Flutter Provider报错：Bad state: 读取创建时抛异常的Provider

问题场景 #

跟随教程开发音乐播放器，完成视频8:56左右的实现步骤后，运行代码抛出上述错误。

相关代码 #

main.dart #

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:secondlife_mobile/model.dart';

void main() {
  runApp(
    MaterialApp(
      debugShowCheckedModeBanner: false,
      home: ChangeNotifierProvider(
          create: (context) => PlayerModel(), child: const PlayerApp()),
    ),
  );
}

class PlayerApp extends StatefulWidget {
  const PlayerApp({super.key});

  @override
  State<PlayerApp> createState() => _PlayerAppState();
}

class _PlayerAppState extends State<PlayerApp> with TickerProviderStateMixin {
  AnimationController? _controller;
  Animation? _waveAnim;
  Animation? _waveConstAmpAnim;
  late PlayerModel model;

  @override
  void initState() {
    super.initState();
    _controller =
        AnimationController(vsync: this, duration: const Duration(seconds: 20))
          ..addListener(() => setState(() {}));
    _waveAnim =
        Tween<double>(begin: 1, end: 1).animate(_controller! /*null safe*/);
    _waveConstAmpAnim = Tween<double>(begin: 0, end: 1).animate(CurvedAnimation(
        curve: Curves.easeInSine, parent: _controller! /*null safe*/));
    _controller!.forward(); //null safe 6:32
  }

  @override
  Widget build(BuildContext context) {
    final height = MediaQuery.of(context).size.height;
    final width = MediaQuery.of(context).size.width;
    model = Provider.of<PlayerModel>(context);
    return Scaffold(
      body: Stack(
        children: <Widget>[
          Positioned(
            height: height,
            width: width,
            child: Material(
              elevation: 16,
              color: const Color(0xFFd6dde5), //Background Color
              borderRadius: BorderRadius.circular(20),
              child: Padding(
                padding: const EdgeInsets.symmetric(
                  horizontal: 30.0,
                ),
                child: Column(
                  children: <Widget>[
                    const SizedBox(
                      height: 90,
                    ),
                    const Text(
                      'Music title',
                    ),
                    const SizedBox(
                      height: 15,
                    ),
                    const Text(
                      'Music artist',
                    ),
                    const SizedBox(
                      height: 75,
                    ),
                    buildRecordPlayer(),
                    const SizedBox(
                      height: 60,
                    ),
                    Row(
                      children: const <Widget>[
                        Text('time'),
                        SizedBox(
                          width: 8,
                        ),
                        /*buildWave(width),*/
                        SizedBox(
                          width: 8,
                        ),
                        Text('end'),
                      ],
                    )
                  ],
                ),
              ),
            ),
          )
        ],
      ),
    );
  }

  Widget buildRecordPlayer() {
    return Container(
      height: 270,
      width: 270,
      alignment: Alignment.center,
      decoration: const BoxDecoration(
        image: DecorationImage(
          image: AssetImage('assets/images/vinyl.png'),
          fit: BoxFit.fitHeight,
          colorFilter: ColorFilter.mode(
            Colors.blue,
            BlendMode.color,
          ),
        ),
        shape: BoxShape.circle,
      ),
      child: ClipOval(
        child: Image.asset(
          'assets/images/SL.png',
          height: 165,
          width: 165,
          fit: BoxFit.fill,
        ),
      ),
    );
  }
}

model.dart #

import 'dart:math';

import 'package:flutter/material.dart';
import 'musicdata.dart';

class PlayerModel extends ChangeNotifier {
  List<Music> musicList = [];
  int _currentTrack = 0;

  PlayerModel() {
    for (int i = 0; i < Data.nameList.length; i++) {
      musicList
          .add(Music(artistName: Data.artistList[i], name: Data.nameList[i]));
    }

    musicList.removeWhere(
      (musicItem) => musicItem.name == null || musicItem.artistName == null,
    );

    for (var musicItem in musicList) {
      musicItem.duration = Duration(
        minutes: Random().nextInt(5).clamp(1, 5),
        seconds: Random().nextInt(59),
      );
    }

    for (var music in musicList) {
      print(music.name);
    }
  }

  int get currentTrack => _currentTrack;

  set currentTrack(int currentTrack) {
    _currentTrack = currentTrack;
    notifyListeners();
  }

  resetList() {
    for (var music in musicList) {
      music.isPlaying = false;
    }
  }
}

class Music {
  String? name;
  String? artistName;
  Duration? duration;
  bool? isPlaying = false;
  Music({this.duration, this.artistName, this.isPlaying, this.name});
}

报错信息 #

• 无调试运行时界面：
  
• 调试时错误提示：
  
• 调试控制台日志：
  
  

问题排查与解决 #

从调试控制台的错误栈可以看出，异常发生在PlayerModel的构造函数中，根源是**musicdata.dart中的Data类未正确定义，或者其中的nameList、artistList静态列表为空/未初始化**，导致访问Data.nameList.length时抛出空指针相关异常，进而导致Provider创建实例失败。

解决步骤 #

1. 创建或完善musicdata.dart文件，定义包含有效静态列表的Data类：

class Data {
  // 示例歌曲名列表，可根据需求修改
  static List<String> nameList = [
    "City Lights",
    "Ocean Waves",
    "Mountain Echo"
  ];

  // 对应歌曲的歌手列表，需保证与nameList长度一致
  static List<String> artistList = [
    "Electro Band",
    "Acoustic Duo",
    "Rock Collective"
  ];
}

2. 确保nameList和artistList长度相同，避免循环时出现索引越界问题。
3. 重新运行项目，此时PlayerModel可以正常初始化，Provider的创建错误会被修复。

额外优化（可选） #

在PlayerModel构造函数中添加校验逻辑，增强代码健壮性：

PlayerModel() {
  // 先校验列表有效性
  if (Data.nameList.isEmpty || 
      Data.artistList.isEmpty || 
      Data.nameList.length != Data.artistList.length) {
    throw Exception("歌曲列表或歌手列表为空，或两者长度不匹配");
  }
  // 原有初始化逻辑
  for (int i = 0; i < Data.nameList.length; i++) {
    musicList.add(Music(artistName: Data.artistList[i], name: Data.nameList[i]));
  }
  // ...其他代码
}

内容的提问来源于stack exchange，提问作者loupdaniel