Question

I need to create a new NSNumber or integer property called primaryKey to be included with all AVAudioPlayer objects that I create so that I can read the value of that property within the audioPlayerDidFinishPlaying callback and know exactly which database record was played.

The reason I need to do this is: I can’t use the player URL property to determine which database record it was since the same sound file can be used multiple times within the playlist.

How can I add a new property to an existing iOS class like this?

---

Example:

AVAudioPlayer *newAudio = [[AVAudioPlayer alloc] initWithContentsOfURL:soundFileURL error:nil];  

self.theAudio = newAudio; // automatically retain audio and dealloc old file if new file is loaded
if (theAudio != nil) [audioPlayers addObject:theAudio];

[newAudio release];

[theAudio setDelegate: theDelegate];
[theAudio setNumberOfLoops: 0];
[theAudio setVolume: callVolume];

// This is the new property that I want to add
[theAudio setPrimaryKey: thePrimaryKey];

[theAudio play];

Then I’d retrieve it in the callback like this:

- (void) audioPlayerDidFinishPlaying:(AVAudioPlayer *)player successfully:(BOOL)flag 
{    
   NSNumber *finishedSound = [NSNumber numberWithInt:[player primaryKey]];

   // Do something with this information now...
}

Answer 1

You can create a subclass and add your property just like you would when subclassing anything.

Interface

@interface MyAudioPlayer : AVAudioPlayer

@property (nonatomic) int primaryKey;

@end

Implementation

@implementation MyAudioPlayer

@synthesize primaryKey = _primaryKey;

@end

Creating

MyAudioPlayer *player = [[MyAudioPlayer alloc] initWithContentsOfURL:soundFileURL error:nil];
player.primaryKey = thePrimaryKey;
...

Delegate

- (void)audioPlayerDidFinishPlaying:(AVAudioPlayer *)player successfully:(BOOL)flag {
    if ([player isKindOfClass:[MyAudioPlayer class]]) {
        MyAudioPlayer *myPlayer = (MyAudioPlayer *)player;
        NSNumber *primaryKeyObject = [NSNumber numberWithInt:myPlayer.primaryKey];
        ...
    }
}