SliverFixedExtentList

SliverFixedExtentList is a widget in the Flutter framework used for creating scrollable lists where each item has a fixed and predetermined size. It is part of the sliver system, which allows for more complex and custom scrolling effects within a scroll view. Unlike a regular ListView, SliverFixedExtentList is designed to be placed within a CustomScrollView.

The primary advantage of SliverFixedExtentList is its performance, especially when dealing with a large number of items. By knowing the exact size of each item beforehand, it can efficiently calculate which items are visible and only build those. This avoids the overhead of measuring each item individually during scrolling, which is necessary for widgets like SliverList when item sizes vary.

When using SliverFixedExtentList, you must provide the `itemExtent` property, which defines the fixed size of every child widget in pixels. You also provide a delegate, typically `SliverChildBuilderDelegate`, which is responsible for building the child widgets on demand as they scroll into view. This delegate takes a builder function that receives an index and returns the widget for that position.

SliverFixedExtentList is ideal for scenarios such as fixed-size grid layouts or lists where all elements share the same height or width, ensuring smooth and efficient scrolling performance.