How To Use Layout Builder Widget Using Flutter App

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.red,
      ),
      home: MyHomePage(),
    );
  }
}
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(
      backgroundColor: Colors.black,
      appBar: AppBar(
        backgroundColor: Colors.yellow[700],
          title: Text("Layout Builder Widget")),
      body: LayoutBuilder(
        builder: (context, constraints) {
          if (constraints.maxWidth > 600) {
            return _buildTwoContainers();
          } else {
            return _buildOneContainer();
          }
        },
      ),
    );
  }

  Widget _buildOneContainer() {
    return Center(
      child: Container(
        height: 200.0,
        width: 200.0,
        color: Colors.pink,
      ),
    );
  }

  Widget _buildTwoContainers() {
    return Center(
      child: Row(
        mainAxisAlignment: MainAxisAlignment.spaceAround,
        children: <Widget>[
          Container(
            height: 200.0,
            width: 200.0,
            color: Colors.green,
          ),
          Container(
            height: 200.0,
            width: 200.0,
            color: Colors.pink,
          ),
        ],
      ),
    );
  }
}