Flutter DropdownButtonFormField setState does not work outside of onChanged method - flutter

Question

I just created a simple flutter app with two DropdownButtonFormField widgets.
And I want to update both widgets if first one is selected.
Expectation:
select number from the first dropdown menu
same number appears in the second dropdown
Result:
- select number from the first dropdown menu
- only the first dropdown menu is updated
Can somebody please tell me what I am doing wrong when calling setState onChaged method of the first dropdown menu widget?
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
debugShowCheckedModeBanner: false,
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
List<int> myList = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0];
int currentNumber = 1;
int anotherNumber = 9;
void _incrementCounter() {
setState(() {
_counter++;
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
DropdownButtonFormField<int>(
value: currentNumber,
items: myList.map((int value) {
return DropdownMenuItem<int>(
value: value,
child: Container(
width: 200,
child: Text(
value.toString(),
),
),
);
}).toList(),
onChanged: (int newValue) {
setState(() {
currentNumber = newValue;
anotherNumber = newValue;
});
},
),
DropdownButtonFormField<int>(
value: anotherNumber,
items: myList.map((int value) {
return DropdownMenuItem<int>(
value: value,
child: Container(
width: 200,
child: Text(
value.toString(),
),
),
);
}).toList(),
onChanged: (int newValue) {
setState(() {
anotherNumber = newValue;
});
},
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}}