Inserting Rows crashes in Swift - swift

Question

I am facing crash while inserting cells in TableView. I have tried below links but not sure what is the issue
Link1 Link2 Link3 and many
Below is my code
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return names.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell: UITableViewCell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
cell.textLabel?.text = names[indexPath.row]
return cell
}
Data Source code is below
private var names: [String] = (50...99).map { String($0) }
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
DispatchQueue.main.asyncAfter(deadline: .now() + 3.0) {
self.appendCells()
}
}
private func appendCells() {
names = (0...49).map { String($0) } + names
customTableView.beginUpdates()
let indexPat = IndexPath(row: names.count - 1, section: 0)
customTableView.insertRows(at: [indexPat], with: .fade)
customTableView.endUpdates()
}
I cant understand what am I missing here. Sorry if I am doing foolish. Please let me know If I have to explain more.
I am getting error :
reason: 'Invalid update: invalid number of rows in section 0. The number of rows contained in an existing section after the update (100) must be equal to the number of rows contained in that section before the update (50),

Answer 1

The problem is the mismatch in the number of values you add to the data model and the number of rows you add to the table view.
The line:
names = (0...49).map { String($0) } + names
adds 50 new values to your data model.
But you then only tell the table view that there is one new row. This is what you are being told in the error message.
You need a loop to build up an array of 50 index paths.
private func appendCells() {
names = (0...49).map { String($0) } + names
var paths = [IndexPath]()
for row in 0...49 {
let indexPath = IndexPath(row: row, section: 0)
paths.append(indexPath)
}
customTableView.insertRows(at: paths, with: .fade)
}

Answer 2

The error clearly states that you are adding indexPath with row = 99, section = 0, while in reality, it's biggest indexpath holds values: row = 49, section = 0.
Before insertion, tableview calls datasource method numberOfRowsInSection - this method must return your newer, bigger array count (100), not the earlier one (50).

Answer 3

1) Your model before ‘appendCells’ has 50 names count.
2) After call your mode is equal 100 names count but you only instert one cell at index path = 99? You need to insert 50 more rows instead of one.

Answer 4

I was having this problem, and it worked with the following approach
func insertRow(entries: [String]) {
tableView.performBatchUpdates({
self.tableView.insertRows(at: [IndexPath(row: entries.count - 1, section: 0)], with: .bottom)
}, completion: nil)
}