Firestore in Dartpad

main.dart

// https://twitter.com/creativemaybeno/status/1458523044557770755?s=20

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:flutter/material.dart';

Future<void> main() async {
  await Firebase.initializeApp(
    options: const FirebaseOptions(
      apiKey: 'AIzaSyCEfiLLknrsFhk6VCUdKKvOjrWEaJp61uQ',
      authDomain: 'dart-pad-counter.firebaseapp.com',
      projectId: 'dart-pad-counter',
      storageBucket: 'dart-pad-counter.appspot.com',
      messagingSenderId: '391018863530',
      appId: '1:391018863530:web:416db91d2502a0179ee9d3',
    ),
  );
  runApp(const CounterApp());
}

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Firestore Counter demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const Counter(),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const Text(
              'The world has pressed the button this many times:',
            ),
            StreamBuilder<DocumentSnapshot>(
                stream: FirebaseFirestore.instance
                    .doc('collection/doc')
                    .snapshots(),
                builder: (context, snapshot) {
                  return Text(
                    snapshot.data?.get('number')?.toString() ?? '?',
                    style: Theme.of(context).textTheme.headline4,
                  );
                }),
            Image.network('https://i.imgur.com/AoXaWBY.png'),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          FirebaseFirestore.instance
              .doc('collection/doc')
              .update({'number': FieldValue.increment(1)});
        },
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}