UA OPC Server data types

Question

For the life of me I can't find out the answer to what I thought would have been a simple question - how to find the data typeof an OPC Node.

I'm writing a UA OPC library which involves creating a subscription and the monitoring/updating of tags within this subscription.

The request to write to a tag comes from an external application and consists of Subscription and tag ID together with an object value. The issue is that this object is invariably a string (don't ask), which needs to be converted to an appropriate data type for the tag. So, I need to find out what data type is associated with the tag. At the moment, the writing fails with a type mismatch exception.

Here's my update code:

//
    // Extension methods
    public bool Write<T>(long groupID, long tagID, T item)
    {
        var sub = FindSubscription(groupID);
        try
        {
            if (sub != null)
            {
                var node = sub.MonitoredItems.FirstOrDefault(m => (long)m.Handle == tagID);

                if (node != null)
                {
                    bool result = false;
                    var nodesToWrite = BuildWriteValueCollection(node.DisplayName, Attributes.Value, item);

                    StatusCodeCollection results;
                    DiagnosticInfoCollection diag;
                    try
                    {
                        _session.Write(
                        requestHeader: null,
                        nodesToWrite: nodesToWrite,
                        results: out results,
                        diagnosticInfos: out diag);


                        result = CheckReturnValue(results[0]);

                    }
                    catch (Exception ex)
                    {

                    }
                }
            }
        }
        catch  (Exception ex)
        {
            LogMessage(String.Format("Write GroupID {0}, Tag  {1}, Value {2}", groupID, tagID, item.ToString()), ex);
        }

        return false;
    }

I've searched for ages to find out how to determine the data type of the node, but without success. So, for a MonitoredItem, how would one go about finding the data type so that I can convert the string to a compatible type?

Thanks

Steve

Answer 1

Read the DataType attribute of the VariableNode in question.