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// Copyright (C) 2018 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*!
\example subscriptions
\examplecategory {Connectivity}
\title MQTT Subscriptions
\ingroup qtmqtt-examples
\brief Creating a application that communicates with an MQTT broker.
\image subscriptions.png
\e {MQTT Subscriptions} shows how to create an application that communicates
with an MQTT broker. A new dialog opens for each subscription, where you can
see the messages on the subscribed topics.
\section1 Creating a Client
We use the QMqttClient class to create an MQTT client and to set the broker
host name and port to use for the connection:
\quotefromfile subscriptions/mainwindow.cpp
\skipto m_client
\printuntil setPort
\section1 Subscribing to Topics
When users subscribe to topics in the client, a new subscription object is
created:
\skipto on_buttonSubscribe_clicked
\printuntil }
\printuntil }
We use the QMqttSubscription class to store the topic, state, and QoS level
of a subscription:
\quotefromfile subscriptions/subscriptionwindow.cpp
\skipto QMqttSubscription
\printuntil });
\printuntil }
The QoS level can be set separately for a message and for a subscription.
The QoS level set for a subscription determines the minimum QoS level. If
a message is sent with a higher QoS level, the broker increases the QoS of
that message to the higher level. For example, if client A subscribed to
\e topic with QoS 1, and client B publishes a message on the topic, with
QoS 0, the broker will automatically increase the QoS of the message to 1.
If client B publishes a message on the topic with the QoS 2, the broker
will send it with QoS 2.
\section2 Receiving Messages
When the client receives a message, the QMqttMessage class is used to store
the actual message payload:
\skipto updateMessage
\printuntil }
*/
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