WebView showing ERR_CONNECTION_REFUSED (using flutter) - flutter

Question

I got this error while using webview in flutter.
error: ERR_CONNECTION_REFUSED
Here is my code:
import 'dart:async'; import 'dart:io';
import 'package:flutter/material.dart'; import 'package:webview_flutter/webview_flutter.dart'; import 'package:flutter/services.dart'; import 'package:mime/mime.dart'; import 'package:provider/provider.dart';
import 'package:num_plus_plus/src/backend/mathmodel.dart'; import 'package:num_plus_plus/src/pages/settingpage.dart';
class Server { class from inAppBrowser
late HttpServer _server;
int _port = 8080;
Server({int port = 8080}) { this._port = port; }
///Closes the server. Future<void> close() async { if (this._server != null) { await this._server.close(force: true); print('Server running on http://localhost:$_port closed'); this._server = null as HttpServer;
} }
Future<void> start() async { if (this._server != null) { throw Exception('Server already started on http://localhost:$_port');
}
var completer = new Completer(); runZoned(() { HttpServer.bind('127.0.0.1', _port, shared: true).then((server) { print('Server running on http://localhost:' + _port.toString());
this._server = server;
server.listen((HttpRequest request) async { var body = <int>[]; var path = request.requestedUri.path; path = (path.startsWith('/')) ? path.substring(1) : path; path += (path.endsWith('/')) ? 'index.html' : '';
try { body = (await rootBundle.load(path)).buffer.asUint8List(); catch (e) { print(e.toString()); request.response.close(); return;
}
var contentType = ['text', 'html']; if (!request.requestedUri.path.endsWith('/') && request.requestedUri.pathSegments.isNotEmpty) { var mimeType = lookupMimeType(request.requestedUri.path, headerBytes: body); if (mimeType != null) { contentType = mimeType.split('/');
}
}
request.response.headers.contentType = new ContentType(contentType[0], contentType[1], charset: 'utf-8'); request.response.add(body); request.response.close();
});
completer.complete();
}); onError: (e, stackTrace) => print('Error: $e $stackTrace'));
return completer.future; } }
class MathBox extends StatelessWidget { #override Widget build(BuildContext context) { final mathBoxController = Provider.of<MathBoxController>(context, listen: false); final mathModel = Provider.of<MathModel>(context, listen: false); final matrixModel = Provider.of<MatrixModel>(context, listen: false); final functionModel = Provider.of<FunctionModel>(context, listen: false); final mode = Provider.of<CalculationMode>(context, listen: false); return Stack( children: <Widget>[ WebView( onWebViewCreated: (controller) { controller.loadUrl("http://localhost:8080/assets/html/homepage.html"); mathBoxController.webViewController = controller;
}, onPageFinished: (s) { final setting = Provider.of<SettingModel>(context, listen: false); if (setting.initPage == 1) { mathBoxController.addExpression('\\\\bmatrix');
}
}, javascriptMode: JavascriptMode.unrestricted, javascriptChannels: Set.from([ JavascriptChannel( name: 'latexString', onMessageReceived: (JavascriptMessage message) { if (mode.value == Mode.Matrix) { matrixModel.updateExpression(message.message); else { if (message.message.contains(RegExp('x|y'))) { mode.changeMode(Mode.Function); functionModel.updateExpression(message.message); else { mode.changeMode(Mode.Basic); mathModel.updateExpression(message.message); mathModel.calcNumber();
}
}
}
), JavascriptChannel( name: 'clearable', onMessageReceived: (JavascriptMessage message) { mathModel.changeClearable(message.message == 'false'?false:true);
}
),
]),
), ClearAnimation(),
],
); } }
class ClearAnimation extends StatefulWidget { #override
_ClearAnimationState createState() => _ClearAnimationState(); }
class _ClearAnimationState extends State<ClearAnimation> with TickerProviderStateMixin {
late AnimationController animationController; late Animation animation;
#override void initState() { super.initState(); animationController = AnimationController(duration: const Duration(milliseconds: 500),vsync: this); final curve = CurvedAnimation(parent: animationController, curve: Curves.easeInOutCubic); animation = Tween<double>(begin: 0, end: 2000).animate(curve); Provider.of<MathBoxController>(context, listen: false).clearAnimationController = animationController; }
#override void dispose() { animationController.dispose(); super.dispose(); }
Widget _buildAnimation(BuildContext context, Widget? child) { return Positioned( top: 10-animation.value/2 as double, right: -animation.value/2, child: ClipOval( child: Container( height: animation.value, width: animation.value, color: Colors.blue[100],
),
),
); }
#override Widget build(BuildContext context) { return AnimatedBuilder( builder: _buildAnimation, animation: animation,
); } }
class MathBoxController {
late WebViewController _webViewController; late AnimationController clearAnimationController;
set webViewController(WebViewController controller) { this._webViewController = controller; }
void addExpression(String msg, {bool isOperator = false}) { assert(_webViewController != null);
_webViewController.evaluateJavascript("addCmd('$msg', {isOperator: ${isOperator.toString()}})"); }
void addString(String msg) { assert(_webViewController != null);
_webViewController.evaluateJavascript("addString('$msg')"); }
void equal() { assert(_webViewController != null);
_webViewController.evaluateJavascript("equal()"); }
void addKey(String key) { assert(_webViewController != null);
_webViewController.evaluateJavascript("simulateKey('$key')"); }
void deleteExpression() { assert(_webViewController != null);
_webViewController.evaluateJavascript("delString()"); }
void deleteAllExpression() { assert(_webViewController != null);
_webViewController.evaluateJavascript("delAll()"); }
}