Flutter showDialog with return value

main.dart

import 'package:flutter/material.dart';

final Color darkBlue = Color.fromARGB(255, 18, 32, 47);

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.light().copyWith(scaffoldBackgroundColor: darkBlue),
      debugShowCheckedModeBanner: false,
      home: Home(),
    );
  }
}

class Home extends StatefulWidget {
  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> {
  TextEditingController _controller = TextEditingController();
  String inputString = "";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(inputString),
            ElevatedButton(
              child: Text("Show Dialog"),
              onPressed: () {
                showDialog(
                  context: context,
                  builder: (BuildContext context) {
                    return AlertDialog(
                      title: Text("Setting String"),
                      content: TextFormField(
                        controller: _controller,
                      ),
                      actions: <Widget>[
                        TextButton(
                          child: Text("OK"),
                          onPressed: () {
                            Navigator.pop(context, _controller.text);
                          },
                        )
                      ],
                    );
                  },
                ).then((val) {
                  setState(() {
                    inputString = val;
                  });
                });
              },
            ),
          ],
        ),
      ),
    );
  }
}

DartPad Demo: dartpad.dev/?id=472f481cb95c2c58d4558f6b7d1c414c.
Based on Dart SDK 3.4.4 and Flutter SDK 3.22.3