Optimizing UITableView Scrolling Performance: Cell Height Caching and Asynchronous Text Rendering

In recent years, user experience has become paramount for apps, and smooth scrolling lists are essential; noticeable lag can lead to negative feedback or uninstalls.

Two major optimizations are presented: avoiding repeated cell height calculations and asynchronous text rendering.

Avoid Recalculating Cell Height

Calling heightForRowAtIndexPath: frequently can cause jank. In iOS 8 you can enable automatic dimension with self.tableView.estimatedRowHeight = 88; and self.tableView.rowHeight = UITableViewAutomaticDimension; , but for performance‑critical screens it's better to cache heights. Libraries such as UITableView‑FDTemplateLayoutCell provide a cache, or you can compute frames manually after data fetch and store them.

Example code shows how to pre‑compute frames and cell height in a FrameModel and return the cached value in heightForRowAtIndexPath: .

self.tableView.estimatedRowHeight = 88;
self.tableView.rowHeight = UITableViewAutomaticDimension;

Asynchronous Text Rendering

Rendering large amounts of text on the main thread is CPU‑intensive. Using a custom text view based on TextKit or Core Text, or the ready‑made YYText library, allows text layout to be prepared off‑screen and drawn asynchronously, reducing duplicate calculations and memory usage.

By replacing boundingRectWithSize: and sizeWithAttributes: with YYText’s layout methods, a FrameYYModel stores a YYTextLayout that provides pre‑computed size and attributes. The cell then sets titleLabel.textLayout = model.titleLayout; and enables displaysAsynchronously .

// FrameYYModel.m
- (void)setEntity:(FDFeedEntity *)entity {
    // ...
    YYTextContainer *titleContainer = [YYTextContainer containerWithSize:CGSizeMake(maxLayout, CGFLOAT_MAX)];
    _titleLayout = [YYTextLayout layoutWithContainer:titleContainer text:title];
    // ...
}

Both approaches have trade‑offs: cached height libraries simplify implementation but still incur Auto Layout overhead; manual frame calculation eliminates that overhead but requires more code. YYText offers smooth scrolling but may cause flicker when cells are refreshed asynchronously.

Additional tips include limiting the number of views with rounded corners and using Instruments’ Time Profiler to pinpoint performance bottlenecks.

Conclusion

Combining UITableView‑FDTemplateLayoutCell (or manual frame caching) with YYText yields the best list performance; choose the solution that fits your project’s time constraints and visual requirements.