What is the difference between setValueConsumer and setEventConsumer

[eclipse]

What is the difference between setValueConsumer and setEventConsumer

[kevinherron]

Events are a special kind of monitored item; the result of subscribing to the Event Notifier attribute of an ObjectNode in which the value of the attribute is non-zero. When you subscribe to events you provide a filter which can narrow down not only which types of events you receive but which fields of that event type your interested in. The Variant[] your event consumer expects will correspond to those fields.

The server doesn't support events yet, so there's no example test case to explain it better, but this gist I put together a while back on how to subscribe to events in the client may clarify: https://gist.github.com/kevinherron/0143b38cc93e19266156

[kevinherron]

Need better javadoc on setEventConsumer methods.

[tosuns]

I have a question regarding the QualifiedName in your example. Is the QualifiedName relative to the readValueId or is it an absolute ?

Another question pops up: Do I understand it correctly that every node can be defined as an Event supplier/notifier? As far as I can see, there is an attribute identifier EventNotifier, which indicates that is the case !?

[kevinherron]

The QualifiedName is determined by which event "fields" you're interested in. In the address space, all of the fields of an event will be property nodes of the event object.

All ObjectNodes have an EventNotifier attribute, but they can only be subscribed to for events if the attribute is set to 1. It's typical for a server to use the Server object as its event notifier, but there's nothing requiring it.

OPC-UA specification part 3, 4, and 5 would all help clarify this bit. Unfortunately OPC-UA is so complex that it's probably not possible to understand it without the aid of the specifications.