我已经导入了audioplayer.dart，但它仍然向我显示错误：没有为类“_HomePageState”定义获取器“AudioPlayerState "

import 'package:audioplayers/audioplayers.dart';
_audioPlayer.onPlayerStateChanged.listen((event) {
  if (event == AudioPlayerState.PLAYING) {
    _isPlaying = true;
  } else {
    _isPlaying = false;
  }
  setState(() {});
});