Is it possible to concatenate strings and variables in a Flutter 3 WebView URL?

I am creating a WebView page using Flutter 3, and I'm using webview_flutter: 4.2.2. The URL I'm using contains multiple parameters, so I need to use a dynamic URL. I've tried something like the following example, but there's an error in the loadRequest(Uri.parse(urlfull)) part.

Here's the complete code:
import 'dart:html';

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

class HomeTab extends StatefulWidget {
  const HomeTab({super.key});
  @override
  // ignore: library_private_types_in_public_api
  _HomeTabState createState() => _HomeTabState();
}

class _HomeTabState extends State<HomeTab> {
  late String urlfull;

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

  @override
  void initState() {
    super.initState();
    startLaunching();
    //untuk melakukan refresh tampilan
  }

  startLaunching() async {
    final prefs = await SharedPreferences.getInstance();
    final authUserId = prefs.getString("auth_user_id")!;
    String username = prefs.getString("username")!;
    final urlfull = baseUrl + "mobile/index?q=$authUserId&u=$username";
    setState(() {});
  }

  WebViewController controller = WebViewController()
    ..setJavaScriptMode(JavaScriptMode.unrestricted)
    ..setBackgroundColor(const Color(0x00000000))
    ..setNavigationDelegate(NavigationDelegate(
      onProgress: (int progress) {},
      onPageStarted: (String url) {},
      onPageFinished: (String url) {},
      onWebResourceError: (WebResourceError error) {},
    ))
    ..enableZoom(false)
    ..loadRequest(Uri.parse(urlfull));

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        debugShowCheckedModeBanner: false,
        home: Scaffold(
          body: WebViewWidget(controller: controller),
        ));
  }
}

I have tried editing in several ways in the loadRequest(Uri.parse(urlfull)) part, but it always displays "Extract Method".

You actually have two variables named urlfull. Within startLaunching you should probably remove "final" before urlfull so that you are updating your state variable urlfull instead of a new urlfull variable.

If you add dev_dependencies in your pubspec.yaml file for lint and flutter_lints your IDE will highlight potential errors like this one.