I am using ExpansionPanel in flutter(v3.0.4) like this(this is the minimal reproduce example):

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  Widget buildNewTasks(BuildContext context) {
    return ListView.builder(
      scrollDirection: Axis.vertical,
      shrinkWrap: true,
      itemCount: 2,
      itemBuilder: (BuildContext context, int index) {
        return Text(index.toString());
      },
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Column(
      children: [
        ExpansionPanelList(
          children: [
            ExpansionPanel(
                headerBuilder: (context, isExpanded) {
                  return ListTile(
                    title: Text("Todo"),
                  );
                },
                body: buildNewTasks(context),
                isExpanded: true,
                canTapOnHeader: true),
          ],
        )
      ],
    ));
  }
}

when I click the ExpansionPanel header, the child did not expand or collapse. Am I missing something? what should I do to make the ExpansionPanel expand and collapse when click the header?

CodePudding user response：

Yes, you have missed the expansionCallback which calls when the collapse/expand happens and isExpanded property value should be dynamic. it will need to change while collapsing or expanding.

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  Widget buildNewTasks(BuildContext context) {
    return ListView.builder(
      scrollDirection: Axis.vertical,
      shrinkWrap: true,
      itemCount: 2,
      itemBuilder: (BuildContext context, int index) {
        return Text(index.toString());
      },
    );
  }

  bool active = false;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Column(
      children: [
        ExpansionPanelList(
          expansionCallback: (panelIndex, expanded) {
            active = !active;
            setState(() {});
          },
          children: [
            ExpansionPanel(
                headerBuilder: (context, isExpanded) {
                  return ListTile(
                    title: Text("Todo"),
                  );
                },
                body: buildNewTasks(context),
                isExpanded: active,
                canTapOnHeader: true),
          ],
        )
      ],
    ));
  }
}