尝试插入行时“尝试将第 0 行插入第 0 节，但更新后第 0 节中只有 0 行”

Question

I'm using a UIViewController with a UITableView connected to another UIViewController where I intend to be able to add entries from. They are linked through an unwind segue, but whenever I try to actually add an entry, I get this:

attempt to insert row 0 into section 0, but there are only 0 rows in section 0 after the update

This is what I have:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

    super.prepare(for: segue, sender: sender)

    switch(segue.identifier ?? "") {

        case "AddItem":

        os_log("Adding a new item.", log: OSLog.default, type: .debug)

        case "ShowDetail":

            guard let DetailViewController = segue.destination as? ViewController else {

                fatalError("Unexpected destination: \(segue.destination)")
        }

            guard let selectedCell = sender as? TableViewCell else {

                fatalError("Unexpected sender: \(sender)")
        }

            guard let indexPath = tableView.indexPath(for: selectedCell) else {

                fatalError("The selected cell is not being displayed by the table")
        }

            let selectedItem = items[indexPath.row]

            DetailViewController.item = selectedItem

    default:

        fatalError("Unexpected Segue Identifier; \(segue.identifier)")
    }
}

and

@IBAction func unwindToList(sender: UIStoryboardSegue) {

    if let sourceViewController = sender.source as? ViewController, let item = sourceViewController.item {

        if let selectedIndexPath = tableView.indexPathForSelectedRow {

            items[selectedIndexPath.row] = item

            self.tableView.reloadRows(at: [selectedIndexPath], with: .none)

        }

        else {

            items.append(item)

            self.tableView.beginUpdates()

            self.tableView.insertRows(at: [IndexPath(row: items.count - 1, section: 0)], with: .automatic)

            self.tableView.endUpdates()

        }
    }
}

and

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

    return items.count

}

and

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

    let cellIdentifier = "TableViewCell"

    guard let cell = tableView.dequeueReusableCell(withIdentifier: cellIdentifier, for: indexPath) as? TableViewCell else {

        fatalError("The dequeued cell is not an instance of TableViewCell")

    }

    let item = items[indexPath.row]

    cell.labelName.text = item.name

    return cell

}

How can this be fixed?

And forgive me, I am fairly new to Swift. :)

Answer 1

If you want to use insertRowsAtIndexPaths:withRowAnimation: you need to do it inside a beginUpdates and endUpdates block, after updating your data array. According to Documentation :

To insert and delete a group of rows and sections in a table view, first prepare the array (or arrays) that are the source of data for the sections and rows. After rows and sections are deleted and inserted, the resulting rows and sections are populated from this data store.

You are doing correctly by changing the array before calling insertRowsAtIndexPaths:withRowAnimation: but you need to use batch updates instead of reloadData .

There is a complete example at the Documentation link that you can check.

Answer 2

Make sure the TableView's dataSource is connected (when using a storyboard or nib) or assigned programmatically. These errors also arise when trying to update a TableView or CollectionView with no dataSource assigned.