发布保留消息到主题
问题
你想向代理上的 MQTT 主题发布一条保留消息。
解决方案
在 MQTT Output 节点的配置对话框中将 Retain 选项设置为 true，或者将发送到节点的消息中的 msg.retain 消息属性设置为 true。
示例
[{"id":"4a7dc819.3aa6f8","type":"mqtt out","z":"eda2a949.74ea98","name":"","topic":"sensors/livingroom/temp","qos":"","retain":"true","broker":"61de5090.0f5d9","x":430,"y":420,"wires":[]},{"id":"fb7b873.c391878","type":"inject","z":"eda2a949.74ea98","name":"temperature","topic":"","payload":"22","payloadType":"num","repeat":"","crontab":"","once":false,"x":230,"y":420,"wires":[["4a7dc819.3aa6f8"]]},{"id":"61de5090.0f5d9","type":"mqtt-broker","z":"","broker":"localhost","port":"1883","clientid":"","usetls":false,"compatmode":true,"keepalive":"60","cleansession":true,"willTopic":"","willQos":"0","willPayload":"","birthTopic":"","birthQos":"0","birthPayload":""}]
讨论
一旦你向一个主题发送了保留消息，所有订阅者在订阅时都将收到该消息。
要从代理中清除先前保留的主题，请向该主题发送一个空消息，并设置保留标志。
