webview_flutter package - Unable to establish connection on channel. error - flutter

Question

I am trying to do WebView action with flutter_webview package. However, I am getting an error like this:
E/flutter (21358): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: PlatformException(error, java.lang.IllegalStateException: Trying to create a platform view of unregistered type: plugins.flutter.io/webview
Codes:
import 'package:flutter/material.dart';
import 'package:webview_flutter/webview_flutter.dart';
class ShelterMapPage extends StatefulWidget {
const ShelterMapPage({super.key});
#override
State<ShelterMapPage> createState() => _ShelterMapPageState();
}
final controller = WebViewController()
..setJavaScriptMode(JavaScriptMode.unrestricted)
..setBackgroundColor(const Color(0x00000000))
..setNavigationDelegate(
NavigationDelegate(
onProgress: (int progress) {
// Update loading bar.
},
onPageStarted: (String url) {},
onPageFinished: (String url) {},
onWebResourceError: (WebResourceError error) {},
onNavigationRequest: (NavigationRequest request) {
if (request.url.startsWith('https://www.youtube.com/')) {
return NavigationDecision.prevent;
}
return NavigationDecision.navigate;
},
),
)
..loadRequest(Uri.parse('https://flutter.dev'));
class _ShelterMapPageState extends State<ShelterMapPage> {
#override
Widget build(BuildContext context) {
return Scaffold(body: WebViewWidget(controller: controller));
}
}
Why am I getting an error and how can I solve it? Thanks for help.