Flutter App: XylophoneApp - Functions, Flutter Packages, Music player

 XylophoneApp 

import 'package:flutter/material.dart';
import 'package:audioplayers/audio_cache.dart';

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

class XylophoneApp extends StatelessWidget {
  Expanded buildKey({Color color, int soundNum}) {
    return (Expanded(
      child: FlatButton(
          onPressed: () {
            final player = AudioCache();
            player.play('note$soundNum.wav');
          },
          color: color),
    ));
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        backgroundColor: Colors.black,
        body: SafeArea(
          child: Column(
            mainAxisSize: MainAxisSize.max,
            crossAxisAlignment: CrossAxisAlignment.stretch,
            children: [
              buildKey(color: Colors.red, soundNum: 1),
              buildKey(color: Colors.orange, soundNum: 2),
              buildKey(color: Colors.yellow, soundNum: 3),
              buildKey(color: Colors.green, soundNum: 4),
              buildKey(color: Colors.teal, soundNum: 5),
              buildKey(color: Colors.blue, soundNum: 6),
              buildKey(color: Colors.purple, soundNum: 7)
            ],
          ),
        ),
      ),
    );
  }
}