Flutter not showing CircularProgressIndicator - flutter

Question

I'm developing simple webview applicatoin using flutter , here i used CircularProgressIndicator but its not showing.
Package i use: https://pub.dev/packages/flutter_webview_plugin
How i can show the loading using CircularProgressIndicator in flutter ?, I'm using stack to show the loading indicator the centor of it.
class _MyHomePageState extends State<MyHomePage> {
final flutterWebViewPlugin = FlutterWebviewPlugin();
bool isLoading = true;
double webProgress = 0;
#override
void initState() {
super.initState();
flutterWebViewPlugin.onProgressChanged.listen((double progress) {
setState(() {
this.webProgress = progress;
});
print("The progress is $progress");
});
}
#override
Widget build(BuildContext context) {
return SafeArea(
child: Scaffold(
body: WillPopScope(
onWillPop: () async {
print("back pressed");
return false;
},
child: Stack(
children: [
Column(
children: [
webProgress < 1
? SizedBox(
height: 5,
child: LinearProgressIndicator(
value: webProgress,
color: Colors.blue,
backgroundColor: Colors.white,
),
)
: SizedBox(),
Expanded(
child: WebviewScaffold(
url: "https://google.com",
mediaPlaybackRequiresUserGesture: false,
withLocalStorage: true,
),
),
],
),
isLoading
? Center(
child: CircularProgressIndicator(
color: Colors.red,
),
)
: Stack(),
],
),
),
));
}
}