[Flutter] How to use basic features of web view

custom_webview.dart

 Future<void> _showDemoPage(BuildContext context, String url) async {
    final parameters = await Navigator.of(context).push(
      MaterialPageRoute(
        builder: (context) => CustomWebView(
          initialUrl: url,
        ),
      ),
    );

    print('AppHome: _showDemoPage: parameters: $parameters');
  }
}

class CustomWebView extends StatefulWidget {
  final String initialUrl;

  const CustomWebView({Key key, this.initialUrl}) : super(key: key);

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

class _CustomWebViewState extends State<CustomWebView> {
  bool _showProgress = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: SingleChildScrollView(
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: [
              Offstage(
                offstage: !_showProgress,
                child: LinearProgressIndicator(),
              ),
              SizedBox(
                height: 800,
                child: buildWebView(),
              ),
            ],
          ),
        ),
      ),
    );
  }

  Widget buildWebView() {

    return InAppWebView(
      initialUrlRequest: URLRequest(
        url: Uri.parse(widget.initialUrl),
      ),
      onLoadStart: (controller, url) => _onPageStart(url.toString()),
      onLoadStop: (controller, url) => _onPageFinish(url.toString()),
      gestureRecognizers: <Factory<OneSequenceGestureRecognizer>>[
        Factory<OneSequenceGestureRecognizer>(
          () => HorizontalDragGestureRecognizer(),
        ),
      ].toSet(),
    );
  }

  void setProgressBar(bool status) {
    setState(() => _showProgress = status);
  }

  void _onPageStart(String url) {
    print('_CustomWebViewState: _onPageStart: url: $url');
    
    // [optional] method to extract data from current url
    // final params = _extractParams(url);
    // Navigator.of(context).pop(params);

    
    setProgressBar(true);
  }

  void _onPageFinish(String url) {
    print('_CustomWebViewState: _onPageFinish: url: $url');
    setProgressBar(false);
  }

  // method to extract parameters from current url
  _extractParams(String url) {
    final paramString = url.substring(url.indexOf('?') + 1);

    final params = {};
    paramString.split('&').forEach((String _param) {
      final entry = _param.split('=');
      final key = entry[0];
      final value = entry[1];
      params[key] = value;
    });

    print('_CustomWebViewState: _onPageFinish: params: $params');
    return params;
  }
}