QOpcUaNode Class

QOpcUaNode *rootNode; // Created before, see QOpcUaClient documentation.
// Connect to the attributeRead signal. Compatible slots of QObjects can be used instead of a lambda.
QObject::connect(rootNode, &QOpcUaNode::attributeRead, [rootNode, client](QOpcUa::NodeAttributes attr) {
    qDebug() << "Signal for attributes:" << attr;
    if (rootNode->attributeError(QOpcUa::NodeAttribute::BrowseName) != QOpcUa::UaStatusCode::Good) {
        qDebug() << "Failed to read attribute:" << rootNode->attributeError(QOpcUa::NodeAttribute::BrowseName);
        client->disconnectFromEndpoint();
    }
    qDebug() << "Browse name:" << rootNode->attribute(QOpcUa::NodeAttribute::BrowseName).value<QOpcUaQualifiedName>().name();
});
rootNode->readAttributes(QOpcUa::NodeAttribute::BrowseName); // Start a read operation for the node's BrowseName attribute.

Member Function Documentation

[signal] void QOpcUaNode::attributeRead(QOpcUa::NodeAttributes attributes)

This signal is emitted after a readAttributes() or readAttributeRange() operation has finished. The receiver has to check the status code for the attributes contained in attributes.

[signal] void QOpcUaNode::attributeUpdated(QOpcUa::NodeAttribute attr, QVariant value)

This signal is emitted after the value in the attribute cache has been updated by a data change notification from the server, a read or a write operation. value contains the new value for the node attribute attr.

See also attribute(), attributeError(), serverTimestamp(), and sourceTimestamp().

[signal] void QOpcUaNode::attributeWritten(QOpcUa::NodeAttribute attribute, QOpcUa::UaStatusCode statusCode)

This signal is emitted after a writeAttribute(), writeAttributes() or writeAttributeRange() operation has finished.

Before this signal is emitted, the attribute cache is updated in case of a successful write. For writeAttributes() a signal is emitted for each attribute in the write call. statusCode contains the success information for the write operation on attribute.

[signal] void QOpcUaNode::browseFinished(QList<QOpcUaReferenceDescription> children, QOpcUa::UaStatusCode statusCode)

This signal is emitted after a browseChildren() or browse() operation has finished.

children contains information about all nodes which matched the criteria in browseChildren(). statusCode contains the service result of the browse operation. If statusCode is not Good, the passed children vector is empty.

See also QOpcUaReferenceDescription.

[signal] void QOpcUaNode::dataChangeOccurred(QOpcUa::NodeAttribute attr, QVariant value)

This signal is emitted after a data change notification has been received. value contains the new value for the node attribute attr.

See also attribute(), serverTimestamp(), and sourceTimestamp().

[signal] void QOpcUaNode::disableMonitoringFinished(QOpcUa::NodeAttribute attr, QOpcUa::UaStatusCode statusCode)

This signal is emitted after an asynchronous call to disableMonitoring() has finished. statusCode contains the status code generated by the operation. After this signal has been emitted, monitoringStatus returns a default constructed value with status code BadMonitoredItemIdIinvalid for attr.

[signal] void QOpcUaNode::enableMonitoringFinished(QOpcUa::NodeAttribute attr, QOpcUa::UaStatusCode statusCode)

This signal is emitted after an asynchronous call to enableMonitoring() has finished. After this signal has been emitted, monitoringStatus() returns valid information for attr. statusCode contains the status code for the operation.

[signal] void QOpcUaNode::eventOccurred(QVariantList eventFields)

This signal is emitted after a new event has been received.

eventFields contains the values of the event fields in the order specified in the select clause of the event filter.

[signal] void QOpcUaNode::methodCallFinished(QString methodNodeId, QVariant result, QOpcUa::UaStatusCode statusCode)

This signal is emitted after a method call for methodNodeId has finished on the server. statusCode contains the status code from the method call, result contains the output arguments of the method. result is empty if the method has no output arguments or statusCode is not Good. The result variant is either a single value if there is only one output argument or it contains a list of variants in case the called function returned multiple output arguments.

if (result.canConvert<QVariantList>()) {
    // handle list type
} else {
    // handle value type
}

[signal] void QOpcUaNode::monitoringStatusChanged(QOpcUa::NodeAttribute attr, QOpcUaMonitoringParameters::Parameters items, QOpcUa::UaStatusCode statusCode)

This signal is emitted after an asynchronous call to modifyMonitoring() has finished. The node attribute for which the operation was requested is returned in attr. items contains the parameters that have been modified. statusCode contains the result of the modify operation on the server.

[signal] void QOpcUaNode::resolveBrowsePathFinished(QList<QOpcUaBrowsePathTarget> targets, QList<QOpcUaRelativePathElement> path, QOpcUa::UaStatusCode statusCode)

This signal is emitted after a resolveBrowsePath() call has finished.

QOpcUaBrowsePathTarget targets contains the matches, statusCode is the status code of the operation. If statusCode is not Good, targets is empty. The browse path path is the browse path from the request. It can be used to associate results with requests.

[static] QOpcUa::NodeAttributes QOpcUaNode::allBaseAttributes()

Contains all attributes of the OPC UA base node class.

QVariant QOpcUaNode::attribute(QOpcUa::NodeAttribute attribute) const

Returns the value of the attribute given in attribute.

The value is only valid after the attributeRead signal has been emitted. An empty QVariant is returned if there is no cached value for the attribute.

QOpcUa::UaStatusCode QOpcUaNode::attributeError(QOpcUa::NodeAttribute attribute) const

Returns the error code for the attribute given in attribute.

The error code is only valid after the attributeRead or attributeWritten signal has been emitted.

If there is no entry in the attribute cache, BadNoEntryExists is returned.

See also QOpcUa::errorCategory.

bool QOpcUaNode::browse(const QOpcUaBrowseRequest &request)

Starts a browse call from this node.

Returns true if the asynchronous call has been successfully dispatched.

All references matching the criteria specified in request are returned in the browseFinished() signal.

For example, an inverse browse call can be used to find the parent node of a property node:

QOpcUaBrowseRequest request;
request.setBrowseDirection(QOpcUaBrowseRequest::BrowseDirection::Inverse);
request.setReferenceTypeId(QOpcUa::ReferenceTypeId::HasProperty);
propertyNode->browse(request);

bool QOpcUaNode::browseChildren(QOpcUa::ReferenceTypeId referenceType = QOpcUa::ReferenceTypeId::HierarchicalReferences, QOpcUa::NodeClasses nodeClassMask = QOpcUa::NodeClass::Undefined)

Executes a forward browse call starting from the node this method is called on. The browse operation collects information about child nodes connected to the node and delivers the results in the browseFinished() signal.

Returns true if the asynchronous call has been successfully dispatched.

To request only children connected to the node by a certain type of reference, referenceType must be set to that reference type. For example, this can be used to get all properties of a node by passing HasProperty in referenceType. The results can be filtered to contain only nodes with certain node classes by setting them in nodeClassMask.

bool QOpcUaNode::callMethod(const QString &methodNodeId, const QList<QOpcUa::TypedVariant> &args = QList<QOpcUa::TypedVariant>())

Calls the OPC UA method methodNodeId with the parameters given via args. The result is returned in the methodCallFinished signal.

Returns true if the asynchronous call has been successfully dispatched.

QOpcUaClient *QOpcUaNode::client() const

Returns a pointer to the client that has created this node.

bool QOpcUaNode::disableMonitoring(QOpcUa::NodeAttributes attr)

This method disables monitoring for the attributes given in attr.

Returns true if the asynchronous call has been successfully dispatched.

After the call is finished, the disableMonitoringFinished signal is emitted and monitoringStatus returns a default constructed value with status code BadMonitoredItemIdIinvalid for attr.

bool QOpcUaNode::enableMonitoring(QOpcUa::NodeAttributes attr, const QOpcUaMonitoringParameters &settings)

This method creates a monitored item for each of the attributes given in attr. The settings from settings are used in the creation of the monitored items and the subscription.

Returns true if the asynchronous call has been successfully dispatched.

On completion of the call, the enableMonitoringFinished signal is emitted. There are multiple error cases in which a bad status code is generated: A subscription with the subscription id specified in settings does not exist, the node does not exist on the server, the node does not have the requested attribute or the maximum number of monitored items for the server is reached.

The same method is used to enable event monitoring. Events are special objects in the OPC UA address space which contain information about an event that has occurred. If an event is triggered on the server, an event monitored item collects selected values of node attributes of the event object and its child nodes. Every node that has an event source can be monitored for events. To monitor a node for events, the attribute EventNotifier must be monitored using an EventFilter which contains the event fields the user needs and optionally a where clause which is used to filter events by criteria (for more details, see QOpcUaMonitoringParameters::EventFilter).

[static] QOpcUa::NodeAttributes QOpcUaNode::mandatoryBaseAttributes()

Contains all mandatory attributes of the OPC UA base node class.

bool QOpcUaNode::modifyDataChangeFilter(QOpcUa::NodeAttribute attr, const QOpcUaMonitoringParameters::DataChangeFilter &filter)

Modifies an existing data change monitoring to use filter as data change filter.

Returns true if the filter modification request has been successfully dispatched to the backend.

monitoringStatusChanged for attr is emitted after the operation has finished.

bool QOpcUaNode::modifyEventFilter(const QOpcUaMonitoringParameters::EventFilter &eventFilter)

Modifies an existing event monitoring to use eventFilter as event filter.

Returns true if the filter modification request has been successfully dispatched to the backend.

monitoringStatusChanged for EventNotifier is emitted after the operation has finished.

bool QOpcUaNode::modifyMonitoring(QOpcUa::NodeAttribute attr, QOpcUaMonitoringParameters::Parameter item, const QVariant &value)

This method modifies settings of the monitored item or the subscription. The parameter item of the monitored item or subscription associated with attr is attempted to set to value.

Returns true if the asynchronous call has been successfully dispatched.

After the call has finished, the monitoringStatusChanged signal is emitted. This signal contains the modified parameters and the status code. A bad status code is generated if there is no monitored item associated with the requested attribute, modifying the requested parameter is not implemented or if the server has rejected the requested value.

QOpcUaMonitoringParameters QOpcUaNode::monitoringStatus(QOpcUa::NodeAttribute attr)

Returns the monitoring parameters associated with the attribute attr. This can be used to check the success of enableMonitoring() or if parameters have been revised. The returned values are only valid after enableMonitoringFinished or monitoringStatusChanged have been emitted for attr. If the status is queried before a signal has been emitted, QOpcUaMonitoringParameters::statusCode() returns BadNoEntryExists.

QString QOpcUaNode::nodeId() const

Returns the ID of the OPC UA node.

bool QOpcUaNode::readAttributeRange(QOpcUa::NodeAttribute attribute, const QString &indexRange)

Starts an asynchronous read operation for the node attribute attribute. indexRange is a string which can be used to select a part of an array. It is defined in OPC-UA part 4, 7.22. The first element in an array is 0, "1" returns the second element, "0:9" returns the first 10 elements, "0,1" returns the second element of the first row in a two-dimensional array.

Returns true if the asynchronous call has been successfully dispatched.

Attribute values only contain valid information after the attributeRead signal has been emitted.

bool QOpcUaNode::readAttributes(QOpcUa::NodeAttributes attributes = mandatoryBaseAttributes())

Starts an asynchronous read operation for the node attributes in attributes.

Returns true if the asynchronous call has been successfully dispatched.

Attribute values only contain valid information after the attributeRead signal has been emitted.

[since 6.3] QOpcUaHistoryReadResponse *QOpcUaNode::readHistoryRaw(const QDateTime &startTime, const QDateTime &endTime, quint32 numValues, bool returnBounds)

Starts a read history request for this node. This is the Qt OPC UA representation for the OPC UA ReadHistory service for reading raw historical data defined in OPC-UA part 4, 5.10.3. It reads the history based on the parementers, startTime, endTime, numValues, and returnBounds.

Returns a QOpcUaHistoryReadResponse which contains the state of the request if the asynchronous request has been successfully dispatched. The results are returned in the QOpcUaHistoryReadResponse::readHistoryDataFinished(const QList<QOpcUaHistoryData> &results, QOpcUa::UaStatusCode serviceResult) signal.

In the following example, the historic data from the last two days of a node are requested and printed. The result is limited to ten values per node.

QOpcUaHistoryReadResponse *response = node->readHistoryRaw(QDateTime::currentDateTime(),
                                                           QDateTime::currentDateTime().addDays(-2),
                                                           10,
                                                           true);
if (response) {
    QObject::connect(response123, &QOpcUaHistoryReadResponse::readHistoryDataFinished,
                     [] (QList<QOpcUaHistoryData> results, QOpcUa::UaStatusCode serviceResult) {
        if (serviceResult != QOpcUa::UaStatusCode::Good) {
            qWarning() << "Fetching historical data failed with:" << serviceResult;
        } else {
            for (const auto& result : results) {
                qInfo() << "NodeId:" << result.nodeId();
                for (const auto &dataValue : result.result())
                    qInfo() << "Value:" << dataValue.value();
            }
        }
    });
}

This function was introduced in Qt 6.3.

bool QOpcUaNode::readValueAttribute()

Starts an asynchronous read operation for the node's Value attribute.

Returns true if the asynchronous call has been successfully dispatched.

See also readAttributes().

bool QOpcUaNode::resolveBrowsePath(const QList<QOpcUaRelativePathElement> &path)

Resolves the browse path path to one or more node ids starting from this node using the TranslateBrowsePathsToNodeIds service specified in OPC-UA part 4, 5.8.4.

Returns true if the asynchronous call has been successfully dispatched.

TranslateBrowsePathsToNodeIds is mainly used to program against type definitions instead of a concrete set of nodes in the OPC UA address space. For example, a type definition for a machine model could consist of a starting node with browse name "Machine" which has a component with browse name "Fan". Fan has a component with browse name "RPM" which is a Variable node holding the current RPM value of the fan. There are multiple machines of that type and each of these machines is mapped into the OPC UA address space as an object of the machine type. For each of these machine objects, the path from the machine node to the "RPM" node is the same. If a client wants to read the current RPM value, it needs to call resolveBrowsePath() with the machine node as starting node and the browse path from the machine to the "RPM" node:

QScopedPointer<QOpcUaNode> node(opcuaClient->node("ns=1;s=machine1"));

QList<QOpcUaRelativePathElement> path;
path.append(QOpcUaRelativePathElement(QOpcUaQualifiedName(1, "Fan"), QOpcUa::ReferenceTypeId::HasComponent));
path.append(QOpcUaRelativePathElement(QOpcUaQualifiedName(1, "RPM"), QOpcUa::ReferenceTypeId::HasComponent));
node->resolveBrowsePath(path);

The result returned in resolveBrowsePathFinished() contains the node id of the "RPM" node which can be used to access the node's attributes:

if (!results.size()) {
    qWarning() << "Browse path resolution failed";
    return;
}

if (results.at(0).isFullyResolved()) {
   QOpcUaNode *rpmNode = client->node(results.at(0).targetId());
   if (!rpmNode) {
       qWarning() << "Failed to create node";
       return;
   }
   // Connect slots, call methods
} else {
    qWarning() << "Browse path could not be fully resolved, the target node is on another server";
    return;
}

QDateTime QOpcUaNode::serverTimestamp(QOpcUa::NodeAttribute attribute) const

Returns the server timestamp from the last read or data change of attribute. Before at least one attributeRead or dataChangeOccurred signal has been emitted, a null datetime is returned.

QDateTime QOpcUaNode::sourceTimestamp(QOpcUa::NodeAttribute attribute) const

Returns the source timestamp from the last read or data change of attribute. Before at least one attributeRead or dataChangeOccurred signal has been emitted, a null datetime is returned.

QVariant QOpcUaNode::valueAttribute() const

Returns the value of the node's Value attribute.

The returned value is only valid after the Value attribute has been successfully read or written or after a data change from a monitoring has updated the attribute cache. This is indicated by a attributeRead() or attributeWritten() signal with status code Good or a dataChangeOccurred() signal for the Value attribute.

If there is no value in the attribute cache, an invalid QVariant is returned.

See also readValueAttribute(), writeValueAttribute(), and valueAttributeError().

QOpcUa::UaStatusCode QOpcUaNode::valueAttributeError() const

Returns the error code for the node's Value attribute. The status code Good indicates a valid return value for valueAttribute(). If there is no entry in the attribute cache, BadNoEntryExists is returned.

bool QOpcUaNode::writeAttribute(QOpcUa::NodeAttribute attribute, const QVariant &value, QOpcUa::Types type = QOpcUa::Types::Undefined)

Writes value to the attribute given in attribute using the type information from type. Returns true if the asynchronous call has been successfully dispatched.

If the type parameter is omitted, the backend tries to find the correct type. The following default types are assumed:

bool QOpcUaNode::writeAttributeRange(QOpcUa::NodeAttribute attribute, const QVariant &value, const QString &indexRange, QOpcUa::Types type = QOpcUa::Types::Undefined)

Writes value to the attribute given in attribute using the type information from type. For indexRange, see readAttributeRange().

Returns true if the asynchronous call has been successfully dispatched.

bool QOpcUaNode::writeAttributes(const QOpcUaNode::AttributeMap &toWrite, QOpcUa::Types valueAttributeType = QOpcUa::Types::Undefined)

Executes a write operation for the attributes and values specified in toWrite.

Returns true if the asynchronous call has been successfully dispatched.

The valueAttributeType parameter can be used to supply type information for the value attribute. All other attributes have known types.

See also writeAttribute().

bool QOpcUaNode::writeValueAttribute(const QVariant &value, QOpcUa::Types type = QOpcUa::Types::Undefined)

Writes value to the node's Value attribute using the type information from type.

Returns true if the asynchronous call has been successfully dispatched.

See also writeAttribute().