MQTT:无法订阅Qt中的主题

#include <QCoreApplication>
#include <QtMqtt/QMqttClient>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QtMqtt::QMqttClient client("qt_mqtt_client");

    // 连接信号槽
    QObject::connect(&client, &QtMqtt::QMqttClient::connected, [&]() {
        qDebug() << "Connected to MQTT Broker";
        client.subscribe(QMqttTopicName("test/topic"));
    });

    QObject::connect(&client, &QtMqtt::QMqttClient::subscribed, [&](const QString &topic) {
        qDebug() << "Subscribed to topic:" << topic;
    });

    QObject::connect(&client, QOverload<const QList<QMqttSubscription> &>::of(&QtMqtt::QMqttClient::subscriptionsChanged),
                     [&](const QList<QMqttSubscription> &subscriptions) {
                         qDebug() << "Subscriptions changed";
                     });

    // 连接到MQTT Broker
    client.connectToHost();

    return a.exec();
}