https://medium.com/@datvt9312/bb6aba1586ac

my_app.dart

import 'package:flutter/material.dart';
import 'package:flutter_demo_setup/env.dart';

class MyApp extends StatelessWidget {
  final Env env;

  const MyApp({Key key, @required this.env}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(env: env),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.env}) : super(key: key);
  final Env env;
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Welcome'),
      ),
      body: Center(
        child: Text(
          'You are reading ${widget.env.secret}',
        ),
      ),
    );
  }
}