问ListView在颤振中找不到方向性Widget

EN

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

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

class MyApp extends StatelessWidget {
  final db = FirebaseFirestore.instance;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(  // Column, Singlechild Scroll view Here
        children: [
          StreamBuilder<QuerySnapshot>(
            stream: db.collection('Exercises').snapshots(),
            builder: (context, snapshot) {
              if (!snapshot.hasData) {
                return Center(
                  child: CircularProgressIndicator(),
                );
              } else
                return ListView(
                  children: (snapshot.data! as QuerySnapshot).docs.map((doc) {
                    return Card(
                      child: ListTile(
                        title: Text(doc.data()['name']),
                      ),
                    );
                  }).toList(),
                );
            },
          ),
        ],
      ),
    );
  }
}