First declare your musicplayer in .h file.
MPMusicPlayerController *musicPlayer;
in viewDidLoad
you can define it.
self.musicPlayer=[MPMusicPlayerController applicationMusicPlayer];
// musicPlayer.volume = 0.5f;
- (IBAction)sliderValueChanged : (UISlider *)sender
{
musicPlayer.volume=sender.value;
}
Try changing volume by giving static value then go for dynamic.