indexOf method
Returns the index of the given child, as given by the SliverMultiBoxAdaptorParentData.index field of the child's parentData.
Implementation
int indexOf(RenderBox child) {
assert(child != null);
final SliverMultiBoxAdaptorParentData childParentData = child.parentData;
assert(childParentData.index != null);
return childParentData.index;
}