Learn from Taiji makers - mqtt (V) publish, subscribe and unsubscribe

Video link ：https://www.bilibili.com/video/BV1G541157NZ/?spm_id_from=333.788.recommend_more_video.-1&vd_source=b91967c499b23106586d7aa35af46413

Tutorial links ：http://www.taichi-maker.com/homepage/esp8266-nodemcu-iot/iot-tuttorial/mqtt-tutorial/publish-subscribe-unsubscribe-mqtt-msg/

Learn how the client can publish messages 、 Subscribe to topics and unsubscribe from topics

PUBLISH – Release the news

sometimes , A client to MQTT The interval for the server to publish new messages on the topic is long , Maybe a few days or more , under these circumstances , If our client subscribes to a topic , It may take a long time , So in order to solve this problem , Just set up retainFlag This mechanism , When the client sends to the server PUBLISH In the message , If retainFlag Set to ture when , When the client subscribes to a topic , Will immediately receive this set to ture This message of . In other words, ,MQTT The server will retainFlag Set to true Of PUBLISH The message content is saved , The purpose of preservation is whenever , As long as a client subscribes to this topic message , The server will immediately send the subject message to the client .

SUBSCRIBE – Subscribe to topics

SUBACK – Subscription confirmation

UNSUBSCRIBE – Unsubscribe

The following is the practice .

1、 Client connection MQTT Server side

2、 Client subscription topics chantui

Again , You can click on several topics .

3、 The client sends a message named chantui The theme of the news release

Click on publish after ,