How do you keep long lists smooth?

A ListView constructs only the children near the viewport when it can estimate extent. ListView.builder does that by default. Fixed extents make scrolling and jump-to-index cheaper because the viewport does not need to measure every child. Large images should be decoded at display size rather than full resolution.

ListView.builder(
  itemCount: messages.length,
  itemExtent: 72,
  itemBuilder: (context, index) {
    final message = messages[index];
    return MessageTile(key: ValueKey(message.id), message: message);
  },
)

• Use itemExtent or prototypeItem when rows share a predictable height
• Avoid shrinkWrap inside another scrollable on long content
• Add pagination or infinite scrolling instead of loading thousands of rows at once
• Use const widgets and split large rows so rebuilds stay local
• Pass cacheWidth to Image.network for thumbnails
• Avoid work in itemBuilder such as sorting the whole list on every row

What to measure

Profile in profile mode and inspect frame timings while scrolling. Distinguish UI-thread time spent building rows from raster time spent drawing images or shadows. Rebuild counts help find a row that rebuilds on every frame. If images dominate, resize and cache them; if building dominates, simplify the row widget.