dart - Flutter - 当我尝试在 ListView 生成器中创建扩展面板列表时，展开和折叠功能不起作用

Question

Flutter - 当我尝试在 ListView 生成器中创建扩展面板列表时，展开和折叠功能不起作用。当我在扩展调用中验证索引值时，它总是返回 0。因此它没有正确执行，但我不知道如何解决它。我提供了我的大代码库的片段。

class EventsPage extends StatefulWidget {
  @override
  _EventsPageState createState() {
    return _EventsPageState();
  }
}
class _EventsPageState extends State<EventsPage> {
  EventsApi _eventsApi = new EventsApi();
  Future<List<EventList>> fetchPost;
  List<bool> _isExpanded;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    fetchPost = _eventsApi.fetchPost('2017-06-01', '2018-12-10');
  }

  void expandList(int length) {
    _isExpanded = new List(length);
    _isExpanded.fillRange(0, length - 1, false);
  }

  @override
  Widget build(BuildContext context) {
    return Container(
        child: FutureBuilder<List<EventList>>(
      future: fetchPost,
      builder: (context, snapshot) {
        if (snapshot.hasData) {
          expandList(snapshot.data.length); //initialize the expand list
          return Container(
            child: ListView.builder(
                itemCount: snapshot.data.length,
                itemBuilder: (context, index) {
                    return ExpansionPanelList(
                      animationDuration: Duration(milliseconds: 500),
                      expansionCallback: (int index, bool isExpanded) {
                        setState(() {});
                      },
                      children: <ExpansionPanel>[
                        ExpansionPanel(
                          headerBuilder: (context, isExpanded) {
                            return Text(" my tile number was $index");
                          },
                          isExpanded: true,
                          body: Container(color: Colors.black),
                        )
                      ],
                    );
                }),
          );
        }

Answer 1

你的代码有一些错误，我修正了它，这里有一个示例:

  class _EventsPageState extends State<EventsPage> {
      List<String> fetchPost;
      List<bool> _isExpanded;

      Future<List<String>> loadData() async {
        await Future.delayed(Duration(seconds: 3));
        return List.generate(20, (index) => "$index").toList();
      }

      void expandList(int length) {
        if (_isExpanded == null) {
          _isExpanded = new List(length);
          _isExpanded.fillRange(0, length - 1, false);
        }
      }

      @override
      Widget build(BuildContext context) {
        return Scaffold(
          body: Container(
              child: FutureBuilder<List<String>>(
                  future: loadData(),
                  builder: (context, snapshot) {
                    if (snapshot.hasData) {
                      expandList(snapshot.data.length); //initialize the expand list
                      return SingleChildScrollView(
                        child: ExpansionPanelList(
                            animationDuration: Duration(milliseconds: 500),
                            expansionCallback: (int index, bool isExpanded) {
                              setState(() {
                                _isExpanded[index] = !isExpanded;
                                print("INDEX : $index ... $isExpanded");
                              });
                            },
                            children: buildPanelList(snapshot.data)),
                      );
                    } else {
                      return Center(
                        child: CircularProgressIndicator(),
                      );
                    }
                  })),
        );
      }

      List<ExpansionPanel> buildPanelList(List<String> data) {
        List<ExpansionPanel> children = List<ExpansionPanel>();
        for (int i = 0; i < data.length; i++) {
          children.add(ExpansionPanel(
            headerBuilder: (context, isExpanded) {
              return Text(" my tile number was $i");
            },
            isExpanded: _isExpanded[i] ?? false,
            body: Container(
              color: Colors.black,
            ),
          ));
        }
        return children;
      }
    }