QOpcUaClient Class

QOpcUaProvider provider;
if (provider.availableBackends().isEmpty())
    return;
QOpcUaClient *client = provider.createClient(provider.availableBackends()[0]);
if (!client)
    return;
// Connect to the stateChanged signal. Compatible slots of QObjects can be used instead of a lambda.
QObject::connect(client, &QOpcUaClient::stateChanged, [client](QOpcUaClient::ClientState state) {
    qDebug() << "Client state changed:" << state;
    if (state == QOpcUaClient::ClientState::Connected) {
        QOpcUaNode *node = client->node("ns=0;i=84");
        if (node)
            qDebug() << "A node object has been created";
    }
});

QObject::connect(client, &QOpcUaClient::endpointsRequestFinished,
                 [client](QList<QOpcUaEndpointDescription> endpoints) {
    qDebug() << "Endpoints returned:" << endpoints.count();
    if (endpoints.size())
        client->connectToEndpoint(endpoints.first()); // Connect to the first endpoint in the list
});

client->requestEndpoints(QUrl("opc.tcp://127.0.0.1:4840")); // Request a list of endpoints from the server

Member Function Documentation

[signal] void QOpcUaClient::addNodeFinished(QOpcUaExpandedNodeId requestedNodeId, QString assignedNodeId, QOpcUa::UaStatusCode statusCode)

This signal is emitted after an addNode() operation has finished. requestedNodeId is the requested node id from the addNode() call, assignedNodeId is the node id the server has assigned to the new node. statusCode contains the result of the operation. If the result is Bad, assignedNodeId is empty and no node has been added to the server's address space.

[signal] void QOpcUaClient::addReferenceFinished(QString sourceNodeId, QString referenceTypeId, QOpcUaExpandedNodeId targetNodeId, bool isForwardReference, QOpcUa::UaStatusCode statusCode)

This signal is emitted after an addReference() operation has finished. sourceNodeId, referenceTypeId, targetNodeId and isForwardReference are the values from the addReference() call. statusCode contains the result of the operation.

[signal, since QtOpcUa 5.13] void QOpcUaClient::connectError(QOpcUaErrorState *errorState)

This signal is emitted when an error happened during connection establishment. The parameter errorState contains information about the error.

In case of client side errors, these can be ignored by calling QOpcUaErrorState::setIgnoreError on the object.

During execution of a slot connected to this signal the backend is stopped and waits for all slots to return. This allows to pop up a user dialog to ask the enduser for example if to trust an unknown certificate before the backend continues.

This function was introduced in QtOpcUa 5.13.

[signal] void QOpcUaClient::connected()

This signal is emitted when a connection has been established.

[signal] void QOpcUaClient::deleteNodeFinished(QString nodeId, QOpcUa::UaStatusCode statusCode)

This signal is emitted after a deleteNode() operation has finished. nodeId is the node id from the deleteNode() call. statusCode contains the result of the operation.

[signal] void QOpcUaClient::deleteReferenceFinished(QString sourceNodeId, QString referenceTypeId, QOpcUaExpandedNodeId targetNodeId, bool isForwardReference, QOpcUa::UaStatusCode statusCode)

This signal is emitted after a deleteReference() operation has finished. sourceNodeId, referenceTypeId, targetNodeId and isForwardReference are the values from the deleteReference() call. statusCode contains the result of the operation.

[signal] void QOpcUaClient::disconnected()

This signal is emitted when a connection has been closed following to a close request.

[signal] void QOpcUaClient::endpointsRequestFinished(QList<QOpcUaEndpointDescription> endpoints, QOpcUa::UaStatusCode statusCode, QUrl requestUrl)

This signal is emitted after a requestEndpoints() operation has finished. statusCode contains the result of the operation. If the result is Good, endpoints contains the descriptions of all endpoints that are available on the server. requestUrl contains the URL that was used in the requestEndpoints() call.

[signal] void QOpcUaClient::findServersFinished(QList<QOpcUaApplicationDescription> servers, QOpcUa::UaStatusCode statusCode, QUrl requestUrl)

This signal is emitted after a findServers() operation has finished. statusCode contains the result of the operation. If the result is Good, servers contains the application descriptions of all servers known to the queried server that matched the filter criteria. requestUrl contains the URL that was used in the findServers() call.

[signal] void QOpcUaClient::namespaceArrayChanged(QStringList namespaces)

This signal is emitted after the namespace array has changed. namespaces contains the content of the server's namespace table. The index of an entry in namespaces corresponds to the namespace index used in the node id.

See also namespaceArrayUpdated() and updateNamespaceArray().

[signal] void QOpcUaClient::namespaceArrayUpdated(QStringList namespaces)

This signal is emitted after an updateNamespaceArray operation has finished. namespaces contains the content of the server's namespace table. The index of an entry in namespaces corresponds to the namespace index used in the node id.

If the namespace array content stays the same after the update this signal is emitted nevertheless.

See also namespaceArrayChanged() and updateNamespaceArray().

[signal, since QtOpcUa 5.13] void QOpcUaClient::passwordForPrivateKeyRequired(QString keyFilePath, QString *password, bool previousTryWasInvalid)

This signal is emitted when a password for an encrypted private key is required. The parameter keyFilePath contains the file path to key which is used. The parameter previousTryWasInvalid is true if a previous try to decrypt the key failed (aka invalid password). The parameter password points to a QString that has to be filled with the actual password for the key. In case the previous try failed it contains the previously used password.

During execution of a slot connected to this signal the backend is stopped and waits for all slots to return. This allows to pop up a user dialog to ask the enduser for the password.

This function was introduced in QtOpcUa 5.13.

[signal] void QOpcUaClient::readNodeAttributesFinished(QList<QOpcUaReadResult> results, QOpcUa::UaStatusCode serviceResult)

This signal is emitted after a readNodeAttributes() operation has finished.

The elements in results have the same order as the elements in the request. For each requested element, there is a value together with timestamps and the status code in results. serviceResult contains the status code from the OPC UA Read service.

See also readNodeAttributes(), QOpcUaReadResult, and QOpcUaReadItem.

[signal] void QOpcUaClient::writeNodeAttributesFinished(QList<QOpcUaWriteResult> results, QOpcUa::UaStatusCode serviceResult)

This signal is emitted after a writeNodeAttributes() operation has finished.

The elements in results have the same order as the elements in the write request. They contain the value, timestamps and status code received from the server as well as the node id, attribute and index range from the write item. This facilitates matching the result with the request.

serviceResult is the status code from the the OPC UA Write service. If serviceResult is not Good, the entries in results also have an invalid status code and must not be used.

See also writeNodeAttributes() and QOpcUaWriteResult.

[virtual] QOpcUaClient::~QOpcUaClient()

Destroys the QOpcUaClient instance.

bool QOpcUaClient::addNode(const QOpcUaAddNodeItem &nodeToAdd)

Adds the node described by nodeToAdd on the server.

Returns true if the asynchronous call has been successfully dispatched.

The success of the operation is returned in the addNodeFinished() signal.

The following example code adds new a Variable node on the server:

QOpcUaNodeCreationAttributes attributes;
attributes.setDisplayName(QOpcUaLocalizedText("en", "My new Variable node"));
attributes.setDescription(QOpcUaLocalizedText("en", "A node which has been added at runtime"));
attributes.setValue(23.0, QOpcUa::Types::Double);
attributes.setDataTypeId(QOpcUa::ns0ID(QOpcUa::NodeIds::Namespace0::Double));
attributes.setValueRank(-2); // Scalar or array
attributes.setAccessLevel(QOpcUa::AccessLevelBit::CurrentRead);
attributes.setUserAccessLevel(QOpcUa::AccessLevelBit::CurrentRead);

QOpcUaAddNodeItem item;
item.setParentNodeId(QOpcUaExpandedNodeId("ns=3;s=TestFolder"));
item.setReferenceTypeId(QOpcUa::nodeIdFromReferenceType(QOpcUa::ReferenceTypeId::Organizes));
item.setRequestedNewNodeId(QOpcUaExpandedNodeId("ns=3;s=MyNewVariableNode"));
item.setBrowseName(QOpcUaQualifiedName(3, "MyNewVariableNode"));
item.setNodeClass(QOpcUa::NodeClass::Variable);
item.setNodeAttributes(attributes);

m_client->addNode(item);

See also deleteNode(), addNodeFinished(), and QOpcUaAddNodeItem.

bool QOpcUaClient::addReference(const QOpcUaAddReferenceItem &referenceToAdd)

Adds the reference described by referenceToAdd to the server.

Returns true if the asynchronous call has been successfully dispatched.

The success of the operation is returned in the addReferenceFinished() signal.

The following example code adds a reference to a node to the "Objects" folder:

QOpcUaAddReferenceItem item;
item.setSourceNodeId(QOpcUa::namespace0Id(QOpcUa::NodeIds::Namespace0::ObjectsFolder));
item.setReferenceTypeId(QOpcUa::nodeIdFromInteger(0, static_cast<quint32>(QOpcUa::ReferenceTypeId::Organizes)));
item.setIsForwardReference(true);
item.setTargetNodeId(QOpcUaExpandedNodeId("ns=3;s=MyNewVariableNode"));
item.setTargetNodeClass(QOpcUa::NodeClass::Variable);

m_client->addReference(item);

See also deleteReference(), addReferenceFinished(), and QOpcUaAddReferenceItem.

[since QtOpcUa 5.13] QOpcUaApplicationIdentity QOpcUaClient::applicationIdentity() const

Returns the application identity of this QOpcUaClient instance.

This function was introduced in QtOpcUa 5.13.

See also setApplicationIdentity().

const QOpcUaAuthenticationInformation &QOpcUaClient::authenticationInformation() const

Returns the current authentication information.

See also setAuthenticationInformation().

QString QOpcUaClient::backend() const

Returns the name of the backend used by this instance of QOpcUaClient, e.g. "open62541".

[invokable, since QtOpcUa 5.13] void QOpcUaClient::connectToEndpoint(const QOpcUaEndpointDescription &endpoint)

Connects to the OPC UA endpoint given in endpoint.

QEndpointDescription endpointDescription;
...
client->connectToEndpoint(endpointDescription);

A list of available endpoints is usually obtained by calling QOpcUaClient::requestEndpoints().

If the endpoint requires username authentication, at least a user name must be set in QOpcUaAuthenticationInformation. Calling this function before setting an authentication information will use the anonymous authentication.

QOpcUaAuthenticationInformation authInfo;
authInfo.setUsernameAuthentication("user", "password");

client->setAuthenticationInformation(authInfo);

Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.

This function was introduced in QtOpcUa 5.13.

See also connected(), stateChanged(), setAuthenticationInformation(), and QOpcUaEndpointDescription.

bool QOpcUaClient::deleteNode(const QString &nodeId, bool deleteTargetReferences = true)

Deletes the node with node id nodeId from the server. If deleteTargetReferences is false, only the references with source node nodeId are deleted. If deleteTargetReferences is true, references with nodeId as target are deleted too.

Returns true if the asynchronous call has been successfully dispatched.

The success of the operation is returned in the deleteNodeFinished() signal.

The following example code deletes a node and all references to it from the server:

m_client->deleteNode(QOpcUaExpandedNodeId("ns=3;s=MyNewVariableNode"), true);

See also addNode() and deleteNodeFinished().

bool QOpcUaClient::deleteReference(const QOpcUaDeleteReferenceItem &referenceToDelete)

Deletes the reference described by referenceToDelete from the server.

Returns true if the asynchronous call has been successfully dispatched.

The success of the operation is returned in the deleteReferenceFinished() signal.

The following example code deletes a reference to a node from the "Objects" folder:

QOpcUaDeleteReferenceItem item;
item.setSourceNodeId(QOpcUa::namespace0Id(QOpcUa::NodeIds::Namespace0::ObjectsFolder));
item.setReferenceTypeId(QOpcUa::nodeIdFromInteger(0, static_cast<quint32>(QOpcUa::ReferenceTypeId::Organizes)));
item.setIsForwardReference(true);
item.setTargetNodeId(QOpcUaExpandedNodeId("ns=3;s=MyNewVariableNode"));
item.setDeleteBidirectional(true);

m_client->deleteReference(item);

See also addReference(), deleteReferenceFinished(), and QOpcUaDeleteReferenceItem.

[invokable] void QOpcUaClient::disconnectFromEndpoint()

Disconnects from the server.

Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.

See also disconnected() and connectToEndpoint().

QOpcUaEndpointDescription QOpcUaClient::endpoint() const

Returns the description of the endpoint the client is currently connected to or was last connected to.

QOpcUaClient::ClientError QOpcUaClient::error() const

Returns the current error state of the client.

Note: Getter function for property error.

bool QOpcUaClient::findServers(const QUrl &url, const QStringList &localeIds = QStringList(), const QStringList &serverUris = QStringList())

Starts an asynchronous FindServers request to read a list of known servers from a server or discovery server at url. Returns true if the asynchronous call has been successfully dispatched.

localeIds can be used to select the language of the application names returned by the request. The format is specified in OPC-UA part 3, 8.4, for example "en" for English, or "de-DE" for German (Germany). If more than one locale ID is specified, the server uses the first match. If there is no match or localeIds is empty, a default locale is chosen by the server.

serverUris may be used to restrict the results to servers with a matching applicationUri in their application description. For example, finding the current URL of the server with the applicationUri "MyPLC", the following call can be used:

client->findServers(discoveryServerUrl, QStringList(), QStringList({"MyPLC"}));

The results are returned in the findServersFinished() signal.

bool QOpcUaClient::isNamespaceAutoupdateEnabled() const

Returns whether autoupdate of the namespace array is enabled.

QStringList QOpcUaClient::namespaceArray() const

Returns the cached value of the namespace array.

The value is only valid after the namespaceArrayUpdated() signal has been emitted.

See also updateNamespaceArray() and namespaceArrayUpdated().

int QOpcUaClient::namespaceAutoupdateInterval() const

Returns the current revised update interval of the namespace array.

See also setNamespaceAutoupdateInterval(int interval).

QOpcUaNode *QOpcUaClient::node(const QString &nodeId)

Returns a QOpcUaNode object associated with the OPC UA node identified by nodeId. The caller becomes owner of the node object.

If the client is not connected, nullptr is returned. The backends may also return nullptr for other error cases (for example for a malformed node id).

QOpcUaNode *QOpcUaClient::node(const QOpcUaExpandedNodeId &expandedNodeId)

Returns a QOpcUaNode object associated with the OPC UA node identified by expandedNodeId. The caller becomes owner of the node object.

If the node is not on the currently connected server, the namespace can't be resolved, the node id is malformed or the client is not connected, nullptr is returned.

See also updateNamespaceArray().

[since QtOpcUa 5.13] QOpcUaPkiConfiguration QOpcUaClient::pkiConfiguration() const

Returns the application's PKI configuration of this QOpcUaClient instance.

This function was introduced in QtOpcUa 5.13.

See also setPkiConfiguration().

QOpcUaQualifiedName QOpcUaClient::qualifiedNameFromNamespaceUri(const QString &namespaceUri, const QString &name, bool *ok = nullptr) const

Attempts to create a qualified name from namespaceUri and the name string name. Returns the resulting qualified name. An empty qualified name is returned if namespaceUri can't be resolved.

ok will be set to true if the namespace URI resolution has been successful. If the namespace URI could not be resolved, ok will be set to false.

[since 6.3] QOpcUaHistoryReadResponse *QOpcUaClient::readHistoryData(const QOpcUaHistoryReadRawRequest &request)

Starts a read raw history request for one or multiple nodes. 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.

The start timestamp, end timestamp, number of values per node, returnBounds and nodes to read can be specified in a QOpcUaHistoryReadRawRequest.

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 two nodes are requested and printed. The result is limited to ten values per node.

QOpcUaHistoryReadRawRequest request(
            { QOpcUaReadItem("ns=1;s=myValue1"), QOpcUaReadItem("ns=1;s=myValue2") },
            QDateTime::currentDateTime(),
            QDateTime::currentDateTime().addDays(-2),
            10,
            true);

QOpcUaHistoryReadResponse *response = m_client->readHistoryData(request);
if (response) {
   QObject::connect(response, &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 QOpcUaClient::readNodeAttributes(const QList<QOpcUaReadItem> &nodesToRead)

Starts a read of multiple attributes on different nodes. The node id, the attribute and an index range can be specified for every entry in nodesToRead.

Returns true if the asynchronous request has been successfully dispatched. The results are returned in the readNodeAttributesFinished() signal.

This read function offers an alternative way to read attributes of nodes which can be used for scenarios where the values of a large number of node attributes on different nodes must be read without requiring the other features of the QOpcUaNode based API like monitoring for value changes. All read items in the request are sent to the server in a single request and are answered in a single response which generates a single readNodeAttributesFinished() signal. This reduces the network overhead and the number of signal slot connections if many different nodes are involved.

In the following example, the display name attribute and the two index ranges "0:2" and "5:7" of the value attribute of the same node and the entire value attribute of a second node are read using a single service call:

QList<QOpcUaReadItem> request;
request.push_back(QOpcUaReadItem("ns=1;s=MyArrayNode",
                                 QOpcUa::NodeAttribute::DisplayName));
request.push_back(QOpcUaReadItem("ns=1;s=MyArrayNode",
                                 QOpcUa::NodeAttribute::Value, "0:2"));
request.push_back(QOpcUaReadItem("ns=1;s=MyArrayNode",
                                 QOpcUa::NodeAttribute::Value, "5:7"));
request.push_back(QOpcUaReadItem("ns=1;s=MyScalarNode));
m_client->readNodeAttributes(request);

See also QOpcUaReadItem and readNodeAttributesFinished().

bool QOpcUaClient::requestEndpoints(const QUrl &url)

Starts an asynchronous GetEndpoints request to read a list of available endpoints from the server at url. Returns true if the asynchronous call has been successfully dispatched.

The endpoint information is returned in the endpointsRequestFinished() signal.

QString QOpcUaClient::resolveExpandedNodeId(const QOpcUaExpandedNodeId &expandedNodeId, bool *ok = nullptr) const

Attempts to resolve expandedNodeId to a node id string with numeric namespace index. Returns the node id string if the conversion was successful.

An empty string is returned if the namespace index can't be resolved or if the identifier part of the expanded node id is malformed. ok will be set to true if the conversion has been successful. If the expanded node id could not be resolved, ok will be set to false.

[since QtOpcUa 5.13] void QOpcUaClient::setApplicationIdentity(const QOpcUaApplicationIdentity &identity)

Sets the application identity for this QOpcUaClient instance to identity.

This function was introduced in QtOpcUa 5.13.

See also applicationIdentity().

void QOpcUaClient::setAuthenticationInformation(const QOpcUaAuthenticationInformation &authenticationInformation)

Sets the authentication information of this client to authenticationInformation.

See also authenticationInformation() and connectToEndpoint().

void QOpcUaClient::setNamespaceAutoupdate(bool isEnabled)

Enables automatic update of the namespace table.

Enabling this will keep the local copy of the namespace table updated automatically. namespaceArrayUpdated will be emitted when the array changed. isEnabled determines if autoupdate is being enabled or disabled.

A subscription will be made on the node on the server to keep track of changes. In case a server does not support subscriptions this will not work and isNamespaceAutoupdateEnabled returns false.

See also namespaceArray() and namespaceArrayUpdated().

void QOpcUaClient::setNamespaceAutoupdateInterval(int interval)

Sets the interval for the namespace table subscription.

The subscription may be revised by the server.

interval determines the interval to check for changes in milliseconds. The default is once per second.

See also namespaceAutoupdateInterval() and QOpcUaClient::setNamespaceAutoupdate(bool isEnabled).

[since QtOpcUa 5.13] void QOpcUaClient::setPkiConfiguration(const QOpcUaPkiConfiguration &config)

Sets the application PKI configuration for this QOpcUaClient instance to config.

This function was introduced in QtOpcUa 5.13.

See also pkiConfiguration().

[since QtOpcUa 5.14] QStringList QOpcUaClient::supportedSecurityPolicies() const

Returns the security policies supported by the used backend.

This function is currently available as a Technology Preview, and therefore the API and functionality provided by the function may be subject to change at any time without prior notice.

This function was introduced in QtOpcUa 5.14.

[since QtOpcUa 5.14] QList<QOpcUaUserTokenPolicy::TokenType> QOpcUaClient::supportedUserTokenTypes() const

Returns the user token types supported by the used backend.

This function is currently available as a Technology Preview, and therefore the API and functionality provided by the function may be subject to change at any time without prior notice.

This function was introduced in QtOpcUa 5.14.

See also QOpcUaUserTokenPolicy::TokenType.

bool QOpcUaClient::updateNamespaceArray()

Requests an update of the namespace array from the server. Returns true if the operation has been successfully dispatched.

The namespaceArrayUpdated() signal is emitted after the operation is finished.

See also namespaceArray() and namespaceArrayUpdated().

bool QOpcUaClient::writeNodeAttributes(const QList<QOpcUaWriteItem> &nodesToWrite)

Starts a write for multiple attributes on different nodes. The node id, the attribute, the value, the value type and an index range can be specified for every entry in nodesToWrite.

Returns true if the asynchronous request has been successfully dispatched. The results are returned in the writeNodeAttributesFinished() signal.

This write function offers an alternative way to write attributes of nodes which can be used for scenarios where the values of a large number of node attributes on different nodes must be written without requiring the other features of the QOpcUaNode based API like monitoring for value changes. All write items in the request are sent to the server in a single request and are answered in a single response which generates a single writeNodeAttributesFinished() signal. This reduces the network overhead and the number of signal slot connections if many different nodes are involved.

In the following example, the Values attributes of two different nodes are written in one call. The second node has an array value of which only the first two elements are overwritten:

QList<QOpcUaWriteItem> request;

request.append(QOpcUaWriteItem("ns=2;s=Demo.Static.Scalar.Double", QOpcUa::NodeAttribute::Value,
                                  23.0, QOpcUa::Types::Double));
request.append(QOpcUaWriteItem("ns=2;s=Demo.Static.Arrays.UInt32", QOpcUa::NodeAttribute::Value,
                                  QVariantList({0, 1, 2}), QOpcUa::Types::UInt32, "0:2"));

m_client->writeNodeAttributes(request);

See also QOpcUaWriteItem and writeNodeAttributesFinished().