如何在flutter中从app + web中的URL下载图片？

import 'dart:io';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'package:path_provider/path_provider.dart';

class ImageDownloader extends StatefulWidget {
  final String imageUrl;

  ImageDownloader({required this.imageUrl});

  @override
  _ImageDownloaderState createState() => _ImageDownloaderState();
}

class _ImageDownloaderState extends State<ImageDownloader> {
  bool downloading = false;
  String? imagePath;

  Future<void> downloadImage() async {
    setState(() {
      downloading = true;
    });

    var response = await http.get(Uri.parse(widget.imageUrl));
    var documentDirectory = await getApplicationDocumentsDirectory();
    var filePath = '${documentDirectory.path}/image.jpg';
    File file = File(filePath);
    await file.writeAsBytes(response.bodyBytes);

    setState(() {
      downloading = false;
      imagePath = filePath;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Image Downloader'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            if (downloading)
              CircularProgressIndicator()
            else if (imagePath != null)
              Image.file(File(imagePath!))
            else
              Text('Click the button to download image'),
            SizedBox(height: 20),
            ElevatedButton(
              onPressed: downloadImage,
              child: Text('Download Image'),
            ),
          ],
        ),
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(
    home: ImageDownloader(
      imageUrl: 'https://example.com/image.jpg',
    ),
  ));
}

dependencies:
  flutter:
    sdk: flutter
  http: ^0.13.3
  path_provider: ^2.0.5