AVAudioPlayer Help: Playing multiple sounds simultaneously, stopping them all at once, and working around Automatic Reference Counting

Question

I am trying to create buttons that play single sound files and one button that stops all of the sounds that are currently playing. If the user clicks multiple buttons or the same button in a short amount of time, the app should be playing all of the sounds simultaneously. I have accomplished this without much difficulty using the System Sound Services of iOS. However, the System Sound Services play the sounds through the volume that the iPhone's ringer is set to. I am now trying to use the AVAudioPlayer so that users can play the sounds through the media volume. Here is the code that I am currently (yet unsuccessfully) using the play the sounds:

-(IBAction)playSound:(id)sender
{
   AVAudioPlayer *audioPlayer;
   NSString *soundFile = [[NSBundle mainBundle] pathForResource:@"Hello" ofType:@"wav"];
   audioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL fileURLWithPath:soundFile] error:nil];
   [audioPlayer prepareToPlay];
   [audioPlayer play];
}

Whenever I run this code in the iPhone Simulator, it does not play the sound but does display a ton of output. When I run this on my iPhone, the sound simply does not play. After doing some research and testing, I found that the audioPlayer variable is being released by Automatic Reference Counting. Also, this code works when the audioPlayer variable is defined as an instance variable and a property in my interface file, but it does not allow me to play multiple sounds at once.

First thing's first: How can I play an infinite number of sounds at once using the AVAudioPlayer and sticking with Automatic Reference Counting? Also: When these sounds are playing, how can I implement a second IBAction method to stop playing all of them?

Solution

First off, put the declaration and alloc/init of audioplayer on the same line. Also, you can only play one sound per AVAudioPlayer BUT you can make as many as you want simultaneously. And then to stop all of the sounds, maybe use a NSMutableArray, add all of the players to it, and then iterate though and [audioplayer stop];

//Add this to the top of your file
NSMutableArray *soundsArray;

//Add this to viewDidLoad
soundsArray = [NSMutableArray new]

//Add this to your stop method
for (AVAudioPlayer *a in soundsArray) [a stop];

//Modified playSound method
-(IBAction)playSound:(id)sender {
     NSString *soundFile = [[NSBundle mainBundle] pathForResource:@"Hello" ofType:@"wav"];
     AVAudioPlayer *audioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL fileURLWithPath:soundFile] error:nil];
     [soundsArray addObject:audioPlayer];
     [audioPlayer prepareToPlay];
     [audioPlayer play];
  }

That should do what you need.

Comments

[lothorp]

It's worth noting that under ARC, you can't just allocate a local instance of AVAudioPlayer and play it. You have to retain it in some way. A strong property worked in my case.

[bgottlob]

Thanks, this works perfectly. Just for future reference, aside from allowing the audio players to be manipulated in the stop method, does putting the audio players in the array prevent Automatic Reference Counting from releasing the audio players' memory before the end of the playSound method?

[Dustin]

It should, but ARC has a habit of working perfectly until it randomly doesn't. I wouldn't worry about it.

[adrian Coye]

In order to avoid leaks you want to set the delegate of audioPlayer and in the following delegate method remove the reference from the array : - (void)audioPlayerDidFinishPlaying:(AVAudioPlayer *)player successfully:(BOOL)flag { [self.soundsArray removeObject:player]; }