RLMException when using Realm through different view controllers - ios

Question

I am using Realm in swift to create a list of favorite products to be saved on the user's device.
In short, 2 views controllers (A and B) are embeded in a tab bar controller.
View controller A displays some products that are fetched from a Firebase database.
View controller A also has a "add to favorites" button that adds a product to a Realm instance.
View controller B embeds a table view to display the results from this Realm instance.
The problem is that when I delete some products from the table view, I get
the following error as soon as I go back to view controller A.
Terminating app due to uncaught exception 'RLMException', reason: 'Object has been deleted or invalidated
I have read that this error occurs when trying to access deleted objects from Realm, or when trying to re-add an object that was previously deleted. That doesn't seem to be the case here.
Thank you for any advice.
Here is the "add to favorite" button in my View Controller A:
#IBAction func addToFavorites(_ sender: Any) {
let realm = try! Realm()
try! realm.write {
realm.add(currentProduct)
}
}
Here is the table view code in my View Controller B:
class ViewControllerB: UIViewController, UITableViewDataSource, UITableViewDelegate {
let realm = try! Realm()
var favorites: Results<Product>!
#IBOutlet weak var favoritesTableView: UITableView!
override func viewDidLoad() {
super.viewDidLoad()
favoritesTableView.delegate = self
favoritesTableView.dataSource = self
favoritesTableView.rowHeight = 70
}
override func viewWillAppear(_ animated: Bool) {
favorites = realm.objects(Product.self)
favoritesTableView.reloadData()
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return favorites.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! favoriteTableViewCell
let product = favorites[indexPath.row]
cell.productName.text = product.name
cell.productCategory.text = product.category
return cell
}
func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCellEditingStyle, forRowAt indexPath: IndexPath) {
if editingStyle == .delete {
let product = favorites[indexPath.row]
try! realm.write {
realm.delete(product)
}
tableView.deleteRows(at: [indexPath], with: UITableViewRowAnimation.bottom)
}
}
EDIT:
Here is the full view controller A
import UIKit
import RealmSwift
class ViewControllerA: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
var products = [Product]()
var scannedProduct = Product()
var currentProduct = Product()
let realm = try! Realm()
#IBOutlet weak var myCollectionView: UICollectionView!
#IBAction func addToFavorites(_ sender: Any) {
try! realm.write {
realm.add(currentProduct)
}
}
override func viewDidLoad() {
super.viewDidLoad()
myCollectionView.delegate = self
myCollectionView.dataSource = self
myCollectionView.isPagingEnabled = true
myCollectionView.backgroundColor = UIColor.blue
layout()
}
override func viewDidAppear(_ animated: Bool) {
currentProduct = scannedProduct
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return products.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! collectionCell
cell.productName.text = products[indexPath.item].name
cell.codeLabel.text = products[indexPath.item].code
return cell
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize(width: myCollectionView.bounds.width, height: myCollectionView.bounds.height)
}
func layout() {
if let flowLayout = myCollectionView.collectionViewLayout as? UICollectionViewFlowLayout {
flowLayout.scrollDirection = .horizontal
flowLayout.minimumLineSpacing = 0
}
}
func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
let currentVisibleCell = myCollectionView.visibleCells.first
let currentIndex = myCollectionView.indexPath(for: currentVisibleCell!)?.item
currentProduct = products[currentIndex!]
}
}

Answer 1

when trying to access deleted objects from Realm, That doesn't seem to be the case here.
Actually...
try! realm.write {
realm.delete(product)
}
tableView.deleteRows(at: [indexPath], with: UITableViewRowAnimation.bottom)
These two lines shouldn't look like this. You see, Realm has this thing called a NotificationToken, and the ability to observe a results. According to the examples, it should look like this:
var notificationToken: NotificationToken?
override func viewDidLoad() {
...
// Set results notification block
self.notificationToken = results.observe { (changes: RealmCollectionChange) in
switch changes {
case .initial:
// Results are now populated and can be accessed without blocking the UI
self.tableView.reloadData()
break
case .update(_, let deletions, let insertions, let modifications):
// Query results have changed, so apply them to the TableView
self.tableView.beginUpdates()
self.tableView.insertRows(at: insertions.map { IndexPath(row: $0, section: 0) }, with: .automatic)
self.tableView.deleteRows(at: deletions.map { IndexPath(row: $0, section: 0) }, with: .automatic)
self.tableView.reloadRows(at: modifications.map { IndexPath(row: $0, section: 0) }, with: .automatic)
self.tableView.endUpdates()
break
case .error(let err): // this is probably not relevant in a non-sync scenario
break
}
}
If you have this, then you can theoretically just remove your own tableView.deleteRows(at: [indexPath], with: UITableViewRowAnimation.bottom) calls. This observer would keep the TableView up to date whenever a change occurs (write happens to Realm).