Flutter cupertinoPicker value not changing

I'm trying to use CupertinoPicker on a AlertDialog widget but the values are do not change. The same code work when it's not the AlertDialog widget. What's happening?

Button to press to show AlertDialog:

ElevatedButton(
 onPressed: () {

showDialog(
context: context, builder: (context) => AlertDialog(
content:Builder(builder: (context) {
return SizedBox(
child: Column(
children: [
....

]
)
)
}
)
)
}
)

One of the children is the CupertinoWidget and this is the code:

In the class widget int selectedValue = 0;

CupertinoButton.filled(child: Text('$selectedValue'),
onPressed: () =>showCupertinoModalPopup(context:context,builder: (_) =>
SizedBox(width:screenWidth *0.3,height:screenHeight *0.25,
child:CupertinoPicker(backgroundColor:Colors.white,
itemExtent:30,
scrollController:FixedExtentScrollController(initialItem: 1),
children: const [Text('0'),
                 Text('1'),
                 Text('2'),
                 Text('3'),
                 Text('4'),
                 Text('5'),
                 Text('6'),
                 Text('7'),
                 ],
onSelectedItemChanged:(intvalue) {
    setState(() {selectedValue =value;
                                                                          });
                                                                        },
                                                                      ),
                                                                    ),
                                                                  ),
                                                                ),

With this the value in Text('$selectedValue') do not change. But when I write the same code on a new Scaffold screen it works perfectly. Any reason?

create a separate StatefullWidget for AlertDialog:

ElevatedButton(
 onPressed: () {

showDialog(
context: context, builder: (context) => Dialog()
)
}
)




class Dialog extends StatefulWidget {
  const Dialog({super.key});

  @override
  State<Dialog> createState() => _DialogState();
}

class _DialogState extends State<Dialog> {
  @override
  Widget build(BuildContext context) {
    return AlertDialog(content: Builder(builder: (context) {
      return SizedBox(child: Column(children: []));
    }));
  }
}

You can also use statefulBuilder instead of builder so you will be able to change state inside AlertDialog:

 showDialog(
            context: context,
            builder: (context) => AlertDialog(content: StatefulBuilder(
                  builder: ((context, setState) {
                    return Column();
                  }),
                )))

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primaryColor: Colors.indigo,
        useMaterial3: true,
      ),
      home: const MyHomePage(),
    );
  }
}

int currentValue = 0;
DateTime date = DateTime(DateTime.april);

//use stateful widget when you want to change state
class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key});

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        children: [
          //button to show dialog
          ElevatedButton(
            child: Text("show Dialog "),
            onPressed: () {
              showDialog(context: context, builder: (context) => Dialog());
            },
          ),
        ],
      ),
    );
  }
}

class Dialog extends StatefulWidget {
  Dialog({super.key});

  @override
  State<Dialog> createState() => _DialogState();
}

class _DialogState extends State<Dialog> {
  @override
  Widget build(BuildContext cont) {
    return SizedBox(
      height: 200,
      child: AlertDialog(
        content: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            Padding(
              padding: const EdgeInsets.all(8.0),
              child: Text("$currentValue"),
            ),
            Text('$date'),
            Padding(
              padding: const EdgeInsets.all(8.0),
              child: SizedBox(
                height: 30,
                child: CupertinoPicker(
                  scrollController:
                      FixedExtentScrollController(initialItem: currentValue),
                  itemExtent: 30,
                  children: [
                    Text('0'),
                    Text('1'),
                    Text('2'),
                    Text('3'),
                    Text('4'),
                    Text('5'),
                    Text('6'),
                    Text('7'),
                    Text('8'),
                    Text('9'),
                  ],
                  onSelectedItemChanged: (newValue) {
                    setState(() {
                      currentValue = newValue;
                    });
                  },
                ),
              ),
            ),
            SizedBox(
              height: 200,
              child: CupertinoDatePicker(onDateTimeChanged: (newDate) {
                setState(() {
                  print(date);
                  print(newDate);
                  date = newDate;
                });
              }),
            ),
          ],
        ),
      ),
    );
  }
}