How to Create a Progress Indicator for WebView in Flutter

import 'package:flutter/material.dart';
import 'package:webview_flutter/webview_flutter.dart';
 
void main() => runApp(MyApp());

class MyApp extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
    home: Scaffold(
        body: WebViewClass()
       )
      );
  }
}

class WebViewClass extends StatefulWidget {

  WebViewState createState() => WebViewState();

}

class WebViewState extends State<WebViewClass>{

  num position = 1 ;

  final key = UniqueKey();

  doneLoading(String A) {
    setState(() {
      position = 0;
    });
  }

  startLoading(String A){
    setState(() {
      position = 1;
    });
  }

  @override
  Widget build(BuildContext context) {
  return Scaffold(
     appBar: AppBar(
        title: Text('Show ProgressBar While Loading Webview')),
      body: IndexedStack(
      index: position,
      children: <Widget>[

      WebView(
        initialUrl: 'https://Google.com',
        javascriptMode: JavascriptMode.unrestricted,
        key: key ,
        onPageFinished: doneLoading,
        onPageStarted: startLoading,
        ),

       Container(
        color: Colors.white,
        child: Center(
          child: CircularProgressIndicator()),
        ),
        
      ])
  );
  }
}

Why is this error showing? Basically I want to add progress bar on flutter webview before loading the full website. After many searching I got this code but I also showing error. Is there any problem in this code or if you can, kindly help me with new code.

>Solution :

Follow this,

1. Replace num with int?, at line no 26 -> like, int? position = 1 ;
2. Add !(Exclamation mark) after position, at line no 48 -> like, index: position!.

Happy codding!