QMqttMessage Class

The QMqttMessage class provides information about a message received from a message broker based on a subscription. More...

Header: #include <QMqttMessage>
qmake: QT += mqtt


Public Functions

QMqttMessage(const QMqttMessage &other)
QMqttMessage &operator=(const QMqttMessage &other)
bool duplicate() const
quint16 id() const
const QByteArray &payload() const
QMqttPublishProperties publishProperties() const
quint8 qos() const
bool retain() const
QMqttTopicName topic() const
bool operator!=(const QMqttMessage &other) const
bool operator==(const QMqttMessage &other) const

Detailed Description

An MQTT message is created inside the module and returned via the QMqttSubscription::messageReceived() signal.

Property Documentation

duplicate : const bool

This property holds whether the message is a duplicate.

Duplicate messages indicate that the message has been sent earlier, but it has not been confirmed yet. Hence, the broker assumes that it needs to resend to verify the transport of the message itself. Duplicate messages can only occur if the QoS level is one or two.

Access functions:

bool duplicate() const

id : const quint16

This property holds the ID of the message.

IDs are used for messages with a QoS level above zero.

Access functions:

quint16 id() const

payload : const QByteArray

This property holds the payload of a message.

Access functions:

const QByteArray &payload() const

qos : const quint8

This property holds the QoS level of a message.

Access functions:

quint8 qos() const

retain : const bool

This property holds whether the message has been retained.

A retained message is kept on the broker for future clients to subscribe. Consequently, a retained message has been created previously and is not a live update. A broker can store only one retained message per topic.

Access functions:

bool retain() const

topic : const QMqttTopicName

This property holds the topic of a message.

In case a wildcard has been used for a subscription, describes the topic matching this subscription. This property never contains wildcards.

Access functions:

QMqttTopicName topic() const

Member Function Documentation

QMqttMessage::QMqttMessage(const QMqttMessage &other)

Constructs a new MQTT message that is a copy of other.


Creates a new MQTT message.

QMqttMessage &QMqttMessage::operator=(const QMqttMessage &other)

Makes this object a copy of other and returns the new value of this object.

QMqttPublishProperties QMqttMessage::publishProperties() const

Returns the publish properties received as part of the message.

Note: This function only specifies the properties when a publish message is received. Messages with a QoS value of 1 or 2 can contain additional properties when a message is released. Those can be obtained by the QMqttClient::messageStatusChanged signal.

Note: This function will only provide valid data when the client specifies QMqttClient::MQTT_5_0 as QMqttClient::ProtocolVersion.

This function was introduced in Qt 5.12.

bool QMqttMessage::operator!=(const QMqttMessage &other) const

Returns true if the message and other are not equal, otherwise returns false.

bool QMqttMessage::operator==(const QMqttMessage &other) const

Returns true if the message and other are equal, otherwise returns false.

© 2021 The Qt Company Ltd. Documentation contributions included herein are the copyrights of their respective owners. The documentation provided herein is licensed under the terms of the GNU Free Documentation License version 1.3 as published by the Free Software Foundation. Qt and respective logos are trademarks of The Qt Company Ltd. in Finland and/or other countries worldwide. All other trademarks are property of their respective owners.