To throw an exception from an operation implementation, you simply instantiate the exception, initialize it, and throw it. For example:
Note that, for this example, we have supplied the optional second parameter to the
GenericError constructor. This parameter sets the
InnerException member of
System.Exception and preserves the original cause of the error for later diagnosis.
If you throw an arbitrary C# run-time exception (such as an
InvalidCastException), the Ice run time catches the exception and then returns an
UnknownException to the client.
The server-side Ice run time does not validate user exceptions thrown by an operation implementation to ensure they are compatible with the operation's Slice definition. Rather, Ice returns the user exception to the client, where the client-side run time will validate the exception as usual and raise
UnknownUserException for an unexpected exception type.
If you throw an Ice run-time exception, such as
MemoryLimitException, the client receives an
UnknownLocalException. For that reason, you should never throw Ice run-time exceptions from operation implementations. If you do, all the client will see is an
UnknownLocalException, which does not tell the client anything useful.
Three run-time exceptions are treated specially and not changed to
UnknownLocalException when returned to the client: