Slider widget does not work on iOS and Web - flutter

Question

I have an audio player in my app. I used Slider.adaptive to make the seek bar. Although It works well on Android, it gives me this error on iOS and the Web:
════════ Exception caught by widgets library
═══════════════════════════════════ Assertion failed:
../…/cupertino/slider.dart:332 value != null && value >= 0.0 && value
<= 1.0 is not true
The relevant error-causing widget was Slider
Here is how my code looks like:
class PlayBackButtons extends StatefulWidget {
#override
_PlayBackButtonsState createState() => _PlayBackButtonsState();
}
class _PlayBackButtonsState extends State<PlayBackButtons> {
bool _isPlaying = false;
AudioPlayer _audioPlayer;
Duration _duration = new Duration();
Duration _position = new Duration();
int result = 0;
int tutsLenght;
int index;
#override
void initState() {
super.initState();
_audioPlayer = AudioPlayer();
Future.delayed(Duration.zero, () {
Provider.of<Tutorials>(context, listen: false).resetIndex();
});
}
#override
void dispose() {
_cleanup();
super.dispose();
}
double progress() => max() > (_position?.inMilliseconds ?? 0).toDouble()
? (_position?.inMilliseconds ?? 0).toDouble()
: 0.0;
double max() => (_duration.inMilliseconds ?? 0.0).toDouble();
void _cleanup() {
if (result == 1) {
_audioPlayer.stop();
_audioPlayer.dispose();
Provider.of<Tutorials>(context).resetIndex();
}
}
void _play(String url) async {
result = await _audioPlayer.play(url);
setState(() => _isPlaying = true);
if (result == 1) {
_audioPlayer.onDurationChanged.listen((Duration dd) {
setState(() {
_duration = dd;
});
});
_audioPlayer.onAudioPositionChanged.listen((Duration dd) {
setState(() {
_position = dd;
});
});
} else {
print('audio player crashed');
}
}
void _pause() async {
await _audioPlayer.pause();
setState(() => _isPlaying = false);
}
void _next() async {
await _audioPlayer.stop();
setState(() => _isPlaying = false);
if (Provider.of<Tutorials>(context).index < tutsLenght) {
} else {
Navigator.pop(context);
}
}
void _previous() {
if (Provider.of<Tutorials>(context).index != 0) {
_audioPlayer.stop();
setState(() => _isPlaying = false);
Provider.of<Tutorials>(context).decrementIndex();
}
}
#override
Widget build(BuildContext context) {
index = Provider.of<Tutorials>(context).index;
final tuts = Provider.of<Tutorials>(context, listen: false).tutsOfASection;
tutsLenght = tuts.length;
final url = tuts[index].audio;
return Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Slider.adaptive(
min: 0.0,
value: progress(),//_position.inSeconds.toDouble(),
max: max(),//_duration.inSeconds.toDouble(),
onChanged: (double value) {
setState(() => _audioPlayer.seek(Duration(seconds: value.toInt())));
},
),
Row(
children: [
IconButton(
icon: Icon(Icons.skip_previous),
onPressed: () => _previous(),
),
IconButton(
icon: _isPlaying ? Icon(Icons.pause) : Icon(Icons.play_arrow),
onPressed: () {
if (_isPlaying) {
_pause();
} else {
_play(url);
}
},
),
IconButton(
icon: Icon(Icons.skip_next),
onPressed: () => _next(),
),
],
mainAxisAlignment: MainAxisAlignment.center,
),
],
);
}
}