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向主题发布保留消息

问题

您想在代理上向MQTT主题发布一条保留消息。

解决方案

MQTT输出节点配置对话框中将Retain选项设置为true,或在发送到节点的消息中将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":"温度","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

一旦您向主题发送了保留消息,所有订阅者在订阅时将收到该消息。

要从代理中清除先前保留的主题,请向该主题发送一条空消息,并将保留标志设置。