1. Create a Scaffold

                    return MaterialApp(
                      title: 'SnackBar Demo',
                      home: Scaffold(
                        appBar: AppBar(
                          title: const Text('SnackBar Demo'),
                        ),
                        body: const SnackBarPage(),
                      ),
                    );

                    

2. Display a SnackBar

                    const snackBar = SnackBar(
                      content: Text('Yay! A SnackBar!'),
                    );

                    // Find the ScaffoldMessenger in the widget tree
                    // and use it to show a SnackBar.
                    ScaffoldMessenger.of(context).showSnackBar(snackBar);

                    

3. Provide an optional action

                    final snackBar = SnackBar(
                        content: const Text('Yay! A SnackBar!'),
                        action: SnackBarAction(
                          label: 'Undo',
                          onPressed: () {
                            // Some code to undo the change.
                          },
                        ),
                      );

                      

Complete code

                      import 'package:flutter/material.dart';

                      void main() => runApp(const SnackBarDemo());

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

                        @override
                        Widget build(BuildContext context) {
                          return MaterialApp(
                            title: 'SnackBar Demo',
                            home: Scaffold(
                              appBar: AppBar(
                                title: const Text('SnackBar Demo'),
                              ),
                              body: const SnackBarPage(),
                            ),
                          );
                        }
                      }

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

                        @override
                        Widget build(BuildContext context) {
                          return Center(
                            child: ElevatedButton(
                              onPressed: () {
                                final snackBar = SnackBar(
                                  content: const Text('Yay! A SnackBar!'),
                                  action: SnackBarAction(
                                    label: 'Undo',
                                    onPressed: () {
                                      // Some code to undo the change.
                                    },
                                  ),
                                );

                                // Find the ScaffoldMessenger in the widget tree
                                // and use it to show a SnackBar.
                                ScaffoldMessenger.of(context).showSnackBar(snackBar);
                              },
                              child: const Text('Show SnackBar'),
                            ),
                          );
                        }
                      }