An event can only serve for delivering data from the source to the target. When you map an event, the event handler has to accept two arguments. The first argument is the sender – the target object itself. The second argument contains the mapped data, and is of type TargetDataEventArgs<TData> (if the target type is not known) or TargetDataEventArgs<TData,TTarget> (for target of type TTarget).

TData is the type of data, as given by the mapping (see Mapping Kinds for details on types for different kinds of mappings).