To show the review popup using initState() in a Flutter app using the in_app_review plugin, you can use the following code:

javaCopy code
import 'package:in_app_review/in_app_review.dart';

class YourStatefulWidget extends StatefulWidget {
  @override
  _YourStatefulWidgetState createState() => _YourStatefulWidgetState();
}

class _YourStatefulWidgetState extends State<YourStatefulWidget> {
  InAppReview inAppReview = InAppReview.instance;

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addPostFrameCallback((_) async {
      if (await inAppReview.isAvailable()) {
        inAppReview.requestReview();
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    // ...
  }
}

In this code, we are using the InAppReview instance to check if the review system is available on the current platform. If it is, we then use requestReview() to show the review popup to the user.

We are also using addPostFrameCallback() to ensure that the code is executed after the first frame is rendered, which is necessary for the InAppReview plugin to work correctly.