多次按下按钮时声音重叠

当我按下一个按钮，然后按下另一个按钮时，声音会重叠。我该如何解决这个问题，以便在按下另一个声音时第一个声音停止？

 - (void)playOnce:(NSString *)aSound {

NSString *path = [[NSBundle mainBundle] pathForResource:aSound ofType:@"caf"];
AVAudioPlayer* theAudio = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL fileURLWithPath:path] error:NULL];
[theAudio setDelegate: self];
[theAudio setNumberOfLoops:0];
[theAudio setVolume:1.0];
[theAudio play];    
 }

- (void)playLooped:(NSString *)aSound {

NSString *path = [[NSBundle mainBundle] pathForResource:aSound ofType:@"caf"];
AVAudioPlayer* theAudio = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL fileURLWithPath:path] error:NULL];
[theAudio setDelegate: self];
// loop indefinitely
[theAudio setNumberOfLoops:-1];
[theAudio setVolume:1.0];
[theAudio play];
[theAudio release];


    }

在 viewController 的标头中声明您的 AVAudioPlayer （不要在每次播放声音时分配一个新的）。这样您将拥有一个可以在 StopAudio 方法中使用的指针。

@interface myViewController : UIViewController <AVAudioPlayerDelegate> { 
    AVAudioPlayer *theAudio;
}
@property (nonatomic, retain) AVAudioPlayer *theAudio;
@end


@implementation myViewController
@synthesize theAudio;
- (void)dealloc {
    [theAudio release];
}
@end



- (void)playOnce:(NSString *)aSound {
    NSString *path = [[NSBundle mainBundle] pathForResource:aSound ofType:@"caf"];
    if(!theAudio){
        theAudio = [[AVAudioPlayer alloc] initWithContentsOfURL: [NSURL fileURLWithPath:path] error:NULL];
    }
    [theAudio setDelegate: self];
    [theAudio setNumberOfLoops:0];
    [theAudio setVolume:1.0];
    [theAudio play];
}

- (void)playLooped:(NSString *)aSound {
    NSString *path = [[NSBundle mainBundle] pathForResource:aSound ofType:@"caf"];
    if(!theAudio){
        theAudio = [[AVAudioPlayer alloc] initWithContentsOfURL: [NSURL fileURLWithPath:path] error:NULL];
    }
    [theAudio setDelegate: self];
    // loop indefinitely
    [theAudio setNumberOfLoops:-1];
    [theAudio setVolume:1.0];
    [theAudio play];
}

- (void)stopAudio {
    [theAudio stop];
    [theAudio setCurrentTime:0];
}

还请务必阅读苹果文档 http://developer.apple.com/library/ios/#documentation/AVFoundation/Reference/AVAudioPlayerClassReference/Reference/Reference.html