why am i getting progress slider exception error - ios

Question

I am making an application which will play audio.I have used a slider to show the time elapsed and time remaining graphically in the slider.But i am not getting how to get the value programitcically.I have used the following code but its throwing an exception.
-(void) updateMyProgress
{
float progress = [avPlayer currentTime]/[avPlayer duration];
self.myProgressView.progress = progress;
}
The code im my viewcontoller.m file is
#import "ViewController.h"
#interface ViewController ()
{
AVAudioPlayer *avPlayer;
AVPlayer *avp;
}
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
NSString *stringPath = [[NSBundle mainBundle]pathForResource:#"naat" ofType:#"mp3"];
NSURL *url = [NSURL fileURLWithPath:stringPath];
NSError *error;
avPlayer = [[AVAudioPlayer alloc]initWithContentsOfURL:url error:&error];
[avPlayer setNumberOfLoops:2];
[avPlayer setVolume:self.sliderVolumeOutlet.value];
[NSTimer scheduledTimerWithTimeInterval:1 target:self selector:#selector(updateMyProgress) userInfo:nil repeats:YES];
}
/*-(void) updateMyProgress
{
CGFloat progress = [avPlayer currentTime]/[avPlayer duration];
self.myProgressView.progress = progress;
}
*/
-(void) updateMyProgress
{
AVPlayerItem *currentItem = avp.currentItem ;
CMTime duration = currentItem.duration; //total time
CMTime currentTime = currentItem.currentTime; //playing time
CGFloat progress = currentTime.value/duration.value;
self.myProgressView.progress = progress;
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
- (IBAction)sliderVolumeAction:(id)sender
{
UISlider *myslider= sender;
[avPlayer setVolume:myslider.value];
}
- (IBAction)stopButton:(id)sender
{
[avPlayer stop];
[avPlayer setCurrentTime:0];
}
- (IBAction)pauseButton:(id)sender
{
[avPlayer pause];
}
- (IBAction)playButton:(id)sender
{
[avPlayer play];
}
#end![enter image description here][1]
The attached image shows the screenshot of the exception
! [1]: http://i.stack.imgur.com/WsxtI.png

Answer 1

AVPlayer has no property called "duration".
"duration" is the property of AVPlayerItem.
And both duration and currentTime are of "CMTime" dataType
We have to get the value of CMTime then update the progress.
-(void) updateMyProgress
{
AVPlayerItem *currentItem = avPlayer.currentItem;
CMTime duration = currentItem.duration; //total time
CMTime currentTime = currentItem.currentTime; //playing time
CGFloat progress = currentTime.value/duration.value;
self.myProgressView.progress = progress;
}