Paho 从 on_message 回调中更新用户数据

Question

基本上，我希望我的用户数据充当全局标志，在 on_message() 回调的连续执行之间读取和更新。我写了运行以下脚本：

import paho.mqtt.client as mqtt
MQTT_SERVER = "broker.hivemq.com"
MQTT_TOPIC = "IvanHu"

# The callback for when the client receives a CONNACK response from the server.
def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))
    client.subscribe(MQTT_TOPIC)
    
# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
    print(userdata, end = '')
    print(" message received.")
    userdata += 1
    user_data_set(client_userdata)

client_userdata = 1

client = mqtt.Client(userdata=client_userdata)
client.on_connect = on_connect
client.on_message = on_message
client.connect(MQTT_SERVER, 1883, 60)

client.loop_forever()

然后我在IvanHu这个话题上发表了4次。我希望我的 python paho 脚本的输出如下：

Connected with result code 0
1 message received.
2 message received.
3 message received.
4 message received.

然而，这是我得到的：

Connected with result code 0
1 message received.
1 message received.
1 message received.
1 message received.

显然，变量 client_userdata 从未在连续的 on_message() 调用中得到更新。更新此变量的正确方法是什么？

Answer 1

您似乎错过了文档中关于更新 user_data 对象的内容

It may be updated at a later point with the user_data_set() function.

取自文档here

这意味着您需要将新值传递给 set_userdata()，因此它应该如下所示：

# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
    print(userdata, end = '')
    print(" message received.")
    userdata += 1
    client.user_data_set(userdata)

Answer 2

我找不到使用用户数据方法来满足我的要求的方法，但我可以使用全局变量方法来满足我的要求。这是工作脚本：

import paho.mqtt.client as mqtt
MQTT_SERVER = "broker.hivemq.com"
MQTT_TOPIC = "IvanHu"

# The callback for when the client receives a CONNACK response from the server.
def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))
    client.subscribe(MQTT_TOPIC)
    
# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
    global client_userdata
    print(client_userdata, end = '')
    print(" message received.")
    client_userdata += 1

client_userdata = 1

client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message
client.connect(MQTT_SERVER, 1883, 60)

client.loop_forever()

输出：

Connected with result code 0
1 message received.
2 message received.
3 message received.
4 message received.

Answer 3

你必须在连接前client.user_data_set给用户数据一个初始值，然后你可以在on_message回调中更新用户数据。

import paho.mqtt.client as mqtt
MQTT_SERVER = "broker.hivemq.com"
MQTT_TOPIC = "IvanHu"

# The callback for when the client receives a CONNACK response from the server.
def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))
    client.subscribe(MQTT_TOPIC)
    
# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
    print(userdata, end = '')
    print(" message received.")
    user_data_set(userdata + 1)    # <-- Update userdata

client_userdata = 1

client = mqtt.Client(userdata=client_userdata)
client.on_connect = on_connect
client.on_message = on_message
client.user_data_set(1)    # <-- Initialize
client.connect(MQTT_SERVER, 1883, 60)

client.loop_forever()

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