Flutter无法获取下载url firebase-storage

import 'package:firebase_storage/firebase_storage.dart';
import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Firebase Storage Demo',
      home: Scaffold(
        appBar: AppBar(
          title: Text('Firebase Storage Demo'),
        ),
        body: Center(
          child: ElevatedButton(
            onPressed: () {
              getDownloadUrl();
            },
            child: Text('Get Download URL'),
          ),
        ),
      ),
    );
  }

  void getDownloadUrl() async {
    Reference ref = FirebaseStorage.instance.ref().child('path/to/file.jpg');
    String downloadUrl = await ref.getDownloadURL();
    print('Download URL: $downloadUrl');
  }
}