Flutter - RangeError（索引）：无效值：有效值范围为空：0

Posted 2023-02-23

【中文标题】Flutter - RangeError（索引）：无效值：有效值范围为空：0

【英文标题】：Flutter - RangeError (index): Invalid value: Valid value range is empty: 0

【发布时间】：2021-11-13 01:31:30

【问题描述】：

我想构建一个如下图所示的测验应用程序

但我得到了那个错误，那是因为组值的索引。 我是颤振和编码的新手，所以请帮助我。 我不知道如何解决它。

class _ReadingPage2State extends State<ReadingPage2> 
  bool _isloading = false;
  List<int> groupValue = [];
  List<List<int>> value = [];
  int questionId;

  Future<Response> loadQuestion() async 
    final url = Network().link('/exercise/1/questions');
    SharedPreferences localStorage = await SharedPreferences.getInstance();
    final token = jsonDecode(localStorage.getString('token'));
    http.Response response = await http.get(Uri.parse(url), headers: 
      'Content-Type': 'application/json',
      'Accept': 'application/json',
      'Authorization': 'Bearer $token',
    );
    if (response.statusCode == 200) 
      var jsonResponce = response.body;
      Response res = Response.fromJson(json.decode(jsonResponce));
      return res;
     else
      throw Exception('Failed to load Question');
  

  @override
  Widget build(BuildContext context) 
    return Scaffold(
      backgroundColor: Colors.white,
      appBar: AppBar(
        title: Text("Set 1"),
        backgroundColor: Colors.orange,
      ),
      body: SafeArea(
        child: Column(
          children: [
            Expanded(
              child: FutureBuilder<Response>(
                future: loadQuestion(),
                builder: (context, AsyncSnapshot<Response> snapshot) 
                  if (snapshot.hasData) 
                    List<Result> list = snapshot.data.result;
                    return ListView.builder(
                      itemCount: list.length + 1,
                      itemBuilder: (context, index) => index < list.length
                          ?
                          Column(
                              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                              mainAxisSize: MainAxisSize.max,
                              children: [
                                Container(
                                  child: Column(
                                    children: <Widget>[
                                      Text(
                                        snapshot
                                            .data.result[index].questionText,
                                        textAlign: TextAlign.center,
                                        style: TextStyle(
                                            fontSize: 20.0,
                                            fontWeight: FontWeight.w600),
                                      ),
                                      Container(
                                        width: 150,
                                        child: Row(
                                          children: <Widget>[
                                            Radio(
                                                value: snapshot
                                                    .data
                                                    .result[index]
                                                    .options[0]
                                                    .id,
                                                groupValue: groupValue[index],
                                                onChanged: (value) 
                                                  setState(() 
                                                    groupValue[index] = value;
                                                    print(groupValue[index]);
                                                  );
                                                ),
                                            Text(
                                                snapshot.data.result[index]
                                                    .options[0].option,
                                                style: TextStyle(fontSize: 20)),
                                          ],
                                        ),
                                      ),
                                      Container(
                                        width: 150,
                                        child: Row(
                                          children: <Widget>[
                                            Radio(
                                                value: snapshot
                                                    .data
                                                    .result[index]
                                                    .options[1]
                                                    .id,
                                                groupValue: groupValue[index],
                                                onChanged: (value) 
                                                  setState(() 
                                                    groupValue[index] = value;
                                                    print(groupValue[index]);
                                                  );
                                                ),
                                            Text(
                                                snapshot.data.result[index]
                                                    .options[1].option,
                                                style: TextStyle(fontSize: 20)),
                                          ],
                                        ),
                                      ),
                                      SizedBox(height: 25),
                                    ],
                                  ),
                                ),
                              ],
                            )
                          : MaterialButton(
                              minWidth: double.infinity,
                              height: 40,
                              onPressed: () 
                                saveAnswer(questionId, groupValue[index]);
                              ,
                              color: Color(0xFFFF9D00),
                              shape: RoundedRectangleBorder(
                                borderRadius: BorderRadius.circular(50),
                              ),
                              child: Text('Submit'),
                            ),
                    );
                   else if (snapshot.hasError) 
                    debugPrint("$snapshot.error");
                    return Text("$snapshot.error",
                        style: TextStyle(fontSize: 15));
                  
                  return Center(child: CircularProgressIndicator());
                ,
              ),
            ),
          ],
        ),
      ),
    );
  

如果我将默认值设置为组值，就可以了，并且可以显示问题。但我不想为其设置默认值。

【参考方案1】：

您正在从一个列表进行迭代，而列表确实从 0 开始索引，

所以，改变

 itemCount: list.length + 1,

到

 itemCount: list.length,

【讨论】：

实际上我放了+1，因为我在页面末尾做了材料按钮。我尝试删除它，但仍然遇到同样的错误