为什么我的回调函数不起作用？

Question

这是我的代码。无论我如何尝试，我都无法让回调函数正常工作。当客户端连接或收到消息时，什么也不会发生。我已经尝试了所有不同的循环选项。我能找到的都是我已经尝试过的东西。我已经尝试了网上找到的所有方法，但仍然不起作用。回调函数不会做任何事情。

import json
import time
import paho.mqtt.client as mqtt


# Callback function when the client connects to the MQTT broker
def on_connect(client, userdata, flags, rc):
    print("Connected with result code " + str(rc))
    # Subscribe to a topic when connected (optional)
    client.subscribe("test/topic")

# Callback function when a message is received from the MQTT broker
def on_message(client, userdata, msg):
    print("test")
    print("Received message: " + msg.payload.decode())
    client.disconnect()

# Create an MQTT client instance
client = mqtt.Client()

# Set the callback functions
client.on_connect = on_connect
client.on_message = on_message

# Connect to the MQTT broker (replace broker_address with your broker's IP/hostname)
client.connect("broker_adress", 1234, 60)
print("connected")

# Start the MQTT network loop to process incoming and outgoing messages
client.loop()
print("loop started")

client.subscribe("topic")
print("subscribed")
time.sleep(1)


# Publish a message to a topic (replace test/topic with your desired topic)
client.publish("topic", "Hello, MQTT!")
print("published")
# Wait for a few seconds to receive any messages (you can use time.sleep() for testing purposes)
# For a more robust implementation, you can use client.loop_forever() instead of time.sleep
time.sleep(2)

# Disconnect from the MQTT broker
client.loop_stop()```

Answer 1

根据文档，使用

client.loop()

时，您必须：

定期调用处理网络事件。

给出的例子是：

run = True
while run:
    mqttc.loop()

因此

client.loop()

设计用于已经有循环的情况（例如检查传感器读数），并在每次迭代时调用

client.loop()

（意味着定期调用它）。

我认为您打算使用

client.loop_start()

（基于代码末尾对

client.loop_stop()

的调用）。进行此更改（将

client.loop()

替换为

client.loop_start()

）可能会解决您的问题。

另一种方法是将

client.subscribe("topic")

和

client.publish("topic", "Hello, MQTT!")

移至

on_connect

（

subscribe

呼叫的推荐位置）并使用

client.loop_forever()

Answer 2

1. 检查 MQTT 代理地址：仔细检查您在

   client.connect()

   调用中使用的“broker_address”。确保它是您的 MQTT 代理的正确 IP/主机名和端口。
2. 使用 client.loop_start()：使用

   client.loop()

   代替

   client.loop_start()

   。这将为 MQTT 网络循环启动一个单独的线程，这可以帮助处理传入和传出的消息。
3. 检查连接是否正在建立：调用

   client.connect()

   后，添加一个短暂的延迟，以允许在继续之前建立连接。您可以使用

   time.sleep(1)

   等待一秒钟。
4. 使用 client.loop_forever()：考虑使用

   client.loop_forever()

   ，而不是在几秒钟后手动停止循环。这将使客户端无限期地保持连接并连续处理传入的消息。 .... 现在尝试一下这段代码...

import json
import time
import paho.mqtt.client as mqtt

# Callback function when the client connects to the MQTT broker
def on_connect(client, userdata, flags, rc):
    print("Connected with result code " + str(rc))
    # Subscribe to a topic when connected (optional)
    client.subscribe("test/topic")

# Callback function when a message is received from the MQTT broker
def on_message(client, userdata, msg):
    print("test")
    print("Received message: " + msg.payload.decode())
    client.disconnect()

# Create an MQTT client instance
client = mqtt.Client()

# Set the callback functions
client.on_connect = on_connect
client.on_message = on_message

# Connect to the MQTT broker (replace broker_address with your broker's IP/hostname)
client.connect("broker_adress", 1234, 60)
print("connected")

# Start the MQTT network loop to process incoming and outgoing messages
client.loop_start()
print("loop started")

client.subscribe("topic")
print("subscribed")
time.sleep(1)

# Publish a message to a topic (replace test/topic with your desired topic)
client.publish("topic", "Hello, MQTT!")
print("published")

# Keep the client running and handling incoming messages indefinitely
client.loop_forever()

尝试运行此更新的代码，看看当您连接并接收消息时是否会触发回调函数。如果仍然存在任何问题，请确保您的 MQTT 代理设置正确并且可以通过您的设备进行访问。 另外，检查是否有任何可能阻止连接的潜在防火墙或安全配置。