Flutter ListView.Builder() 动态列表 - 显示数据但有错误

Question

您好，我正在尝试向用户显示新（和旧）版本的应用程序以及更改列表。我创建了一些功能和弹出消息，他们可以在其中查看版本和更改列表。

它有效，但当它显示版本和更改时，它还会显示无限红色字段，并在新版本下出现错误：

RangeError (index): Index out of range: index should be less than 1: 1

旧版本也一样：

RangeError (index): Index out of range: index should be less than 6: 6

我认为 ListView.Builder() 或我发送给它的内容可能有问题。有人可以帮忙吗？

代码：

    Future<void> displayNewVersion() async {
    List _versions = await readJson(); //geting data from Json
    Map<String, bool> _control = await controlSeenVersions(_versions); //sorting what version changes was seen or not
    Map<String, List<dynamic>> _listSeen = {}, _listNotSeen = {};

    for (var version in _versions) {
      if (_control[version["vName"]]) {
        _listSeen[version["vName"]] = version["changes"];
      } else {
        _listNotSeen[version["vName"]] = version["changes"];
      }
    }

    if (_listNotSeen.isNotEmpty) {
      showChangelog(_listNotSeen, _listSeen, _versions);
    }
  }

显示新版本的功能

showChangelog(Map<String, List<dynamic>> _listNotSeen, Map<String, List<dynamic>> _listSeen, List _versions) async {
var shortestSide = MediaQuery.of(context).size.shortestSide;
final bool isPhone = shortestSide < 600;
customDialogWithHeaderSE(
    context,
    isPhone,
    LocaleKeys.newVersionTitle + _versions[0]["vName"],
    //StatefulBuilder must be here coz you need context and context of dialog itself coz one pop dialog and second navigate..
    Container(
      margin: const EdgeInsets.all(8.0),
      width: 300.0,
      child: Expanded(
        child: ListView.builder(
          scrollDirection: Axis.vertical,
          shrinkWrap: true,
          itemCount: _versions.length,
          itemBuilder: (context, int index) {
            String key = _listNotSeen.keys.elementAt(index);
            return Container(
                child: Column(
                  children: <Widget>[
                  new ListTile(
                    title: new Text(key.toString(),
                        style: TextStyle(fontWeight: FontWeight.bold)),
                    subtitle: Container(
                      child: ListView.builder(
                          physics: const NeverScrollableScrollPhysics(),
                          shrinkWrap: true,
                          itemCount: _listNotSeen[key].length,
                          itemBuilder: (context, int index) {
                            return Container(
                                child:
                                    Text("- " + _listNotSeen[key][index]));
                          }),
                    )),
                new Divider(
                  height: 2.0,
                ),
              ],
            ));
          },
        ),
      ),
    ),
    [
      if (_listSeen.isNotEmpty)
        Column(
          children: [
            ExpansionTile(
              title: Text(
                'Older releases',
                style: TextStyle(
                    fontWeight: FontWeight.w400,
                    color: ColorsApp.blue75_storaenso,
                    height: 1.5,
                    fontSize: (isPhone) ? 18.0 : 20.0),
              ),
              children: [
                // Change as per your requirement
                SizedBox(
                  height: 300.0, // Change as per your requirement
                  width: 300.0,
                  child: ListView.builder(
                      scrollDirection: Axis.vertical,
                      shrinkWrap: true,
                      itemCount: _versions.length,
                      itemBuilder: (context, int index) {
                        String key = _listSeen.keys.elementAt(index);
                        return Column(children: <Widget>[
                          new ListTile(
                            title: new Text(key.toString(), style: TextStyle(fontWeight: FontWeight.bold)),
                            subtitle: Container(
                              child: ListView.builder(
                                  physics: const NeverScrollableScrollPhysics(),
                                  shrinkWrap: true,
                                  itemCount: _listSeen[key].length,
                                  itemBuilder: (context, int index) {
                                    return Container(child: Text("- " + _listSeen[key][index]));
                                  }),
                            ),
                          ),
                          new Divider(
                            height: 2.0,
                          ),
                        ]);
                      }),
                ),
              ],
            ),
          ],
        ),

Answer 1

您似乎将 ListView.builder 小部件中的 itemCount: 设置为 _versions.length。 itemCount 是您的 builder: 函数运行的次数。如果itemCount是7那么builder:函数会运行7次，每次都会传入一个新的索引，即0,1,2,3,4,5,6 . 这不是问题，但是在您的 builder: 函数中您尝试索引 _listNotSeen 和 _listSeen。当这些元素少于 _versions 时，就会出现问题。例如，如果 _listNotSeen 有 4 个元素而 _versions 有 7 个元素，那么当索引达到 4 或更高时，您将超出范围。您需要将 _versions.length 替换为与 _listNotSeen 长度相等的内容或您在 builder: 函数中索引的任何内容

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