xCode - How to stop one action when another occurs

I have an app that开发者_高级运维 speaks words. However, when word B is pressed, I want to stop word A. Is there a way to do that? This is my code for speaking the words:

-(IBAction)sayIt:(id)sender
{
//NSLog(@"%s", __FUNCTION__);
CFBundleRef mainBundle = CFBundleGetMainBundle();
FlashCardsAppDelegate *mainDelegate = (FlashCardsAppDelegate *)[[UIApplication sharedApplication] delegate];
CFURLRef soundFileURLRef;
soundFileURLRef= CFBundleCopyResourceURL (mainBundle, (CFStringRef)[mainDelegate soundFile], CFSTR("caf"), NULL);   
UInt32 soundID;
AudioServicesCreateSystemSoundID(soundFileURLRef, &soundID);
AudioServicesPlaySystemSound(soundID);
}   

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you can use AVAudioPlayer as a class member, call player.stop and player.play to stop and start audio. if you need to change the sound after stopping the player use InitWithData

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Looking at the docs, it does not look like you can stop it playing the alert until its complete.

But you can use a callback to tell when it has finished playing to avoid playing two sounds. Look at:

AudioServicesAddSystemSoundCompletion

Discussion Because a system sound may play for several seconds, you might want to know when it has finished playing. For example, you may want to wait until a system sound has finished playing before you play another sound.

and

AudioServicesSystemSoundCompletionProc

Discussion Because a system sound may play for up to 30 seconds, the AudioServicesPlaySystemSound function executes asynchronously (that is, it returns immediately). This callback gets invoked when a specified system sound has finished playing. You can use this callback, for example, to help you avoid playing a second sound while a first sound is still playing.