// Registers a |handler| for the event with |eventName|. Supported event names: error, result. See corresponding // handler types above. public FunctionCall On(string eventName, Delegate handler) { ValidateHandler(eventName, handler); if (eventName == "result") { OnResult.Add(handler); } else if (eventName == "exception") { OnException.Add(handler); } else if (eventName == "error") { OnError += (CallErrorCallback)handler; } return(this); }