SliverFixedExtentList.builder constructor

SliverFixedExtentList.builder({
  1. Key? key,
  2. required NullableIndexedWidgetBuilder itemBuilder,
  3. required double itemExtent,
  4. ChildIndexGetter? findChildIndexCallback,
  5. int? itemCount,
  6. bool addAutomaticKeepAlives = true,
  7. bool addRepaintBoundaries = true,
  8. bool addSemanticIndexes = true,
})

A sliver that places multiple box children in a linear array along the main axis.

SliverFixedExtentList places its children in a linear array along the main axis starting at offset zero and without gaps. Each child is forced to have the itemExtent in the main axis and the SliverConstraints.crossAxisExtent in the cross axis.

This constructor is appropriate for sliver lists with a large (or infinite) number of children whose extent is already determined.

Providing a non-null itemCount improves the ability of the SliverGrid to estimate the maximum scroll extent.

itemBuilder will be called only with indices greater than or equal to zero and less than itemCount.

It is legal for itemBuilder to return null. If it does, the scroll view will stop calling itemBuilder, even if it has yet to reach itemCount. By returning null, the ScrollPosition.maxScrollExtent will not be accurate unless the user has reached the end of the ScrollView. This can also cause the Scrollbar to grow as the user scrolls.

For more accurate ScrollMetrics, consider specifying itemCount.

The itemExtent argument is the extent of each item.

The findChildIndexCallback corresponds to the SliverChildBuilderDelegate.findChildIndexCallback property. If null, a child widget may not map to its existing RenderObject when the order of children returned from the children builder changes. This may result in state-loss. This callback needs to be implemented if the order of the children may change at a later time.

The addAutomaticKeepAlives argument corresponds to the SliverChildBuilderDelegate.addAutomaticKeepAlives property. The addRepaintBoundaries argument corresponds to the SliverChildBuilderDelegate.addRepaintBoundaries property. The addSemanticIndexes argument corresponds to the SliverChildBuilderDelegate.addSemanticIndexes property.

This example, which would be inserted into a CustomScrollView.slivers list, shows an infinite number of items in varying shades of blue:
link 
SliverFixedExtentList.builder(
  itemExtent: 50.0,
  itemBuilder: (BuildContext context, int index) {
    return Container(
      alignment: Alignment.center,
      color: Colors.lightBlue[100 * (index % 9)],
      child: Text('list item $index'),
    );
  },
)

Implementation

SliverFixedExtentList.builder({
  super.key,
  required NullableIndexedWidgetBuilder itemBuilder,
  required this.itemExtent,
  ChildIndexGetter? findChildIndexCallback,
  int? itemCount,
  bool addAutomaticKeepAlives = true,
  bool addRepaintBoundaries = true,
  bool addSemanticIndexes = true,
}) : super(delegate: SliverChildBuilderDelegate(
       itemBuilder,
       findChildIndexCallback: findChildIndexCallback,
       childCount: itemCount,
       addAutomaticKeepAlives: addAutomaticKeepAlives,
       addRepaintBoundaries: addRepaintBoundaries,
       addSemanticIndexes: addSemanticIndexes,
     ));