NSSet <NSString> SelectableLayersFromSources(string [] layersId) { if (layersId == null) { return(null); } NSMutableSet <NSString> output = new NSMutableSet <NSString>(); foreach (string layerId in layersId) { var acceptedId = layerId.Replace("_", "-"); output.Add((NSString)acceptedId); output.Add((NSString)(acceptedId + " (1)")); } return(output.Copy() as NSSet <NSString>); }