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Replace the current license disclaimer in files by a SPDX-License-Identifier. License files are organized under LICENSES directory. Pick-to: 6.4 Task-number: QTBUG-67283 Change-Id: Ie4309963c8e17d4e7dad602f61a660246d5e23cb Reviewed-by: Jörg Bornemann <joerg.bornemann@qt.io>
59 lines
2.0 KiB
Plaintext
59 lines
2.0 KiB
Plaintext
// Copyright (C) 2018 The Qt Company Ltd.
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// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
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/*!
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\example subscriptions
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\title MQTT Subscriptions Example
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\ingroup qtmqtt-examples
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\brief Creating a application that communicates with an MQTT broker.
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\image subscriptions.png
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\e {MQTT Subscriptions} shows how to create an application that communicates
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with an MQTT broker. A new dialog opens for each subscription, where you can
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see the messages on the subscribed topics.
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\section1 Creating a Client
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We use the QMqttClient class to create an MQTT client and to set the broker
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host name and port to use for the connection:
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\quotefromfile subscriptions/mainwindow.cpp
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\skipto m_client
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\printuntil setPort
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\section1 Subscribing to Topics
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When users subscribe to topics in the client, a new subscription object is
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created:
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\skipto on_buttonSubscribe_clicked
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\printuntil }
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\printuntil }
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We use the QMqttSubscription class to store the topic, state, and QoS level
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of a subscription:
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\quotefromfile subscriptions/subscriptionwindow.cpp
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\skipto QMqttSubscription
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\printuntil });
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\printuntil }
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The QoS level can be set separately for a message and for a subscription.
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The QoS level set for a subscription determines the minimum QoS level. If
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a message is sent with a higher QoS level, the broker increases the QoS of
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that message to the higher level. For example, if client A subscribed to
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\e topic with QoS 1, and client B publishes a message on the topic, with
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QoS 0, the broker will automatically increase the QoS of the message to 1.
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If client B publishes a message on the topic with the QoS 2, the broker
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will send it with QoS 2.
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\section2 Receiving Messages
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When the client receives a message, the QMqttMessage class is used to store
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the actual message payload:
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\skipto updateMessage
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\printuntil }
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*/
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