1// This causes jumpy scrolling with dynamic cells
2tableView.estimatedRowHeight = 44  // Estimate is 44pt
3// But actual cells are 120pt, 80pt, 200pt — estimates are way off
4tableView.reloadData()  // Content jumps!

1class ViewController: UIViewController, UITableViewDelegate {
2
3    var cellHeightCache: [IndexPath: CGFloat] = [:]
4
5    func tableView(_ tableView: UITableView,
6                   willDisplay cell: UITableViewCell,
7                   forRowAt indexPath: IndexPath) {
8        // Cache the actual height after the cell is laid out
9        cellHeightCache[indexPath] = cell.frame.height
10    }
11
12    func tableView(_ tableView: UITableView,
13                   estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
14        // Return cached height if available, otherwise use a default estimate
15        return cellHeightCache[indexPath] ?? 100
16    }
17}

1// Instead of:
2// tableView.reloadData()
3
4// Use targeted updates:
5tableView.performBatchUpdates {
6    tableView.insertRows(at: [IndexPath(row: 0, section: 0)], with: .automatic)
7}
8
9// Or reload specific rows:
10tableView.reloadRows(at: [indexPath], with: .none)
11
12// Or reload a section:
13tableView.reloadSections(IndexSet(integer: 0), with: .none)

1let contentOffset = tableView.contentOffset
2tableView.reloadData()
3tableView.layoutIfNeeded()
4tableView.setContentOffset(contentOffset, animated: false)

1var dataSource: UITableViewDiffableDataSource<Section, Item>!
2
3func updateData(_ items: [Item]) {
4    var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
5    snapshot.appendSections([.main])
6    snapshot.appendItems(items, toSection: .main)
7
8    // Applies only the diff — no jumps
9    dataSource.apply(snapshot, animatingDifferences: true)
10}

1// Bad: default estimate for all cells
2tableView.estimatedRowHeight = 44
3
4// Better: estimate based on your typical cell content
5tableView.estimatedRowHeight = 120  // Closer to average actual height
6
7// Best: implement the delegate method with per-cell estimates
8func tableView(_ tableView: UITableView,
9               estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
10    let item = items[indexPath.row]
11    if item.hasImage {
12        return 250
13    } else if item.text.count > 200 {
14        return 150
15    }
16    return 80
17}

tableView.estimatedRowHeight = 0
tableView.estimatedSectionHeaderHeight = 0
tableView.estimatedSectionFooterHeight = 0

1class FeedViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {
2
3    @IBOutlet weak var tableView: UITableView!
4    var items: [FeedItem] = []
5    var heightCache: [IndexPath: CGFloat] = [:]
6
7    override func viewDidLoad() {
8        super.viewDidLoad()
9        tableView.delegate = self
10        tableView.dataSource = self
11        tableView.rowHeight = UITableView.automaticDimension
12        tableView.estimatedRowHeight = 120
13    }
14
15    // MARK: - Height Caching
16
17    func tableView(_ tableView: UITableView,
18                   willDisplay cell: UITableViewCell,
19                   forRowAt indexPath: IndexPath) {
20        heightCache[indexPath] = cell.frame.height
21    }
22
23    func tableView(_ tableView: UITableView,
24                   estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
25        return heightCache[indexPath] ?? 120
26    }
27
28    // MARK: - Data Updates
29
30    func refreshFeed(_ newItems: [FeedItem]) {
31        // Invalidate cache for changed items
32        for (index, item) in newItems.enumerated() {
33            if index < items.count && items[index].id != item.id {
34                heightCache.removeValue(forKey: IndexPath(row: index, section: 0))
35            }
36        }
37        items = newItems
38        tableView.reloadData()
39    }
40}