Jumping to a particular sliver in a flutter sliverlist - flutter

Question

How can I programmatically jump (or scroll) to a particular sliver in a sliver list where the slivers vary in height? The code below loads the text of a book into a custom scroll view, with a chapter for each widget. When the action button is pressed I want the view to jump to chapter 3, but nothing happens. What am I doing wrong?
class BookPage extends StatefulWidget {
BookPage({Key? key, this.title = "book"}) : super(key: key);
String title;
final _chapter3key = new GlobalKey(debugLabel: "chap3key");
get chapter3Key => _chapter3key;
#override
_BookState createState() => _BookState();
}
class _BookState extends State<BookPage> {
ScrollController? scrollController = new ScrollController();
Map<int, String> chapterHTML = {};
String title = "";
final chapterCount=10;
void fetchText() async {
for (int i = 1; i <= 10; i++) {
chapterHTML[i] = await getChapterHtml(i);
}
setState(() {});
}
_BookState() {
fetchText();
}
Widget chapterSliver(int i) {
if (i==3) {
return Html(key: widget.chapter3Key, data: chapterHTML[i] ?? "", );
}
return Html(
data: chapterHTML[i] ?? "",
);
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: CustomScrollView(controller: scrollController, slivers: [
SliverList(
delegate: SliverChildBuilderDelegate ((BuildContext context, int index) {
if (index > chapterCount) return null;
return chapterSliver(index);
}// first sliver is empty (chapter 0!)
))
]),
floatingActionButton: FloatingActionButton(onPressed: () {
Scrollable.ensureVisible(widget.chapter3Key.currentContext);
})
);
}
}

Answer 1

For anyone finding this question, I've found a solution - use a
scrollablePositionedList