应用程序已在运行时静音本地通知声音

I am working on an alarm application. When the app is in the background a local notification informs the user that an alarm is ringing and playing a sound. But when the app is already in foreground I do not want the notification sound to play, but a custom sound. I cannot find how to mute the notification sound and as a result both sounds play simultaneously. Any ideas?I am working on an alarm application. When the