hello world

import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(
      title: 'HelloWorld',
      home: Scaffold(
        appBar: AppBar(
          title: const Text('HelloWorld'),
        ),
      ),
    ),
  );
}

This is pretty much the simplest meaningful flutter app. It displays a bar at the top of that app reading "HelloWorld". Often you want to split the app into two different subclasses of widget: a root-level FancyNameApp widget that never changes and a child MainScreen widget that rebuilds when messages are sent and internal state changes.

import 'package:flutter/material.dart';

void main() {
  runApp(
    const HelloApp(),
  );
}

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

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'HelloWorld',
      home: HelloScreen(),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('HelloWorld'),
      ),
    );
  }
}

Typically, in this example you would need to make HelloScreen stateful and create a state for it.