这是一个基本的颤振音乐播放器应用程序。

main.dart

import 'package:flute_music_player/flute_music_player.dart';

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

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  List<Song> _songs;
  @override

  void initState() {
    // TODO: implement initState
    super.initState();
    initPlayer();
  }

  void initPlayer() async{
    var songs = await MusicFinder.allSongs();
    songs=new List.from(songs);
    setState(() {
      _songs = songs;
    });
  }


  @override

  Widget build(BuildContext context) {

      Widget home(){
        new Scaffold(
          appBar: new AppBar(title: new Text("Music App"),

          ),
          body: new ListView.builder(
              itemCount: _songs.length,
              itemBuilder: (context,int index){
                return new ListTile(
                  leading: new CircleAvatar(
                    child: new Text(_songs[index].title[0]),
                  ),
                  title: new Text(_songs[index].title),
                );
              }),
        );
      }



    return new MaterialApp(
      home: home(),
    );
  }
}

pubspec.yaml

name: music_player
description: A new Flutter application.
version: 1.0.0+1

environment:
  sdk: ">=2.1.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter
  cupertino_icons: ^0.1.2
  flute_music_player:

dev_dependencies:
  flutter_test:
    sdk: flutter
flutter:
  uses-material-design: true

它应该显示音乐列表，但会出现意外错误。我正在android上运行。请帮我。

Answer 1

将itemCount: _songs.length更改为itemCount: _songs?.length ?? 0-有助于避免出现异常情况

Answer 2

由于您正在执行异步操作，因此将花费一定的时间，因此在您的应用首次构建时，songs数组为null。尝试以空数组而不是空数组开始：List<Song> _songs = [];，然后，当异步操作完成时，setState将使小部件重新生成并显示包含数据的数组。

错误：对null调用了getter'length'

这是一个基本的颤振音乐播放器应用程序。

2 个答案: