在调用 int mqtt_subscribe时；如果订阅后立即有数据下发，可能会出现无法接收到该数据帧的情况，这可能是订阅操作与消息处理机制之间的时序问题。可以在此函数调用MQTTSerialize_subscribe之前，先调用mqtt_msg_handler_create函数，如订阅失败再调用mqtt_msg_handler_destory，通过这种方式，可以确保在订阅动作执行前，消息处理机制已正确配置。个人意见，仅供参考
When calling int mqtt_subscribe; If data is delivered immediately after subscribing, there may be a situation where the data frame cannot be received, which may be a timing issue between the subscription operation and the message processing mechanism. You can call the mqtt_msg_handler_create function before this function calls MQTTSerialize_subscribe, and then call mqtt_msg_handler_destory if the subscription fails. This way, you can ensure that before the subscription action is executed, The message handling mechanism is configured correctly. Personal opinion, for reference only
在调用 int mqtt_subscribe时；如果订阅后立即有数据下发，可能会出现无法接收到该数据帧的情况，这可能是订阅操作与消息处理机制之间的时序问题。可以在此函数调用MQTTSerialize_subscribe之前，先调用mqtt_msg_handler_create函数，如订阅失败再调用mqtt_msg_handler_destory，通过这种方式，可以确保在订阅动作执行前，消息处理机制已正确配置。个人意见，仅供参考
When calling int mqtt_subscribe; If data is delivered immediately after subscribing, there may be a situation where the data frame cannot be received, which may be a timing issue between the subscription operation and the message processing mechanism. You can call the mqtt_msg_handler_create function before this function calls MQTTSerialize_subscribe, and then call mqtt_msg_handler_destory if the subscription fails. This way, you can ensure that before the subscription action is executed, The message handling mechanism is configured correctly. Personal opinion, for reference only