Align text in centre of screen - flutter

Question

I am trying to use Expand widget in Column so user can tap in any position of screen to increase counter, but there is an issue in alignment of text in crossAxisAlignment and mainAxisAlignment of the column it didn't apply on Expand widget as the following
return MaterialApp(
home: Scaffold(
backgroundColor: Colors.black12,
body: SafeArea(
child: Center(
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Expanded(
child: GestureDetector(
onTap: () {
setState(() {
i++;
print(i);
});
},
child: Text(
i.toString(),
style: TextStyle(fontSize: 50.0, color: Colors.blueAccent),
textAlign: TextAlign.center,
),
),
),
],
),
),
),
),
);

Answer 1

You went with the wrong approach because you can't Center an Expanded because Expanded takes the entire available space inside Row or Column in your case Column with single Widget inside children the GestureDetector. Here is one of a solution for what you want to achieve
#override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Colors.black12,
body: SafeArea(
child: Center(
child: Stack(
children: <Widget>[
Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Expanded(
child: GestureDetector(
onTap: () {
setState(() => i++;);
},
),
),
],
),
Align(
alignment: Alignment.center,
child: Text(
'$i',
style: TextStyle(fontSize: 50.0, color: Colors.blueAccent),
),
),
],
),
),
),
);
}

Answer 2

another solution using FlatButton inside SizedBox.expand()
so you don't need to fight with a single child column.
class _MyAppState extends State<MyApp> {
int i = 0;
#override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
backgroundColor: Colors.black12,
body: SafeArea(
child: SizedBox.expand(
child: FlatButton(
onPressed: () {
setState(() {
i++;
print(i);
});
},
child: Text(
i.toString(),
style: TextStyle(fontSize: 50.0, color: Colors.blueAccent),
),
),
),
),
),
);
}
}