新增監聽事件：

    [AVAudioSession sharedInstance];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(audioRouteChangeListenerCallback:)
                                                 name:AVAudioSessionRouteChangeNotification
                                               object:nil];
 

- (void)audioRouteChangeListenerCallback:(NSNotification*)notification
{
    NSDictionary *interuptionDict = notification.userInfo;
    
    NSInteger routeChangeReason = [[interuptionDict valueForKey:AVAudioSessionRouteChangeReasonKey] integerValue];
    
    switch (routeChangeReason) {
            
        case AVAudioSessionRouteChangeReasonNewDeviceAvailable:
            NSLog(@"AVAudioSessionRouteChangeReasonNewDeviceAvailable");
            NSLog(@"Headphone/Line plugged in");
            break;
            
        case AVAudioSessionRouteChangeReasonOldDeviceUnavailable:
            NSLog(@"AVAudioSessionRouteChangeReasonOldDeviceUnavailable");
            NSLog(@"Headphone/Line was pulled. Stopping player....");
            break;
            
        case AVAudioSessionRouteChangeReasonCategoryChange:
            // called at start - also when other audio wants to play
            NSLog(@"AVAudioSessionRouteChangeReasonCategoryChange");
            break;
    }
}