AudioToolbox iPad problem

I am implementing AudioToolbox framework into my ipad app to try to play a sound effect. Here is my code: I declared a SystemSoundID called explode

NSURL *explodeURL = [NSURL fileURLWithPath:[[NSBundle mainBundle]  
                      pathForResource:@"Explosion" ofType:@"wav"]];
AudioServicesCreateSystemSoundID((__bridge CFURLRef) explodeURL, explode);    
[self performSelector:@selector(playsfx) withObject:nil afterDelay:2.0];

-(void)playsfx {
     AudioServicesPlaySystemSoundID(explode)
}

But for some reason the sou开发者_如何学Cnd never plays.

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try passing the address of explode

AudioServicesCreateSystemSoundID((CFURLRef)explodeURL, &explode);