Insert rows in the top of UITableView without scrolling.

InsertRowsWithoutScrollingViewController.swift

import UIKit

final class ViewController: UITableViewController {

    private var names: [String] = (50...99).map { String($0) }

    override func viewDidLoad() {
        super.viewDidLoad()

        DispatchQueue.main.asyncAfter(deadline: .now() + 3.0) {
            self.appendCells()
        }
    }

    private func appendCells() {
        let oldContentHeight: CGFloat = tableView.contentSize.height
        let oldOffsetY: CGFloat = tableView.contentOffset.y
        names = (0...49).map { String($0) } + names
        tableView.reloadData()
        let newContentHeight: CGFloat = tableView.contentSize.height
        tableView.contentOffset.y = oldOffsetY + (newContentHeight - oldContentHeight)
    }

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

    override 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
    }
}