Flutter: for loop or if-statement is not working perfectly

Question

I want a create a live exam app. Here is some question in a list and some answer under those question. Users can select only one answer from per question. That why I write a for loop , for check box select. Answer is select perfectly, but else option of if()else condition is not working perfectly. Where is my problem ? Please someone help me.

Here is my Code-

import 'package:flutter/material.dart';

class AnswerSheet extends StatefulWidget {
  @override
  _AnswerSheetState createState() => _AnswerSheetState();
}

class _AnswerSheetState extends State<AnswerSheet> {
  List answerSheet = [
    {
      "qNo": 1,
      "question": "Who are you ?",
      "answer": [
        {"ans": "Teacher", "isSelect": false},
        {"ans": "Student", "isSelect": false},
        {"ans": "Farmer", "isSelect": false},
        {"ans": "Developer", "isSelect": false},
      ]
    },
    {
      "qNo": 2,
      "question": "Where are you from ?",
      "answer": [
        {"ans": "India", "isSelect": false},
        {"ans": "Bangladesh", "isSelect": false},
        {"ans": "India", "isSelect": false},
        {"ans": "China", "isSelect": false},
      ]
    },
    {
      "qNo": 3,
      "question": "Where you born ?",
      "answer": [
        {"ans": "Dhaka", "isSelect": false},
        {"ans": "Barguna", "isSelect": false},
        {"ans": "Patuakhali", "isSelect": false},
        {"ans": "Gazipur", "isSelect": false},
      ]
    },
  ];

  @override
  Widget build(BuildContext context) {
    double _width = MediaQuery.of(context).size.width;
    double _height = MediaQuery.of(context).size.height;
    return Scaffold(
      body: Container(
        height: _height,
        width: _width,
        child: SingleChildScrollView(
          child: Column(
            children: answerSheet.map((questionList) {
              return Padding(
                padding: const EdgeInsets.all(20.0),
                child: Column(
                  children: [
                    Row(
                      children: [
                        Text(questionList["qNo"].toString()),
                        SizedBox(
                          width: 5,
                        ),
                        Text(
                          questionList["question"],
                          style: TextStyle(fontSize: 28),
                        ),
                      ],
                    ),
                    ListView.builder(
                        shrinkWrap: true,
                        physics: NeverScrollableScrollPhysics(),
                        itemCount: questionList["answer"].length,
                        itemBuilder: (buildContext, index) {
                          var answerIndex = questionList["answer"][index];
                          return Row(
                            children: [
                              Checkbox(
                                  value: answerIndex["isSelect"],
                                  onChanged: (value) {
                                    print(
                                        "Length is ${questionList["answer"].length}");
                                    for (var i = 0;
                                        i < questionList["answer"].length;
                                        i++) {
                                      print(
                                          "$i = ${questionList["answer"].indexOf(answerIndex)}");
                                      if (i ==
                                          questionList["answer"].indexOf(
                                              questionList["answer"][index])) {
                                        setState(() {
                                          answerIndex["isSelect"] = value;
                                        });
                                      } else {
                                        setState(() {
                                          questionList["answer"][i]
                                              ["is_selected"] = false;
                                        });
                                      }
                                    }

                                    print(answerIndex["isSelect"]);
                                  }),
                              Container(
                                color: answerIndex["isSelect"] == true
                                    ? Colors.green
                                    : null,
                                child: Text(
                                  answerIndex["ans"] ?? "",
                                  style: TextStyle(fontSize: 24),
                                ),
                              )
                            ],
                          );
                        })
                  ],
                ),
              );
            }).toList(),
          ),
        ),
      ),
    );
  }
}

Solution

Change the key of questionList["answer"][i]['is_select'] with isSelect

                                   else {
                                        setState(() {
                                          questionList["answer"][i]
                                              ["is_selected"] = false;
                                        });
                                      }