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import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'わかりやすい'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: SafeArea(
        child: Row(
          children: <Widget>[
            Expanded(
              child: Container(
                padding: EdgeInsets.all(20.0),
                child: Text("1"),
                color: Colors.grey,
              ),
            ),
            Expanded(
              child: Container(
                padding: EdgeInsets.all(20.0),
                child: Text("2"),
                color: Colors.red,
              ),
            ),
            Expanded(
              child: Container(
                padding: EdgeInsets.all(20.0),
                child: Text("3"),
                color: Colors.green,
              ),
            ),
            Expanded(
              child: Container(
                padding: EdgeInsets.all(20.0),
                child: Text("4"),
                color: Colors.blue,
              ),
            ),
          ],
        ),
      ),
    );
  }
}