How to implement controller on a nested ListView.builder in Flutter?

I have an implementation such that I need to have controller values inside nested list views. But I am getting the same values for the sub-list view. My problem is that I need to access the primary index so that the controller values remain distinct for each list index. Here is the minimal code representation for the same.

import 'package:flutter/material.dart';

class NestedLists extends StatefulWidget {
  const NestedLists({super.key});

  @override
  State<NestedLists> createState() => _NestedListsState();
}

class _NestedListsState extends State<NestedLists> {
  List<Map<String, dynamic>> mainList = [];
  List<TextEditingController> xControllers = [];
  List<TextEditingController> yControllers = [];

  @override
  Widget build(BuildContext context) {
    return SafeArea(
      child: Scaffold(
        body: Padding(
          padding: const EdgeInsets.all(10.0),
          child: SingleChildScrollView(
            child: Column(
              children: [
                Row(
                  mainAxisAlignment: MainAxisAlignment.spaceBetween,
                  children: [
                    const Text('Add Nested Lists'),
                    ElevatedButton(
                      onPressed: () {
                        setState(() {
                          mainList.add({
                            'sub_list': [],
                          });
                        });
                      },
                      child: const Text('Add another List'),
                    ),
                  ],
                ),
                if (mainList.isNotEmpty)
                  ListView.builder(
                    shrinkWrap: true,
                    itemCount: mainList.length,
                    itemBuilder: (BuildContext context, int index) => Padding(
                      padding: const EdgeInsets.all(10.0),
                      child: Card(
                        child: Padding(
                          padding: const EdgeInsets.all(20.0),
                          child: Column(
                            children: [
                              Row(
                                mainAxisAlignment:
                                    MainAxisAlignment.spaceBetween,
                                children: [
                                  Text(
                                    'Index $index',
                                  ),
                                  ElevatedButton(
                                    onPressed: () {
                                      setState(() {
                                        mainList[index]['sub_list'].add({});
                                      });
                                    },
                                    child: const Text('Add Sub List'),
                                  ),
                                ],
                              ),
                              if (mainList[index]['sub_list'].isNotEmpty)
                                Padding(
                                  padding: const EdgeInsets.all(20.0),
                                  child: ListView.builder(
                                    shrinkWrap: true,
                                    itemCount:
                                        mainList[index]['sub_list'].length,
                                    itemBuilder:
                                        (BuildContext context, int sIndex) {
                                      xControllers.add(
                                        TextEditingController(text: ''),
                                      );
                                      yControllers.add(
                                        TextEditingController(text: ''),
                                      );
                                      return Row(
                                        children: [
                                          Expanded(
                                              child: TextFormField(
                                            controller: xControllers[sIndex],
                                            decoration: const InputDecoration(
                                              border: OutlineInputBorder(),
                                            ),
                                          )),
                                          const SizedBox(
                                            width: 50,
                                          ),
                                          Expanded(
                                            child: TextFormField(
                                              controller: yControllers[sIndex],
                                              decoration: const InputDecoration(
                                                border: OutlineInputBorder(),
                                              ),
                                            ),
                                          ),
                                        ],
                                      );
                                    },
                                  ),
                                ),
                            ],
                          ),
                        ),
                      ),
                    ),
                  )
              ],
            ),
          ),
        ),
      ),
    );
  }
}

Here is the screenshot of the issue.

YOu can clearly see that I am getting the same value for Index 0 and Index 1 as I type along. But in reality, it should be unique. Any help will be appreciated. Thanks.