opc - Eclipse milo - OPCUA - What is the best practice to inform server (value/node) changes to the client to trigger a refresh?

Question

I am getting started with OPCUA and eclipse milo and I am trying to understand how to best inform the client that a value or node has changed in the server.

So far my guess is that I need to trigger an event in the node that has changed, and then the client should monitor/subscribe to events in such node. Am I right on this?

If my understanding is correct, which event is most appropriated to trigger for this purpose?

I am using a free UI OPCUA client to test my server changes, and I need to refresh manually to observe my changes. I was expecting that by triggering the correct (OPCUA standard) event I would indicate the client to refresh automatically, is this possible?

Thanks!

question from:https://stackoverflow.com/questions/65904518/eclipse-milo-opcua-what-is-the-best-practice-to-inform-server-value-node-c

Answer 1

You don't need Events to notify a client of an attribute change - that's the entire point of Subscriptions and MonitoredItems.

The client creates a MonitoredItem for the Value attribute (or any other attribute) and the server will report changes when that attribute changes.

As far as what you need to do as a user of the Milo Server SDK - see the ExampleNamespace. Your namespace implements the onDataItemCreated and other related methods to be notified that a client has created a MonitoredItem and you should start sampling values for it.