Dart 2.14 & Flutter 2.5 : ScaffoldMessenger SnackBar & Banner

main.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) => MaterialApp(
    home: MyHomePage(),
  );
}

class MyHomePage extends StatelessWidget{
  @override
  Widget build(BuildContext context) => Scaffold(
    appBar: AppBar(
      title: const Text('Material Banner & SnackBar'),
    ),
    body: Container(
      width: MediaQuery.of(context).size.width,
      child: Column(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        children: [
          
          ElevatedButton(
            child: const Text('Show MaterialBanner'),
            onPressed: () => ScaffoldMessenger.of(context).showMaterialBanner(
              MaterialBanner(
                content: const Text('Hello, I am a Material Banner'),
                leading: const Icon(Icons.info),
                backgroundColor: Colors.yellow,
                actions: [
                  TextButton(
                    child: const Text('Dismiss'),
                    onPressed: () => ScaffoldMessenger.of(context)
                    .hideCurrentMaterialBanner(),
                  ),
                ],
              ),
            ),
          ),

          ElevatedButton(
            child: const Text('Show SnackBar'),
            onPressed: () => ScaffoldMessenger.of(context).showSnackBar(
              const SnackBar(
                content: Text('Content')
              )
            ),
          )
          
        ]
      ),
    )
  );

}