Flutter -如何在WebView中下载文件？

dependencies:
  flutter:
    sdk: flutter
  webview_flutter: ^2.0.0

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

class WebViewPage extends StatelessWidget {
  final String url;

  WebViewPage({required this.url});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('WebView'),
      ),
      body: WebView(
        initialUrl: url,
        javascriptMode: JavascriptMode.unrestricted,
      ),
    );
  }
}

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

class WebViewPage extends StatefulWidget {
  final String url;

  WebViewPage({required this.url});

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

class _WebViewPageState extends State<WebViewPage> {
  late WebViewController _webViewController;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('WebView'),
      ),
      body: WebView(
        initialUrl: widget.url,
        javascriptMode: JavascriptMode.unrestricted,
        onWebViewCreated: (controller) {
          _webViewController = controller;
        },
        navigationDelegate: (NavigationRequest request) {
          if (request.url.endsWith('.pdf')) {
            downloadFile(request.url);
            return NavigationDecision.prevent;
          }
          return NavigationDecision.navigate;
        },
      ),
    );
  }

  Future<void> downloadFile(String url) async {
    final directory = await getExternalStorageDirectory();
    final filePath = '${directory!.path}/file.pdf';
    final response = await http.get(Uri.parse(url));

    if (response.statusCode == 200) {
      final file = File(filePath);
      await file.writeAsBytes(response.bodyBytes);
      Fluttertoast.showToast(msg: '文件已下载至$filePath');
    } else {
      Fluttertoast.showToast(msg: '下载失败');
    }
  }
}