How to prevent Flutter app from scrolling to top after calling setState?

Question

I have an ExpansionPanelList inside a SingleChildScrollView. Whenever I (un)fold a panel and therefore call setState, the SingleChildScrollView scrolls back to the top. How can I prevent this?

@override
Widget build(BuildContext context) {
  final _scaffoldKey = new GlobalKey<ScaffoldState>();
  return new Scaffold(
    key: _scaffoldKey,
    appBar: new AppBar(
      title: new Text(widget.title),
    ),
    body: new SingleChildScrollView(
      child: new ExpansionPanelList(
        children: <ExpansionPanel>[
          // panels
        ],
        expansionCallback: (int index, bool isExpanded) {
          setState(() {
            // toggle expanded
          });
        },
      ), // ExpansionPanelList
    ), // SingleChildScrollView
  ); // Scaffold
}

---

This answer suggests using a custom ScrollController with keepScrollOffset set to true, however this is the default value and setting it explicitly to true therefore does not change anything.

Answer 1

That's because you are using a new Key every time you rebuild the widget (setState).

To fix your issue just move the code below outside the build method

 final _scaffoldKey = new GlobalKey<ScaffoldState>(); 

Like this :

 final _scaffoldKey = new GlobalKey<ScaffoldState>();

    @override
    Widget build(BuildContext context) {
      return new Scaffold(
        key: _scaffoldKey,
        appBar: new AppBar(
          title: new Text(widget.title),
        ),