I need to define symbols based on selective values across multiple attributes (e.g. attribute A = "foo" OR attribute B = "bar") and I can't figure out how to achieve that using AGSUniqueValueRenderer in the iOS SDK. Is there a way?
I also didn't have much luck subclassing AGSRenderer and defining my own symbolForFeature logic.
So it looks like valueExpression on a UVR should work, there just isn't an API in Runtime to manipulate it.
One thing you could try is to define a UVR with a valueExpression in the JS API and use toJson() on it to get back JSON, translate that JSON to a NSDictionary, then provide that dictionary to the Runtime's AGSUniqueValueRenderer.fromJSON:error:() method.
Does that help? Let me know how that goes.