How to make row/column of non-fixed sized parent fill the whole space - flutter

Question

I am trying to do it with Expanded but I am getting 'RenderFlex children have non-zero flex but incoming width constraints are unbounded.' which is expected because the size of parent is not defined.
Row(
mainAxisSize: MainAxisSize.max,
children: <Widget>[
Text(
'something',
style: Theme.of(context).primaryTextTheme.headline2,
),
Expanded(
child: Container(),
),
]
)

Answer 1

If your Row is wrapped within an Column widget it will take up all of the available space and give your Row the required Parent width. This will be rendered at the top of the Column.
import 'package:flutter/material.dart';
class TestScreen extends StatelessWidget {
static const routeName = '/testScreen';
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Test'),
),
body: Column(
children: <Widget>[
Row(
mainAxisSize: MainAxisSize.max,
children: <Widget>[
Text(
'something',
style: Theme.of(context).primaryTextTheme.headline2,
),
Expanded(
child: Container(),
),
],
),
],
),
);
}
}
If you want the widget to take up entire height as well then wrap it again with an Expanded
import 'package:flutter/material.dart';
class TestScreen extends StatelessWidget {
static const routeName = '/testScreen';
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Test'),
),
body: Column(
children: <Widget>[
Expanded(
child: Row(
mainAxisSize: MainAxisSize.max,
children: <Widget>[
Text(
'something',
style: Theme.of(context).primaryTextTheme.headline2,
),
Expanded(
child: Container(),
),
],
),
),
],
),
);
}
}
If you do not give the Row this fixed area it will expand indefinitely off the side of your screen
Non Column solution
body: SingleChildScrollView(
child: Row(
mainAxisSize: MainAxisSize.max,
children: <Widget>[
Text(
'something',
style: Theme.of(context).primaryTextTheme.headline2,
),
Expanded(
child: Container(),
),
],
),
),