flutter_webview获取正在显示的页面的html，如何从get浏览页面中获取HTML？

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

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'WebView Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final flutterWebViewPlugin = FlutterWebviewPlugin();

  @override
  void initState() {
    super.initState();
    flutterWebViewPlugin.onStateChanged.listen((WebViewStateChanged state) {
      if (state.type == WebViewState.finishLoad) {
        flutterWebViewPlugin.evalJavascript('''
          javascript:(function() {
            var html = document.documentElement.innerHTML;
            window.flutter_inappwebview.callHandler('htmlContent', html);
          })();
        ''');
      }
    });
  }

  @override
  void dispose() {
    flutterWebViewPlugin.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return WebviewScaffold(
      url: 'https://example.com',
      appBar: AppBar(
        title: Text('WebView Demo'),
      ),
      withJavascript: true,
      withLocalStorage: true,
      hidden: true,
    );
  }
}