view?
This is the code with some explanations.
import UIKit
class EvnetCollectionViewController: UIViewController {
var EventDataSource: EventDataSource! // <- this is a class for the Model, and it stores array or Events
let ListView = ListView() // view file
var collectionViewDataSource: UICollectionViewDiffableDataSource<Section, Event>?
var targetEventIndex = Int() // variable to store the index of the event when event cell is tapped
override func loadView() {
view = ListView
}
override func viewDidLoad() {
super.viewDidLoad()
configureNavItem()
setupCollectionView()
displayEvents()
}
func configureNavItem() {
navigationItem.rightBarButtonItem = editButtonItem
}
override func setEditing(_ editing: Bool, animated: Bool) {
super.setEditing(editing, animated: animated)
if (editing){
ListView.collectionView.isEditing = true
} else {
ListView.collectionView.isEditing = false
}
}
func setupCollectionView() {
let cellRegistration = UICollectionView.CellRegistration<UICollectionViewListCell, Event> { cell, indexPath, Event in
var content = UIListContentConfiguration.cell()
content.text = Event.title
cell.contentConfiguration = content
let moreAction = UIAction(image: UIImage(systemName: "ellipsis.circle"),
handler: { _ in
let vc = EventActionModalViewController(); // when the user select the cell in edit mode, it displays action modal VC and then come back to this VC with dismiss later
vc.modalPresentationStyle = .overCurrentContext
self.targetEventIndex = indexPath.row　// I need targetEvemtIndex when user selects delete event in EventActionModalVC, so just sotre value in here
})
let moreActionButton = UIButton(primaryAction: moreAction)
let moreActionAccessory = UICellAccessory.CustomViewConfiguration(
customView: moreActionButton,
placement: .trailing(displayed: .whenEditing, at: { _ in return 0 })
)
cell.accessories = [
.disclosureIndicator(displayed: .whenNotEditing),
.customView(configuration: moreActionAccessory)
]
}
collectionViewDataSource = UICollectionViewDiffableDataSource<Section, Event>(collectionView: ListView.collectionView) {
collectionView, indexPath, Event in
collectionView.dequeueConfiguredReusableCell(using: cellRegistration, for: indexPath, item: Event)
}
}
func displayEvents() {
EventDataSource = EventDataSource()
EventDataSource.loadData() // get Events in db and sore in an array Events
populate(with: EventDataSource.Events)
}
func populate(with Events: [Event]) {
var snapshot = NSDiffableDataSourceSnapshot<Section, Event>()
snapshot.appendSections([.List])
snapshot.appendItems(Events)
collectionViewDataSource?.apply(snapshot)
}
func showDeleteAlert() {
let deleteAction = UIAlertAction(title: "Delete", style: .destructive) { _ in
self.EventDataSource.delete(at: targetEventIndex)
self.refreshList()
}
let cancelAction = UIAlertAction(title: "Cancel", style: .cancel)
self.showAlert(title: "Delete", message: nil, actions: [deleteAction, cancelAction], style: .actionSheet, completion: nil)
}
func refreshList() {
EventDataSource.loadData()
setupCollectionView() // since I write this code, it updates all of the indexPath in the collection view, but after deleting one item, the whole collection view is deleted and new collection view is reappeared.
populate(with: EventDataSource.Events)
}
}
I kinda know why this is happening. I only configure cell (in let cellRegistration = UICollectionView.CellRegistration<UICollectionViewListCell, Event>...) once, so it won't update the cell information as well as its index path until I configure it again. But if I call setupCollectionView every after deleting one item, the whole collection view disappears and shows up again. Is it possible to reload the collection view list and updates its information without reloading the entire collection view?
Without writing setupCollectionView() in refreshList, the cell's indexPath is not refreshed and I get an error after I delete one cell and try to delete another one. So, I was wondering if there is a way to avoid recreating the whole collection view but update cells' indexPath when the user delete one of the cell in collection view.

Answer 1

I fixed the code in the refresh list function.
func refreshList() {
self.EventDataSource.loadData()
self.populate(with: self.EventDataSource.Events)
ListView.collectionView.reloadData()
}
I just needed to call reloadData after I populate all the data...