How To Populate Dropdownbutton Using Sqlite Database In Flutter

dependencies:
  flutter:
    sdk: flutter
  path: ^1.7.0
  path_provider: ^1.6.24
  sqflite: ^1.3.2+1
  http: ^0.12.2

flutter pub get

import 'package:flutter/material.dart';
import 'dart:async';
import 'dart:io' as io;
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';
import 'package:path_provider/path_provider.dart';
import 'package:http/http.dart' as http;

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: MyHomePage(),
    );
  }
}
class MyHomePage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => MyHomePageState();
}

class MyHomePageState extends State<MyHomePage> {
  DatabaseHelper db = DatabaseHelper();

  //Add data to db
  _saveData() async {
    UserModel user1 = UserModel(
      "Jone",
      "Jone Jonathan",
      "Jone@gmail.com",
      "Jonpass",
    );

    UserModel user2 = UserModel(
      "Jony",
      "BajarangiSoft.com",
      "info@BajarangiSoft.com",
      "Jony",
    );
    await db.saveData(user1);
    await db.saveData(user2);
  }

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

  UserModel _currentUser;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.indigo,
        title: Text('Fetching Data From Sqlite Db - Dropdownbutton'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          mainAxisSize: MainAxisSize.max,
          children: <Widget>[
            FutureBuilder<List<UserModel>>(
                future: db.getUserModelData(),
                builder: (BuildContext context,
                    AsyncSnapshot<List<UserModel>> snapshot) {
                  if (!snapshot.hasData) return CircularProgressIndicator();
                  return DropdownButton<UserModel>(
                    items: snapshot.data
                        .map((user) => DropdownMenuItem<UserModel>(
                      child: Text(user.name),
                      value: user,
                    ))
                        .toList(),
                    onChanged: (UserModel value) {
                      setState(() {
                        _currentUser = value;
                      });
                    },
                    isExpanded: false,
                    //value: _currentUser,
                    hint: Text('Select User'),
                  );
                }),
            SizedBox(height: 20.0),
            _currentUser != null
                ? Text(
              "Name: " +
                  _currentUser.name +
                  "\n Email: " +
                  _currentUser.email +
                  "\n Username: " +
                  _currentUser.username +
                  "\n Password: " +
                  _currentUser.password,
            )
                : Text("No User selected"),
          ],
        ),
      ),
    );
  }
}


class UserModel {
  String username;
  String name;
  String email;
  String password;

  UserModel(
      this.username,
      this.name,
      this.email,
      this.password,
      );

  UserModel.fromMap(dynamic obj) {
    this.name = obj["name"];
    this.username = obj["username"];
    this.email = obj["email"];
    this.password = obj["password"];
  }

  Map<String, dynamic> toMap() {
    var map = new Map<String, dynamic>();

    map["username"] = username;
    map["name"] = name;
    map["email"] = email;
    map["password"] = password;

    return map;
  }

  //Getters
  String get getName => name;
  String get getUsername => username;
  String get getPassword => password;
  String get getEmail => email;
}

class DatabaseHelper {
  static final DatabaseHelper _instance = new DatabaseHelper.internal();
  factory DatabaseHelper() => _instance;

  static Database _db;

  Future<Database> get db async {
    if (_db != null) return _db;
    _db = await initDb();
    return _db;
  }

  DatabaseHelper.internal();

  initDb() async {
    io.Directory documentsDirectory = await getApplicationDocumentsDirectory();
    String path = join(documentsDirectory.path, "main.db");
    var theDb = await openDatabase(path, version: 1, onCreate: _onCreate);
    return theDb;
  }

  void _onCreate(Database db, int version) async {
    await db.execute("""CREATE TABLE user(
        id INTEGER PRIMARY KEY,
        username TEXT,
        email TEXT,
        name TEXT,
        password TEXT
        )""");
  }

  Future<int> saveData(UserModel user) async {
    var dbClient = await db;
    int res = await dbClient.insert("user", user.toMap());
    return res;
  }

  Future<List<UserModel>> getUserModelData() async {
    var dbClient = await db;
    String sql;
    sql = "SELECT * FROM user";

    var result = await dbClient.rawQuery(sql);
    if (result.length == 0) return null;

    List<UserModel> list = result.map((item) {
      return UserModel.fromMap(item);
    }).toList();

    print(result);
    return list;
  }
}