Basic

sample.packages.flutter.lib.src.widgets.basic.2770.

This sample shows a [FractionallySizedBox] whose one child is 50% of the box's size per the width and height factor parameters, and centered within that box by the alignment parameter.

  
import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Scaffold(
        appBar: AppBar(title: const Text(_title)),
        body: const MyStatelessWidget(),
      ),
    );
  }
}

class MyStatelessWidget extends StatelessWidget {
  const MyStatelessWidget({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SizedBox.expand(
      child: FractionallySizedBox(
        widthFactor: 0.5,
        heightFactor: 0.5,
        alignment: FractionalOffset.center,
        child: DecoratedBox(
          decoration: BoxDecoration(
            border: Border.all(
              color: Colors.blue,
              width: 4,
            ),
          ),
        ),
      ),
    );
  }
}