@@ -521,6 +521,113 @@ class SliverFixedExtentList extends SliverMultiBoxAdaptorWidget {
521521 }
522522}
523523
524+ /// A sliver that places its box children in a linear array and constrains them
525+ /// to have the corresponding extent returned by [itemExtentBuilder] .
526+ ///
527+ /// _To learn more about slivers, see [CustomScrollView.slivers] ._
528+ ///
529+ /// [SliverVariedExtentList] arranges its children in a line along
530+ /// the main axis starting at offset zero and without gaps. Each child is
531+ /// constrained to the corresponding extent along the main axis
532+ /// and the [SliverConstraints.crossAxisExtent] along the cross axis.
533+ ///
534+ /// [SliverVariedExtentList] is more efficient than [SliverList] because
535+ /// [SliverVariedExtentList] does not need to lay out its children to obtain
536+ /// their extent along the main axis. It's a little more flexible than
537+ /// [SliverFixedExtentList] because this allow the children to have different extents.
538+ ///
539+ /// See also:
540+ ///
541+ /// * [SliverFixedExtentList] , whose children are forced to a given pixel
542+ /// extent.
543+ /// * [SliverPrototypeExtentList] , which is similar to [SliverFixedExtentList]
544+ /// except that it uses a prototype list item instead of a pixel value to define
545+ /// the main axis extent of each item.
546+ /// * [SliverList] , which does not require its children to have the same
547+ /// extent in the main axis.
548+ /// * [SliverFillViewport] , which sizes its children based on the
549+ /// size of the viewport, regardless of what else is in the scroll view.
550+ class SliverVariedExtentList extends SliverMultiBoxAdaptorWidget {
551+ /// Creates a sliver that places box children with the same main axis extent
552+ /// in a linear array.
553+ const SliverVariedExtentList ({
554+ super .key,
555+ required super .delegate,
556+ required this .itemExtentBuilder,
557+ });
558+
559+ /// A sliver that places multiple box children in a linear array along the main
560+ /// axis.
561+ ///
562+ /// [SliverVariedExtentList] places its children in a linear array along the main
563+ /// axis starting at offset zero and without gaps. Each child is forced to have
564+ /// the returned extent of [itemExtentBuilder] in the main axis and the
565+ /// [SliverConstraints.crossAxisExtent] in the cross axis.
566+ ///
567+ /// This constructor is appropriate for sliver lists with a large (or
568+ /// infinite) number of children whose extent is already determined.
569+ ///
570+ /// Providing a non-null `itemCount` improves the ability of the [SliverGrid]
571+ /// to estimate the maximum scroll extent.
572+ SliverVariedExtentList .builder ({
573+ super .key,
574+ required NullableIndexedWidgetBuilder itemBuilder,
575+ required this .itemExtentBuilder,
576+ ChildIndexGetter ? findChildIndexCallback,
577+ int ? itemCount,
578+ bool addAutomaticKeepAlives = true ,
579+ bool addRepaintBoundaries = true ,
580+ bool addSemanticIndexes = true ,
581+ }) : super (delegate: SliverChildBuilderDelegate (
582+ itemBuilder,
583+ findChildIndexCallback: findChildIndexCallback,
584+ childCount: itemCount,
585+ addAutomaticKeepAlives: addAutomaticKeepAlives,
586+ addRepaintBoundaries: addRepaintBoundaries,
587+ addSemanticIndexes: addSemanticIndexes,
588+ ));
589+
590+ /// A sliver that places multiple box children in a linear array along the main
591+ /// axis.
592+ ///
593+ /// [SliverVariedExtentList] places its children in a linear array along the main
594+ /// axis starting at offset zero and without gaps. Each child is forced to have
595+ /// the returned extent of [itemExtentBuilder] in the main axis and the
596+ /// [SliverConstraints.crossAxisExtent] in the cross axis.
597+ ///
598+ /// This constructor uses a list of [Widget] s to build the sliver.
599+ SliverVariedExtentList .list ({
600+ super .key,
601+ required List <Widget > children,
602+ required this .itemExtentBuilder,
603+ bool addAutomaticKeepAlives = true ,
604+ bool addRepaintBoundaries = true ,
605+ bool addSemanticIndexes = true ,
606+ }) : super (delegate: SliverChildListDelegate (
607+ children,
608+ addAutomaticKeepAlives: addAutomaticKeepAlives,
609+ addRepaintBoundaries: addRepaintBoundaries,
610+ addSemanticIndexes: addSemanticIndexes,
611+ ));
612+
613+ /// The children extent builder.
614+ ///
615+ /// Should return null if asked to build an item extent with a greater index than
616+ /// exists.
617+ final ItemExtentBuilder itemExtentBuilder;
618+
619+ @override
620+ RenderSliverVariedExtentList createRenderObject (BuildContext context) {
621+ final SliverMultiBoxAdaptorElement element = context as SliverMultiBoxAdaptorElement ;
622+ return RenderSliverVariedExtentList (childManager: element, itemExtentBuilder: itemExtentBuilder);
623+ }
624+
625+ @override
626+ void updateRenderObject (BuildContext context, RenderSliverVariedExtentList renderObject) {
627+ renderObject.itemExtentBuilder = itemExtentBuilder;
628+ }
629+ }
630+
524631/// A sliver that places multiple box children in a two dimensional arrangement.
525632///
526633/// _To learn more about slivers, see [CustomScrollView.slivers] ._
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