Can't align TextField/Form to center when decreasing its width - flutter

Question

I am trying to change the width of the text field, while also keeping it centered, I found a way to decrease its sized by wrapping it in a sized box and setting the width, however that seems to make it unaligned to the center, and when I try to align it again with the Center() property or the Align() Property nothing works.
import 'package:flutter/material.dart';
import 'package:qr_flutter/qr_flutter.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({super.key});
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(),
home: Scaffold(body: MyCustomForm()),
debugShowCheckedModeBanner: false,
);
}
}
class MyCustomForm extends StatefulWidget {
const MyCustomForm({super.key});
#override
MyCustomFormState createState() {
return MyCustomFormState();
}
}
// Create a corresponding State class.
// This class holds data related to the form.
class MyCustomFormState extends State<MyCustomForm> {
// Create a global key that uniquely identifies the Form widget
// and allows validation of the form.
//
// Note: This is a GlobalKey<FormState>,
// not a GlobalKey<MyCustomFormState>.
final _formKey = GlobalKey<FormState>();
#override
Widget build(BuildContext context) {
// Build a Form widget using the _formKey created above.
return Form(
key: _formKey,
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
TextFormField(
validator: (value) {
if (value == null || value.isEmpty) {
return 'Please enter some text';
}
return null;
},
),
const SizedBox(
height: 10,
),
ElevatedButton(
onPressed: () {
if (_formKey.currentState!.validate()) {
ScaffoldMessenger.of(context).showSnackBar(
const SnackBar(content: Text('Processing Data')),
);
}
},
child: const Text('Submit'),
),
],
),
);
}
}

Answer 1

You need to wrap your column with SizedBox and set its width to screen size. now when you set width for textfield its look ok, like this:
SizedBox(
width: double.infinity,//<--- add this
child: Form(
key: _formKey,
child: Column()
...
)
full example:
SizedBox(
width: double.infinity,
child: Form(
key: _formKey,
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
SizedBox(
width: 200,
child: TextFormField(
validator: (value) {
if (value == null || value.isEmpty) {
return 'Please enter some text';
}
return null;
},
),
),
const SizedBox(
height: 10,
),
ElevatedButton(
onPressed: () {
if (_formKey.currentState!.validate()) {
ScaffoldMessenger.of(context).showSnackBar(
const SnackBar(content: Text('Processing Data')),
);
}
},
child: const Text('Submit'),
),
],
),
),
)

Answer 2

Try below code and set width of SizedBox double.infinity :
SizedBox(
width: double.infinity,
child: Form(
key: _formKey,
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
TextFormField(
validator: (value) {
if (value == null || value.isEmpty) {
return 'Please enter some text';
}
return null;
},
),
const SizedBox(
height: 10,
),
ElevatedButton(
onPressed: () {
if (_formKey.currentState!.validate()) {
ScaffoldMessenger.of(context).showSnackBar(
const SnackBar(content: Text('Processing Data')),
);
}
},
child: const Text('Submit'),
),
],
),
),
)

Answer 3

Actually when you wrap TextFormField inside SizedBox your column width also becomes exactly equal to the width you gave to the SizedBox. This is because the column's width depends on the widest child inside of it. That is why you are not able to align or center the TextFormField.
Just wrap your Column inside the Center widget and your column will take all the width available and the children will also align to the center.
Form(
child: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
SizedBox(
width: 100,
child: TextFormField(
validator: (value) {
if (value == null || value.isEmpty) {
return 'Please enter some text';
}
return null;
},
),
),
const SizedBox(
height: 10,
),
ElevatedButton(
onPressed: () {},
child: const Text('Submit'),
),
],
),
),
)