didAdoptChild method
Called during RenderSliverVariableSizeBoxAdaptor.adoptChild.
Subclasses must ensure that the SliverVariableSizeBoxAdaptorParentData.index field of the child's RenderObject.parentData accurately reflects the child's index in the child list after this function returns.
Implementation
@override
void didAdoptChild(RenderBox child) {
assert(_currentlyUpdatingChildIndex != null);
final childParentData =
child.parentData! as SliverVariableSizeBoxAdaptorParentData;
childParentData.index = _currentlyUpdatingChildIndex;
}