Dart code for a flutter hello world app

main.dart

import 'package:flutter/material.dart';

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

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

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  TextEditingController nameTextController = TextEditingController();
  String greeting = "Hello World!";
  void greetUser() {
    if (nameTextController.text != null) {
      String name = nameTextController.text;
      setState(() {
        greeting = "Hello $name";
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text(widget.title),
        ),
        body: Column(children: [
          SizedBox(
            height: 16.0,
          ),
          Text(greeting),
          TextField(
            controller: nameTextController,
          ),
          MaterialButton(
            onPressed: () => greetUser(),
            child: Text("Submit"),
          ),
        ]));
  }
}