for https://stackoverflow.com/q/70665452/10976714

matrix_example_SO70665452.dart

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Flutter Demo Home Page'),
        ),
        body: const MyHomePage(),
      ),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: const <Widget>[
          MatrixOption(matrix: Matrix(1, 1)),
          MatrixOption(matrix: Matrix(2, 2)),
          MatrixOption(matrix: Matrix(3, 3)),
        ],
      ),
    );
  }
}

class Matrix {
  final int rows;
  final int columns;

  const Matrix(this.rows, this.columns);
}

class MatrixOption extends StatelessWidget {
  final Matrix matrix;
  const MatrixOption({
    Key? key,
    required this.matrix,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return InkWell(
      onTap: () {
        Navigator.of(context).push(
          MaterialPageRoute(
            builder: (context) {
              return Scaffold(
                appBar: AppBar(),
                body: MatrixPage(matrix: matrix),
              );
            },
          ),
        );
      },
      child: Container(
        height: 50,
        width: 100,
        margin: const EdgeInsets.all(8),
        color: Colors.orange,
        child: Center(child: Text('${matrix.rows}' 'x' '${matrix.columns} Matrix ')),
      ),
    );
  }
}

class MatrixPage extends StatefulWidget {
  final Matrix matrix;

  const MatrixPage({
    Key? key,
    required this.matrix,
  }) : super(key: key);

  @override
  State<MatrixPage> createState() => _MatrixPageState();
}

class _MatrixPageState extends State<MatrixPage> {
  // List of lists (outer list is the rows, inner list is the columns)
  final controllers = <List<TextEditingController>>[];
  late final rows = widget.matrix.rows;
  late final columns = widget.matrix.columns;

  @override
  void initState() {
    super.initState();
    createControllers();
  }

  void createControllers() {
    for (var i = 0; i < rows; i++) {
      controllers.add(List.generate(columns, (index) => TextEditingController(text: '0')));
    }
  }

  void printMatrix() {
    final strings = <List<String>>[];
    for (var controllerRow in controllers) {
      final row = controllerRow.map((e) => e.text).toList();
      strings.add(row);
    }
    print(strings);
  }

  @override
  void dispose() {
    for (var controllerRow in controllers) {
      for (final c in controllerRow) {
        c.dispose();
      }
    }
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        children: [
          Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: List.generate(
              controllers.length,
              (index1) => Row(
                mainAxisAlignment: MainAxisAlignment.center,
                children: List.generate(
                  controllers[index1].length,
                  (index2) => Center(
                    child: MatrixField(
                      controller: controllers[index1][index2],
                    ),
                  ),
                ),
              ),
            ),
          ),
          TextButton(
            onPressed: printMatrix,
            child: const Text('Print Matrix'),
          )
        ],
      ),
    );
  }
}

class MatrixField extends StatelessWidget {
  final TextEditingController controller;
  const MatrixField({
    Key? key,
    required this.controller,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SizedBox(
      height: 50,
      width: 50,
      child: TextField(
        controller: controller,
      ),
    );
  }
}