flutter获取js渲染后的html内容，拦截媒体文件

dependencies:
  flutter:
    sdk: flutter
  webview_flutter: ^4.0.0
  path_provider: ^2.0.11

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

class WebContentExtractor extends StatefulWidget {
  final String url;

  const WebContentExtractor({Key? key, required this.url}) : super(key: key);

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

class _WebContentExtractorState extends State<WebContentExtractor> {
  late WebViewController _controller;
  String? _htmlContent;
  List<String> _downloadedFiles = [];

  @override
  void initState() {
    super.initState();
    _controller = WebViewController()
      ..setJavaScriptMode(JavaScriptMode.unrestricted)
      ..setNavigationDelegate(
        NavigationDelegate(
          onPageFinished: (String url) {
            _extractContent();
          },
        ),
      )
      ..loadRequest(Uri.parse(widget.url));
  }

  Future<void> _extractContent() async {
    // 获取渲染后的HTML内容
    _htmlContent = await _controller.runJavaScriptReturningResult(
      "document.documentElement.outerHTML;"
    ) as String?;

    // 注入JavaScript以拦截网络请求
    await _controller.runJavaScript('''
      (function() {
        var originalFetch = window.fetch;
        window.fetch = function() {
          return originalFetch.apply(this, arguments).then(function(response) {
            var url = response.url;
            if (url.endsWith('.mp3') || url.endsWith('.mp4')) {
              window.flutter_inappwebview.callHandler('onResourceDetected', url);
            }
            return response;
          });
        };
      })();
    ''');

    // 添加JavaScript处理程序
    await _controller.addJavaScriptChannel(
      'flutter_inappwebview',
      onMessageReceived: (JavaScriptMessage message) {
        _downloadFile(message.message);
      },
    );

    setState(() {});
  }

  Future<void> _downloadFile(String url) async {
    try {
      final response = await HttpClient().getUrl(Uri.parse(url));
      final httpResponse = await response.close();
      final bytes = await consolidateHttpClientResponseBytes(httpResponse);
      final dir = await getApplicationDocumentsDirectory();
      final file = File('${dir.path}/${url.split('/').last}');
      await file.writeAsBytes(bytes);
      setState(() {
        _downloadedFiles.add(file.path);
      });
    } catch (e) {
      print('Error downloading file: $e');
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Web Content Extractor')),
      body: Column(
        children: [
          Expanded(
            child: WebViewWidget(controller: _controller),
          ),
          if (_htmlContent != null)
            Text('HTML content extracted (length: ${_htmlContent!.length})'),
          if (_downloadedFiles.isNotEmpty)
            Text('Downloaded files: ${_downloadedFiles.join(", ")}'),
        ],
      ),
    );
  }
}

WebContentExtractor(url: 'https://example.com')