iOS: Invalid update: invalid number of rows in section n

Question

I am building an iOS app, basically the user create an item by pressing the "+" button and then the app should put the new item in according section of the table based on the location of the item. However I got the error: Invalid update: invalid number of rows in section 1. The number of rows contained in an existing section after the update (1) must be equal to the number of rows contained in that section before the update. Here is my code, thank you

let sections = ["Bathroom", "Bedroom", "Dining Room", "Garage", "Kitchen", "Living Room"]

@IBAction func addNewItem(_ sender: UIBarButtonItem) {
    /*
    //Make a new index path for the 0th section, last row
    let lastRow = tableView.numberOfRows(inSection: 0)
    let indexPath = IndexPath(row: lastRow, section: 0)

    //insert this new row into the table
    tableView.insertRows(at: [indexPath], with: .automatic)*/

    //Create a new item and add it to the store
    let newItem = itemStore.createItem()
    var Num: Int = 0

    if let index = itemStore.allItems.index(of: newItem) {
        switch newItem.room {
        case "Bathroom":
            Num = 0
            print("I am in here")
        case "Bedroom":
            Num = 1
        case "Dining Room":
            Num = 2
        case "Garage":
            Num = 3
        case "Kitchen":
            Num = 4
        case "Living Room":
            Num = 5
        default:
            Num = 0
            print("I am in Default")
        }
        let indexPath = IndexPath(row: index, section: Num)
        tableView.insertRows(at: [indexPath], with: .automatic)
    }

override func numberOfSections(in tableView: UITableView) -> Int {
    return sections.count
}

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

    return itemStore.allItems.count

}

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    //create an instance of UITableViewCell, with default appearance
    //let cell = UITableViewCell(style: .value, reuseIdentifier: "UITableViewCell")

    //get a new or recycled cell
    //if indexPath.row < itemStore.allItems.count {

        let cell = tableView.dequeueReusableCell(withIdentifier: "ItemCell", for: indexPath) as! ItemCell

        //Set the text on the cell with the decription of the item
        //that is at the nth index of items, where n = row this cell
        //will appear in on the table view
        let item = itemStore.allItems[indexPath.row]

        if item.name == "" {
            cell.nameLabel.text = "Name"
        } else {
            cell.nameLabel.text = item.name
        }

        if item.serialNumber == nil {
            cell.serialNumberLabel.text = "Serial Number"
        } else {
            cell.serialNumberLabel.text = item.serialNumber
        }
        cell.valueLabel.text = "$\(item.valueInDollars)"
        cell.roomLabel.text = item.room

        if item.valueInDollars < 50 {

            cell.valueLabel.textColor = UIColor.green

        }else if item.valueInDollars >= 50 {

            cell.valueLabel.textColor = UIColor.red
        }

        cell.backgroundColor = UIColor.clear
        return cell
}

override func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
    let LocationName = sections[section]
    return LocationName
}

thank you so much for your time!

and this is how I create item

 @discardableResult func createItem() -> Item {
    let newItem = Item(random: false)

    allItems.append(newItem)

    return newItem
}

Answer 1

The problem is that you should insert the item in the array first:

itemStore.allItems.append(newItem)

Also, there is a difference between sections and rows in numberOfRowsInSection(return number of rows for every section) you have a switch that returns the same number, it should be

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
     return itemStore.allItems.count
}

Edit :

The problem is when the table loads there is 0 rows for all the sections ( itemStore.allItems.count is zero ), when you try to insert a row say at section 0 , row 0 -- the dataSource must be updated only for that section , which is not happen in your case as it's the same array that is returned for all sections , so you must either have an array of array where inner array represent number of rows so addition/deletion from it doesn't affect other ones ,,,,, or lock the insert to say section 0 like this

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

   if (section  == 0 ) { 
       return itemStore.allItems.count
   }
   return 0 
}

in this edit i inserted in 2 sections 0 and 2 with no crash because i handled numberOfRowsInSection to return old numbers for old section that why to be able to insert in all sections you must have a different data source array or manage from numberOfRowsInSection , see edited demo here Homepwner

Instead of setting footer in viewDidLoad implement this method

override func tableView(_ tableView: UITableView, viewForFooterInSection section: Int) -> UIView? {

    if(section == 5 ) {
        let textLabel = UILabel()
        textLabel.text = "No more Item"
        return textLabel
    }

    return nil
}

Answer 2

@Jacky.S I downloads your code and try to debug it.Fist look our error properly.

reason: 'Invalid update: invalid number of rows in section 1.  The number of rows contained in an existing section after the update (1) must be equal to the number of rows contained in that section before the update (0)

So It says before update, your sections has 0 rows. Now you try to update you tableview using this piece of code.

print(indexPath)
tableView.insertRows(at: [indexPath], with: .automatic)

I just added the print statement for debugging purpose and it prints [0, 0] .So you say your tableview to insert 0th row on section 0. Now when you insert any row into tableview it calls the delegate method.Now look at the below delegate method.

override func tableView(_ tableView: UITableView, numberOfRowsInSection 
  section: Int) -> Int {
    if section == 0{
        print("0",itemStore.allItems.count)
    }
    if section == 1{
        print("1",itemStore.allItems.count)
    }
   // print(itemStore.allItems)
        return itemStore.allItems.count
}

In your code you just return itemStore.allItems.count.I added the above code for debugging.Now look that itemStore.allItems.count always return 1.So for first section it works perfectly because few times ago you insert a row in first section whose index is [0 = row, 0 = section].So you previously returned rows for section 0 is equal to the recently return rows for section 0.But When it comes for section 1 you previously return no row that means your section 1 has no rows in previous but in your above delegate method you also return 1 row for section 1.Which is conflicting because in previous you never update or return any rows for section 1.That's why you code crash and and say that

your number of rows contained in an existing section after the update is 1 which must be equal to the number of rows contained in that section before the update. Which is 0.

So this is the explanation for you crash.

Now, to recover from crash your allItems should be a dictionary or an array of array.

var allItems = [[Item]]()

or

var allItems = ["String":[Item]]()

guess allItems element is something like this

allItems = ["bathroom":[item1, item2, item3],"bedroom":[item1, item2, item3, item4]]

so here you have 2 section one is bathroom and another is bedroom.First section have 3 row and second one have 4 row and in you tableview delegate method you have to return 3 for section 0 and 4 for section 1

Answer 3

There is something terribly wrong with your data source. Your numberOfRow for all sections is the same. i.e. itemStore.allItems.count. Which means you are setting the same number of rows in each section.
The main issue is, while adding a new item, you are inserting a new row in the specific section which means

new number of rows for section = previous number of rows in section + 1

However, there is no addition in the data source.

So according to the code, you have inserted a new row, but your data source has one record less since you didn't add the item there.

So I would like you do the following in order of these steps :

1. Add item in required data source.
2. inserRowInSection

Update : Remove the condition in cellForRowAtIndexPath :

if indexPath.section <= 1 and it's else block. You don't need that. If number of sections is less than 1, it won't be called. Moreover it's the else block which is getting called all the time because you already have sections in your code. So if case will never be called.

So I got the issue. In itemStore.createItem() the value for room is always Room. In the switch-case, you never have Room case. So it always falls in default case. You need to fix that.