Question

我遇到了这个问题，当我调用on_message时，我的msg.topic方法将无法正常工作。我没有收到错误消息，但是尽管正在发送新消息，但打印语句不再执行。

出什么问题了？

import paho.mqtt.client as client

hostname = 'iot.eclipse.org'
topic = 'Mein/Topic'

def on_message(client, userdata, msg):
    msg = msg.payload.decode()
    print("topic:", msg.topic)
    print("Received Message:      {}".format(msg))

def on_connect(client, userdata, flags, rc):
    print("Connection returned result: " + str(rc) +
          "\n")
    if rc == 0:
        print("Listening now.\n")
    client.subscribe(topic)

client = client.Client()
client.on_message = on_message
client.on_connect = on_connect
client.connect(hostname)
client.loop_forever()

Answer 1

paho客户端具有内置的try / expect块，该块将对on_message的调用包装起来，以防止行为不当的回调使网络线程崩溃。

如果您想知道代码在哪里失败，可以在on_message函数内部添加自己的try / expect以显示问题。像这样：

def on_message(client, userdata, msg):
    try:
        msg = msg.payload.decode()
        print("topic:", msg.topic)
        print("Received Message:      {}".format(msg))
    expect Exception, e:
        print(e)

无法在MQTT客户端中调用message.topic？

1 个答案: