Generating DataChange to client with a minimalistic server

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Jr. Member
Jr. Member
Posts: 1
Joined: 23 Apr 2021, 12:01

Generating DataChange to client with a minimalistic server

Post by seanka »


I am trying to write a small server but I am a bit lost
when it comes to the general architecture so I am not sure
I am doing it in the right way.

So I have a class wrapper where inside I have a member variable
std::unique_ptr<UaApplication> m_application which I initialize
in the ctor.

I add variables to the application like this

Code: Select all

UaNodeId nodeId(itemPath.c_str(), GetNameSpaceIndex());
auto* pVariable = new OpcUa::BaseDataVariableType( 
	GetNameSpaceIndex(), // browse

pVariable->setValueHandling(UaVariable_Value_CacheIsSource); // needed?

if (auto const ret = nodeManagerConfig->addNodeAndReference(sourceNode, pVariable, OpcUaId_HasComponent); 
So an item path would be something like Applications.Application_1.Diagram1.MyVar which
in our case will be the nodeid together with a namespace index.

I seem to be able to read and write to the variables but when writing to a variable
I would like the client to get a datachange but it is not receiving that for some reason.

I write and read to the variables using serverManager->read/write from an update thread
that should simulate values changes so that the client gets datachange calls.

Am I on the right track or am I completely lost? :) I am using the default nodemanager and intenalsession.

How do I enable so that when values are changed by a write that client gets a data change?

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Support Team
Hero Member
Hero Member
Posts: 2670
Joined: 18 Mar 2011, 15:09

Re: Generating DataChange to client with a minimalistic server

Post by Support Team »


We do not completely understand your test setup (especially the serverManager->read/write) but we think you set the wrong value handling.

Simply remove the "pVariable->setValueHandling(UaVariable_Value_CacheIsSource);"
The default setting is handling everything if you update the value with write or pVariable->setValue.
Best regards
Unified Automation Support Team

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