Qt Quick 出版物

使用Qt Quick Controls 创建可在 MQTT 主题上发布的应用程序。

Qt Quick 出版物演示了如何将注册为 QML 类型并在应用程序中使用。QMqttClient Qt Quick

Qt MQTT在当前版本中，《MQTT.NET》不提供 QML API。不过，您可以将模块的 C++ 类提供给 QML。

创建客户端

创建以QMqttClient 为成员的封装类QmlMqttClient ：

private:
    Q_DISABLE_COPY(QmlMqttClient)
    QMqttClient m_client;
};

在构造函数中将包装器方法连接到QMqttClient 的方法：

QmlMqttClient::QmlMqttClient(QObject *parent)
    : QObject(parent)
{
    connect(&m_client, &QMqttClient::hostnameChanged, this, &QmlMqttClient::hostnameChanged);
    connect(&m_client, &QMqttClient::portChanged, this, &QmlMqttClient::portChanged);
    connect(&m_client, &QMqttClient::stateChanged, this, &QmlMqttClient::stateChanged);
}

封装方法的名称与被封装方法的名称相同。在最简单的情况下，它只是一个方法调用：

void QmlMqttClient::connectToHost()
{
    m_client.connectToHost();
}

也可以通过扩展一些附加功能来定制封装方法：

voidQmlMqttClient::setPort(intnewPort) {如果（newPort< 0 ||newPort>std::numeric_limits<quint16>::max()) {        qWarning() << "Trying to set invalid port number";
       return; } m_client.setPort(static_cast<quint16>(newPort));

在 QML 中注册类

在main.cpp 文件中，从模块出版物中加载 QML 类型 Main：

    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine;

    QObject::connect(
            &engine, &QQmlApplicationEngine::objectCreationFailed, &app,
            []() { QCoreApplication::exit(EXIT_FAILURE); }, Qt::QueuedConnection);

    engine.loadFromModule(u"publication"_s, u"Main"_s);

现在使用Main.qml 文件中的 MqttClient 类型创建 MQTT 客户端：

    MqttClient {
        id: client
        hostname: hostnameField.text
        port: portField.text
    }

文件：

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