Flutter: setState does not update inner widget

I have a song playlist screen that includes a list of songs and a navbar for audio play/pause. I set the initial value of the song field as the first element of the songs list, however, when I update the selected song with setState(), the navbar does not update its song.

class Body extends StatefulWidget {
  @override
  BodyState createState() => BodyState();
}

class BodyState extends State<Body> {
  Music selectedSong = songs[0];
  ...
  @override
  Widget build(BuildContext context) {
    return Column(
       ...
       Expanded(
          child: ListView.builder(
          shrinkWrap: true,
          scrollDirection: Axis.vertical,
          padding: const EdgeInsets.only(top: 20),
          itemCount: songs.length,
          itemBuilder: (context, i) => songCard(songs[i])
       ...
       MusicBar(music: selectedSong)

For songCard() function:

 Widget songCard(Music item) {
    return ListTile(
      onTap: () => {
        setState(() {
          selectedSong = item;
        })
      },
     ...

When I debug the code, selectedSong field is updated as expected, however music field inside MusicBar is not updated.

For MusicBar class:

class MusicBar extends StatefulWidget {
  final Music music;
  const MusicBar({Key key, this.music}) : super(key: key);
  MusicBarState createState() => MusicBarState(music: music);
}

class MusicBarState extends State<MusicBar> {

  final Music music;
  MusicBarState({this.music});

  AudioPlayer player = AudioPlayer();

  @override
  void initState() {
    super.initState();
    // duration = music.duration;
    player.onDurationChanged.listen((updatedDuration) {
      setState(() {
        duration = updatedDuration;
      });
    });

    player.onAudioPositionChanged.listen((updatedPosition) {
        setState(() {
          position = updatedPosition;
        });
    });
  }

  @override
  void dispose(){
    super.dispose();
    player.stop();
    player.dispose();
  }
  
  @override
  Widget build(BuildContext context){
    return Container(
      ...

What did I do wrong so that the MusicBar widget is not updating? If needed, songs list is defined outside Body class, and I am using audioplayers library

Solution

In MusicBarState you can access to music field on Music using widget. You can refactor you State to:

class MusicBar extends StatefulWidget {
  final Music music;
  const MusicBar({Key key, this.music}) : super(key: key);
  MusicBarState createState() => MusicBarState(); // Empty constructor
}

class MusicBarState extends State<MusicBar> {
  // Remove this
  // final Music music;
  // MusicBarState({this.music});

 someMethod() {
   // You can access to music using widget:
   print(widget.music);
 }
 // ...
}

Test and check if now works