MQTT：如何发送消息而无需调用loop_forever（）

Question

一段时间以来，我一直在使用MQTT来监视我订阅的某些频道。 现在，我想实现发送一条消息作为对状态的反应。 我使用下面的代码运行它，在这里我只在on_message回调（最后的代码1）中做出反应。 但是这段代码使用

loop_forever()

在被阻止的主要代码中。

我想做的只是向MQTT发送一条消息。 当我尝试以下操作（使用所有不同的循环功能）时，MQTT服务器未收到任何消息：

import paho.mqtt.client as mqtt

if __name__ == "__main__":

    mqtt_client = mqtt.Client()
    mqtt_client.connect("192.168.178.204", 1883, 60)
    mqtt_client.username_pw_set(username="test", password="test")

    mqtt_client.publish(topic='TEST', payload='CCCCCCCCC', retain=False)
    mqtt_client.loop_write()
    # mqtt_client.loop()
    # mqtt_client.loop_start()    

    mqtt_client.disconnect()

我如何发送消息到MQTT而不阻塞该进程？

---

代码1：

import paho.mqtt.client as mqtt

def on_connect(client, userdata, rc):
    topic_list = [("TEST_MS", 1)]
    if rc == 0:
        print("Successful connected and subscribed to: {}".format(topic_list))
    client.subscribe(topic_list)


def on_message(client, userdata, msg):
    print(msg.payload)
    client.publish(topic='TEST_MS2', payload=msg.payload, retain=False)


def on_publish(client, userdata, mid):
    print("message published")


def on_subscribe(mosq, obj, mid, granted_qos):
    print("Subscribed: " + str(mid) + " " + str(granted_qos))

if __name__ == "__main__":

    mqtt_client = mqtt.Client()

    mqtt_client.on_connect = on_connect
    mqtt_client.on_message = on_message
    mqtt_client.on_publish = on_publish
    mqtt_client.on_subscribe = on_subscribe

    mqtt_client.connect("192.168.178.204", 1883, 60)
    mqtt_client.username_pw_set(username="test", password="test")

    # mqtt_client.publish(topic='TEST_MS', payload='CCCCCCCCC', retain=False)
    mqtt_client.loop_forever()

    mqtt_client.disconnect()

Answer 1

如果您只想发送一条消息然后退出，请使用专用于此的API。 文件在这里

import paho.mqtt.publish as publish

publish.single("paho/test/single", "payload", hostname="iot.eclipse.org")