将存储在Firebase中的值相加，并在FutureBuilder中显示总数

import 'package:firebase_core/firebase_core.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

import 'package:cloud_firestore/cloud_firestore.dart';

final FirebaseFirestore firestore = FirebaseFirestore.instance;

import 'package:flutter/material.dart';

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return FutureBuilder<QuerySnapshot>(
      future: firestore.collection('values').get(),
      builder: (context, snapshot) {
        if (snapshot.connectionState == ConnectionState.waiting) {
          return CircularProgressIndicator();
        }
        if (snapshot.hasError) {
          return Text('Error: ${snapshot.error}');
        }
        int total = 0;
        snapshot.data.docs.forEach((doc) {
          total += doc.data()['value'];
        });
        return Text('Total: $total');
      },
    );
  }
}