Flutter Expanded で幅をいい感じに調整！！

まずは完成のコード

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Container(
          child: Row(
            children: <Widget>[
              Expanded(
                child: Container(
                  color: Colors.blue,
                ),
              ),
              Expanded(
                child: Container(
                  color: Colors.brown,
                ),
              ),
              Expanded(
                child: Container(
                  color: Colors.grey,
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

flex: で思い通りの幅に分ける

1:2:3で分けてみました！！

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Container(
          child: Row(
            children: <Widget>[
              Expanded(
                flex: 1,
                child: Container(
                  color: Colors.blue,
                ),
              ),
              Expanded(
                flex: 2,
                child: Container(
                  color: Colors.brown,
                ),
              ),
              Expanded(
                flex: 3,
                child: Container(
                  color: Colors.grey,
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}