MqttPublishMessage 属性

当前的消息的标识符，当质量等级为0的时候，不需要重发以及考虑标识情况
The identifier of the current message, when the quality level is 0, do not need to retransmit and consider the identification situation

是否第一次发送数据信息
Whether to send data information for the first time

当前发布消息携带的mqtt的应用消息，包含主题，消息等级，负载。
The application message of mqtt carried in the current published message, including the subject, message level, and load.