How do you get the directory parameter of pathsForResourcesOfType:inDirectory:?

In my Resources group in XCode I have a subgroup called "AUDIO", and a subgroup of that called "words_audio". I have a bunch of sound files I'm trying to get the paths of. I tried

NSArray *pathsForWordAudio = [NSBundle pathsForResourcesOfType:@"mp3" inDirectory:@"words_audio"];

as well as a few other string parameters, but none of them work. The hierarchy setup of the folders in the directory is 开发者_如何学JAVAthe same as the setup of the group in XCode.

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Basically, when you create a group in XCode - no corresponding folder is created. Moreover, result app bundle for iOS contains no folders at all (except system-dependent like "_CodeSignature" and localizations - "*.lproj"). So pass nil as directory parameter.

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NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];

Code lifted from this SO thread.