Sending Flutter form data into an SQLite database

Question

I am a new Flutter developer trying to figure out how to send my form data into SQLite as an instance of a simple class I set up.

I am trying to create a new user in my SQLite database, by capturing the values from each form field, saving them and then sending a new User class instance to the database with those values.

Below is my dart.main file.

import 'package:flutter/material.dart';
import 'package:sqflite/sqflite.dart';
import 'dart:async';
import 'package:path/path.dart';
import 'database_helper.dart';
import 'user.dart';

void main() async {
  runApp(MyApp());
  var databasesPath = await getDatabasesPath();
  String path = join(databasesPath, 'v1.db');

  Database database = await openDatabase(path, version: 1,
      onCreate: (Database db, int version) async {
        // When creating the db, create the table
        await db.execute(
            'CREATE TABLE users (id INTEGER PRIMARY KEY, firstName TEXT, lastName TEXT, userName TEXT, password TEXT, score INTEGER, email TEXT)');
      });
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        theme: ThemeData(
          fontFamily: 'Roboto',
        ),
        home: Scaffold(
            appBar: AppBar(
              title: const Text("Sleppytime"),
            ),
            body: Center(
                child: Padding(
                    padding: EdgeInsets.all(20.0),
                    child: ListView(
                        children: [
                      Container(
                          width: 300,
                          child: Center(
                              child: Align(
                                  alignment: Alignment.center,
                                  child: Text(
                                    "Do you have trouble sleeping no matter what you do?",
                                    style:
                                        Theme.of(context).textTheme.headline4,
                                  )))),
                      Container(
                          width: 300,
                          child: Center(
                              child: Align(
                                  alignment: Alignment.center,
                                  child: MyCustomForm()
                              ))
                      )
                    ])))));
  }
}

class MyCustomForm extends StatefulWidget {
  @override
  MyCustomFormState createState() {
    return MyCustomFormState();
  }
}

// Define a corresponding State class.
// This class holds data related to the form.
class MyCustomFormState extends State<MyCustomForm> {
  // Create a global key that uniquely identifies the
  // Form widget and allows validation of the form.
  //
  // Note: This is a `GlobalKey<FormState>`,
  //       not a GlobalKey<MyCustomFormState>.
  final _formKey = GlobalKey<FormState>();

  // For listening to FormField changes, like onChanged
  final userNameListener = TextEditingController();
  final firstNameListener = TextEditingController();
  final lastNameListener = TextEditingController();
  final passwordListener = TextEditingController();

  @override
  void initState() {
    super.initState();
    // Start listening to changes.
    firstNameListener.addListener(_storeFormField);
    lastNameListener.addListener(_storeFormField);
    userNameListener.addListener(_storeFormField);
    passwordListener.addListener(_storeFormField);
  }

  @override
  void dispose() {
    // Clean up the controller when the widget is disposed.
    firstNameListener.dispose();
    lastNameListener.dispose();
    userNameListener.dispose();
    passwordListener.dispose();
    super.dispose();
  }

  _storeFormField() {
  }

  void _saveForm() {
    if(_formKey.currentState!.validate()) {
      _formKey.currentState!.save();
    }
  }


  @override
  Widget build(BuildContext context) {
    // Build a Form widget using the _formKey created above.
    return Form(
      key: _formKey,
      child: Column(
        children: <Widget>[
          TextFormField(
            // The validator receives the text that the user has entered.
              validator: (value) {
                if (value == null || value.isEmpty) {
                  return 'Please enter your first name';
                }
                return null;
              },
              onSaved: (value) => new User().firstName = value,
              controller: firstNameListener,
              autofocus: true,
              decoration: InputDecoration(
                hintText: 'First name',
              )
          ),
          TextFormField(
            // The validator receives the text that the user has entered.
            validator: (value) {
              if (value == null || value.isEmpty) {
                return 'Please enter your last name';
              }
              return null;
            },
            onSaved: (value) => new User().lastName = value,
            controller: lastNameListener,
            decoration: InputDecoration(
              hintText: 'Last name',
            ),
          ),
          TextFormField(
            // The validator receives the text that the user has entered.
            validator: (value) {
              if (value == null || value.isEmpty) {
                return 'Please enter a username';
              }
              return null;
            },
            onSaved: (value) => new User().userName = value,
            controller: userNameListener,
            decoration: InputDecoration(
              hintText: 'Username',
            ),
          ),
          TextFormField(
            // The validator receives the text that the user has entered.
            validator: (value) {
              if (value == null || value.isEmpty) {
                return 'Please enter a password';
              }
              return null;
            },
            onSaved: (value) => new User().password = value,
            controller: passwordListener,
            decoration: InputDecoration(
              hintText: 'Password',
            ),
            obscureText: true,
          ),
          ElevatedButton(
            onPressed: () {
              _saveForm();
              User.insertUser(User());
            },
            child: Text('Submit'),
          ),
        ],
      ),

    );
  }
}

And my User class:

import 'package:flutter/material.dart';
import 'package:sqflite/sqflite.dart';
import 'dart:async';
import 'package:path/path.dart';
export 'user.dart';

class User {
  final int? id;
  String? firstName;
  String? lastName;
  String? userName;
  String? password;
  int? score;
  final String? email;

  User({
    this.id,
    this.firstName,
    this.lastName,
    this.userName,
    this.password,
    this.score,
    this.email,
  });

  Map<String, dynamic> toMap() {
    return {
      'id': id,
      'firstName': firstName,
      'lastName': lastName,
      'userName': userName,
      'password': password,
      'score': score,
      'email': email
    };
  }

  @override
  String toString() {
    return 'User{id: $id, firstName: $firstName, lastName: $lastName, userName: $userName, password: $password, score: $score, email: $email}';
  }

  static Future<void> insertUser(User user) async {
    final db = await openDatabase('v1.db');
    await db.insert(
      'users',
      user.toMap(),
      conflictAlgorithm: ConflictAlgorithm.replace,
    );
  }
}

It looks like data is being passed to my database, but all the fields are 'null', so I'm not sending the values properly.