EXC_BAD_ACCESS thrown when adding objects to NSMutableArray

Question

I am getting an EXC_BAD_ACCESS error when attempting to add objects to an array. I understand that this could mean I am pointing to something that doesn't exist in memory, or that the objects contain a nil value.

Code:

- (void)fadeInPlayer:(AVAudioPlayer *)player withMaxVolume:(float)maxVolume {

NSLog(@"player: %@", player);
NSLog(@"maxVolume: %f", maxVolume);

NSMutableArray *playerAndVolume = [NSMutableArray arrayWithObjects: player, maxVolume, nil];

if (player.volume <= maxVolume) {
    player.volume = player.volume + 0.1;
    NSLog(@"%@ Fading In", player);
    NSLog(@"Volume %f", player.volume);
    [self performSelector:@selector(fadeInPlayer:withMaxVolume:) withObject:playerAndVolume afterDelay:0.5];
    //playerAndVolume array used here because performSelector can only accept one argument with a delay and I am using two...
    }

}

The strange thing is that when I print the objects I am trying to add to the console (shown as NSLogs above), they return data:

player: <AVAudioPlayer: 0x913f030>
maxVolume: 0.900000

The app crashes immediately after the NSLogs. The rest of the code works fine without the array, but I need to use it to call performselector:withObject:AfterDelay on the method.

So there must be a problem with how I am initialising the array, or maybe the object types, but I can't figure it out.

Any help appreciated.

NJones · Accepted Answer · 2012-12-31 02:10:08Z

4

You can't add a float to an NSArray. You'll have to wrap it in an NSNumber.

But

The real problem is that the first argument passed in is the NSArray you created, the second parameter passed into your function is the NSTimer that backs the performSelector:afterDelay:... methods. It doesn't spread out the objects in your array, it just passes the array as the first argument. If you are insistent upon remaining with this API design then you need to test the class of the first argument to see if it is an NSArray or an AVAudioPlayer. You could implement this function like this:

-(void)fadeInPlayer:(AVAudioPlayer *)player withMaxVolume:(NSNumber *)maxVolume {
    if ([player isKindOfClass:[NSArray class]]){
        // This is a redundant self call, and the player and max volume are in the array.
        // So let's unpack them.
        NSArray *context = (NSArray *)player;
        player = [context objectAtIndex:0];
        maxVolume = [context objectAtIndex:1];
    } 

    NSLog(@"fading in player:%@ at volume:%f to volume:%f",player,player.volume,maxVolume.floatValue);

    if (maxVolume.floatValue == player.volume || maxVolume.floatValue > 1.0) return;

    float newVolume =  player.volume + 0.1;
    if (newVolume > 1.0) newVolume = 1.0;
    player.volume = newVolume;

    if (newVolume < maxVolume.floatValue){
        NSArray *playerAndVolume = [NSArray arrayWithObjects: player, maxVolume, nil];
        [self performSelector:@selector(fadeInPlayer:withMaxVolume:) withObject:playerAndVolume afterDelay:0.5];
    }
}

You would use this, wrapping the float in an NSNumber, like so:

[self fadeInPlayer:player withMaxVolume:[NSNumber numberWithFloat:1.0]];

Please note, this would be considered a very odd function, but this code does run.

edited Dec 31, 2012 at 2:10

answered Dec 31, 2012 at 1:17

NJones

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2 Comments

Michael Mior Over a year ago

Specifically, you need to use [NSNumber numberWithFloat:maxVolume].

MightyMeta Over a year ago

Great, thanks on both counts, was able to identify the problems and fix them. Cheers!

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