Failed to insert data into UITableView in swift

Question

I would like to insert a new data array into the UITableView without using reloadData() method.

I created simple code to do that. I referred to this discussion. However, error is occurred. I investigated why error is occurred, but I could not find it out.

My source code is here.

class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {

    @IBOutlet weak var tableView: UITableView!

    var objects = [
        "Apple",
        "Orange"
    ]

    let insertObjects = [
        "Banana",
        "Grape"
    ]

    override func viewDidLoad() {
        super.viewDidLoad()

        self.tableView.delegate = self
        self.tableView.dataSource = self

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }

    @IBAction func insert(_ sender: Any) {
        self.objects = self.insertObjects + self.objects
        tableView.beginUpdates()
        let indexPath = IndexPath(row: 0, section: 0)
        tableView.insertRows(at: [indexPath], with: .automatic)
        tableView.endUpdates()
    }


    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return self.objects.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = self.tableView.dequeueReusableCell(withIdentifier: "TableViewCell", for: indexPath) as! TableViewCell

        cell.label.text = self.objects[indexPath.row]
        return cell
    }
}

And, error message is here.

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid update: invalid number of rows in section 0.  The number of rows contained in an existing section after the update (4) must be equal to the number of rows contained in that section before the update (2), plus or minus the number of rows inserted or deleted from that section (1 inserted, 0 deleted) and plus or minus the number of rows moved into or out of that section (0 moved in, 0 moved out).'
*** First throw call stack:

Could give me your advice ?

You may have added multiple objects to your array in once. But you are just updating one indexPath. — ridvankucuk, Jan 09 '18 at 08:10

pacification · Answer 1 · 2018-01-09T08:46:58.530

1

You should rewrite this function like:

@IBAction func insert(_ sender: Any) {
    objects = insertObjects + objects
    let indexPaths = (0..<insertObjects.count).map({ IndexPath(row: $0, section: 0) })
    tableView.insertRows(at: indexPaths, with: .automatic)
}

Because the insertObjects has 2 elements, you need to reload two IndexPaths or just call tableView.reloadData() instead of begin/endUpdates code.

edited Jan 09 '18 at 08:46

answered Jan 09 '18 at 08:11

pacification

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What if insertObjects has more than 2 elements? – ridvankucuk Jan 09 '18 at 08:12
let indexPath3 = IndexPath(row: 2, section: 0) – Khawar Islam Jan 09 '18 at 08:13
What you want to achieve ? – Khawar Islam Jan 09 '18 at 08:14
`begin-/endUpdates` has no effect at all in this case. – vadian Jan 09 '18 at 08:34
@vadian, can't find any info about it. can explain why? – pacification Jan 09 '18 at 08:39
1

Look at the [documentation](https://developer.apple.com/documentation/uikit/uitableview/1614908-beginupdates): *Begins a series of method calls that insert, delete, or select rows and sections of the table view*. **series** mean **multiple** consecutive `insert/delete/move` lines. By the way your code crashes. – vadian Jan 09 '18 at 08:42

vadian · Answer 2 · 2018-01-09T08:38:05.527

When inserting new objects after the first reload you have to provide an IndexPath for each inserted object.

As the items are inserted at the beginning of the table this solution counts the number of new items and maps the indexes to IndexPaths

@IBAction func insert(_ sender: Any) {
    let numberOfItemsToInsert = self.insertObjects.count
    let indexPaths = (0..<numberOfItemsToInsert).map{IndexPath(row: $0, section: 0)}
    self.objects = self.insertObjects + self.objects
    tableView.insertRows(at: indexPaths, with: .automatic)
}

As always, begin-/endUpdates() is not needed for a single insert operation.

Failed to insert data into UITableView in swift

2 Answers2