public virtual NSString AddFileWrapper(NSFileWrapper doc) { NSString key; GSFileWrapperDirectoryTypeCheck(); key = doc.PreferredFilename(); if (key == null || key.IsEqualToString("")) { NSException.Raise("NSInvalidArgumentException", "Adding file wrapper with no preferred filename."); return null; } if (((NSDictionary)_wrapperData).ObjectForKey(key) != null) { // FIXME - handle duplicate names } ((NSDictionary)_wrapperData).SetObjectForKey(doc, key); return key; }