How do you ensure UI responsiveness and smooth scrolling in complex UITableViews?

Official answer

Profile a reproducible scroll trace on representative devices, data sizes and text settings. Distinguish main-thread work, image decoding, layout, database fetches and rendering before optimizing. Use frame/hitch and memory evidence rather than assuming a particular hierarchy is always slow.

Dequeue reusable cells and fully configure their visible state for the current model. Clear stale images/loading/error state as appropriate. Associate asynchronous work with a stable item identifier or request generation; when a response arrives, verify that the cell still represents that item. An index path can change after insertion or reordering, and a reused cell must not display the previous item's image.

Fetch asynchronously, downsample images to an appropriate pixel size and bound memory/cache usage. Account for display scale and invalidate cached variants when their inputs change. Cancel work that is no longer needed when safe, while avoiding cancellation of a shared request still needed by another row. Return UI changes to the main actor.

Prefetching can reduce waits, but UIKit need not prefetch every cell. Cell configuration must handle ready, in-flight and not-yet-requested data. Limit speculative work so rapid scrolling does not create an unbounded queue or download everything.

Use reasonable self-sizing constraints and estimates. If caching heights, include width, content, Dynamic Type and other layout-relevant inputs; invalidate when they change. Test reuse, rapid reverse scrolling, slow/error responses, rotation, larger text and right-to-left content. Reuse improves opportunities for efficiency but does not promise a fixed number of live cells or universally smooth scrolling.

Table prefetch contract, Performance measurement