Flutter - Expandable - How to keep the panel expanded when changing the state

Question

I am using the expandable package (https://pub.dev/packages/expandable), and when I call the setState () method when taping on a checkbox the expandable panel closes during the widget tree reconstruction.

When I call setState () I tell the controller to keep the panel expanded expController.expanded = true, but that doesn't work.

I researched and it seems to me that the solution would be to use a key, but my tests did not work.

Can someone help me? I need to change the state of the checkbox, but keep the panel expanded. Here is an sample from my code:

class ExpandableCard extends StatefulWidget {
  ExpandableCard({Key key}) : super(key: key);

  @override
  _ExpandableCardState createState() => _ExpandableCardState();
}

class _ExpandableCardState extends State<ExpandableCard> {
  var _value = false;

  @override
  Widget build(BuildContext context) {
    ExpandableController expController =
        new ExpandableController(initialExpanded: false);

    return ExpandableNotifier(
        controller: expController,
        child: Padding(
          padding: const EdgeInsets.all(2),
          child: Card(
            clipBehavior: Clip.antiAlias,
            child: Column(
              children: <Widget>[
                ScrollOnExpand(
                  scrollOnExpand: true,
                  scrollOnCollapse: false,
                  child: ExpandablePanel(
                    theme: const ExpandableThemeData(
                      headerAlignment: ExpandablePanelHeaderAlignment.center,
                      tapBodyToCollapse: false,
                      tapHeaderToExpand: true,
                      tapBodyToExpand: true,
                      hasIcon: true,
                    ),
                    header: Padding(
                      padding: EdgeInsets.all(10),
                      child: Text('HEADER'),
                    ),
                    collapsed: Padding(
                      padding: EdgeInsets.only(left: 4),
                      child: Column(
                        crossAxisAlignment: CrossAxisAlignment.start,
                        children: [
                          Text('collapsed'),
                        ],
                      ),
                    ),
                    expanded: Column(
                      crossAxisAlignment: CrossAxisAlignment.start,
                      children: <Widget>[
                        for (var _ in Iterable.generate(3))
                          Padding(
                            padding: EdgeInsets.only(left: 2, bottom: 2),
                            child: Row(
                              children: [
                                Checkbox(
                                  value: _value,
                                  onChanged: (bool value) {
                                    setState(() {
                                      this._value = value;
                                      expController.expanded = true;
                                    });
                                  },
                                ),
                                Text('Checkbox'),
                              ],
                            ),
                          ),
                      ],
                    ),
                    builder: (_, collapsed, expanded) {
                      return Padding(
                        padding:
                            EdgeInsets.only(left: 10, right: 10, bottom: 10),
                        child: Expandable(
                          collapsed: collapsed,
                          expanded: expanded,
                          theme: const ExpandableThemeData(crossFadePoint: 0),
                        ),
                      );
                    },
                  ),
                ),
              ],
            ),
          ),
        ));
  }
}

question from:https://stackoverflow.com/questions/65907296/flutter-expandable-how-to-keep-the-panel-expanded-when-changing-the-state

Answer 1

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