Used by Lightstreamer Kernel to receive the Item Events and any asynchronous severe error notification from the Data Adapter. The listener instance is supplied to the Data Adapter by Lightstreamer Kernel (through the Remote Server) through a SetListener call. The listener can manage multiple kinds of Item Events: IItemEvent objects, IIndexedItemEvent objects and IDictionary objects. The common characteristics of all these kinds of Item Event objects are that: 

- they contain the new values and, in some cases, the current values of the Fields of an Item; the Item name is not directly asked to the object; 

- they provide an enumerator that supplies the names of all the Fields reported in the Item Event; 

- they provide a method for getting the value of a Field by name; the value can be expressed either as a String or as a byte array (the special mandatory fields for COMMAND Mode named "key" and "command" must be encoded as String). 

When an Item Event instance has been sent to the listener, it is totally owned by Lightstreamer and it must not be furtherly changed by the Data Adapter. The Remote Server may also hold the object for some time after the listener call has returned. When Item Events are implemented as wrappers of the data objects received from the external feed (like JMS Messages), this has to be considered. 

public: __interface IItemEventListener;

public interface IItemEventListener;

Public Interface IItemEventListener