How SubscribeForModelChangeEvents is implemented in UaClient

[jack_thomas]

Dear expert,

I am implementing OPC UA Client and I wonder how can I implement Auto-browsing feature in my client.
The Ua Demo Server implementation has dynamic node where in I can observer the node is dynamically update in UaExpert.
I want to implement similar feature in my basic client implementation.
Is it already provided in the example? Please give me the related links.

Thank you,
Jack

[Support Team]

Hallo Jack,

There is no example for the client side.
You have to create a subscription and an EventMonitoredItem for the Server object. You have to select the Changes event field and add a WhereClause to receive only ModelChange events. After you receive the event notification, you can evaluate the value of Changes and rebrowse the node specified by Affected.

[royfyhr]

Hi,

I have tried to figure out how to implement the SelectClause and the WhereClause to fullfill the description provided below. I have managed to set up a EventMonitoredItem for the Server object and receives plenty of events when a new node is added dynamically to the model. Problem is that I have not managed to figure out how to use the SelecClause and the WhereClause to limit the events to GeneralModelChangeEventType events and get hold of the Changes property. Is it possible to get a small example showing how to do this?

Thanks
/Roy

[Support Team]

Hello,

Here is a small example for setting the SelectClause and the WhereClaus:

Code: Select all

            NodeId eventTypeId = ObjectTypeIds.BaseModelChangeEventType;
            EventMonitoredItem monitoredItem = new EventMonitoredItem(ObjectIds.Server);
            monitoredItem.Filter.SelectClauses.Add(new QualifiedName(BrowseNames.Changes));
            monitoredItem.Filter.WhereClauses.Add(
                FilterOperator.OfType,
                new LiteralOperand()
                {
                    Value = new Variant(eventTypeId)
                });