How do you optimize table views in iOS for performance?

Official answer

Start by reproducing a scrolling hitch or memory problem on a representative device and dataset. Use Instruments to distinguish main-thread work, layout/drawing cost, image decoding and retained memory before choosing an optimization.

• Reuse and configure cells consistently. Dequeue reusable cells and reset transient state. Configure each cell from its current model; do not depend on what a previous row left in it.
• Keep expensive work out of cell configuration. Fetch data asynchronously and prepare appropriately sized images. Bound caches and request concurrency, and update UIKit on the main thread. A cell reused for item B must not display a late result for item A: associate work with stable item identity, verify that identity before applying a result, and cancel or detach obsolete work.
• Reduce measured layout/rendering cost. Simplify unnecessary view hierarchies and constraints. Every UIView is already backed by a layer; using CALayer properties is not inherently an alternative that guarantees faster rendering. Shadows, masks and blending can have costs. Profile the actual case and preserve the intended appearance.
• Prefetch opportunistically. UITableViewDataSourcePrefetching can start work before a row appears, but it is not called for every row. Cell configuration must handle cached, in-progress and not-yet-requested data. Coordinate cancellation with any visible consumer that still needs a shared request.
• Verify the result. Compare hitches, main-thread time and memory during fast scrolling and direction changes, including slow loads and repeated reuse. Preserve self-sizing, Dynamic Type and accessibility behavior.

Do not claim a performance improvement from adding caching or moving a task off the main thread alone. Confirm the bottleneck and repeat the same workload after the change.

Sources

Apple: table-view prefetching; asynchronous image loading; UIView.