setState((){}); is not updating Android Emulator - flutter

Question

I have a question about updating Android Emulator after pressing on an icon using setState()
this is my code:
import 'package:flutter/material.dart';
void main() {
return runApp(
MaterialApp(
home: Scaffold(
backgroundColor: Colors.red,
appBar: AppBar(
title: Text('Dicee'),
backgroundColor: Colors.red,
),
body: DicePage(),
),
),
);
}
class DicePage extends StatefulWidget {
#override
_DicePageState createState() => _DicePageState();
}
class _DicePageState extends State<DicePage> {
#override
Widget build(BuildContext context) {
int leftDiceNumber = 1;
return Center(
child: Row(
children: [
Expanded(
child: TextButton(
onPressed: () {
setState(() {
leftDiceNumber = 5;
});
},
child: Image.asset('images/dice$leftDiceNumber.png'),
),
),
Expanded(
child: TextButton(
onPressed: () {
print('Right button got pressed.');
},
child: Image.asset('images/dice2.png'),
),
),
],
),
);
}
}
and I tried even multiple choices that I found in Stackoverflow , but nothing it's working...
this.setState(() {
leftDiceNumber = 5;
});
WidgetsBinding.instance.addPostFrameCallback((_) => setState(...));
insted of just setState() and didn't work
I want to change the value of leftDiceNumber = 5 when I click on the picture
the initialised value for leftDiceNumber is 1

Answer 1

Put the variable outside the build method.leftDiceNumber, else it will reset on every build.
class DicePage extends StatefulWidget {
#override
_DicePageState createState() => _DicePageState();
}
class _DicePageState extends State<DicePage> {
int leftDiceNumber = 1; //here
#override
Widget build(BuildContext context) {
return Center(
child: Row(
children: [
Expanded(
child: TextButton(
onPressed: () {
setState(() {
leftDiceNumber = 5;
});
},
child: Image.asset('images/dice$leftDiceNumber.png'),
),
),
Expanded(
child: TextButton(
onPressed: () {
print('Right button got pressed.');
},
child: Image.asset('images/dice2.png'),
),
),
],
),
);
}
}