UITableView 中的行不会立即删除

Question

I'm using trailingSwipeActionsConfigurationForRowAt UITableView 's delegate method for handling when user swipe to delete certain cell (item).

My UIContextualAction for delete event looks like this. I first remove item from Realm database and then I delete row from my table view

func tableView(_ tableView: UITableView, trailingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
    let deleteAction = UIContextualAction(style: .destructive, title: nil) { _,_,_ in
        Repository.shared.deleteItem(self.items![indexPath.row])
        tableView.deleteRows(at: [indexPath], with: .fade)
    }
    ...
}

But from some reason when I delete cell, it isn't deleted immediately and it returns to position between swipe. Then when I scroll table view, cell disappeared like you can see in gif below:

I can "fix" this by reloading data of table view right after I remove certain item from database, but this is not what I want to, I want to use deleteRow(at:with:) because of animation.

---

One my guess is, that it has something to do with deleting item from Realm database.

I'm deleting item using delete method

func deleteItem(_ item: Item) {
    do {
        try realm.write {
            realm.delete(item)
        }
    } catch {
        print(error)
    }
}

then as data source array for my table view I'm using Realm's Results

var items: Results<Item>?

---

Does anybody have any idea why this happens? Thank you.

Answer 1

I was facing the exactly the issue you had. I'm using Realm too, and I also used Results<Item> as my tableView datasource.

My implementation for swipe-to-delete-cell in tableView(_:, trailingSwipeActionsConfigurationForRowAt:) method is exactly same as yours: delete the swiped item in realm.write{} block, then call UITableView.deleteRows(at:with:) method to update the tableView. There's no need to update the datasource items as Realm Results<T> auto updates itself.

All is working well on iOS 13 and above, but when I tested it on iOS 12.4, iPhone 6 simulator, I had the same issue as you described in the question.

I figured out a solution while reading this article , it turned out that all you need to do is to call the completion handler provided in UIContextualAction.Handler after you have finished your updates, please refer to the code below:

func tableView(_ tableView: UITableView, trailingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
    let deleteAction = UIContextualAction(style: .destructive, title: "Delete") { _, _, completion in
        Repository.shared.deleteItem(self.items![indexPath.row])  // delete item from Realm
        tableView.deleteRows(at: [indexPath], with: .fade)  // update tableView
        completion(true) // notify the tableView that the swipe action has completed so now it can perform UI updates (this line is no longer needed on iOS 13+)
    }
    ...
}

This solved my problem, hope it works for you too.