Paho从on_message回调中更新用户数据

问题描述

基本上，我希望我的用户数据充当全局标志，该标志在on_message()回调的连续执行之间被读取和更新。我编写并运行了以下脚本：

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,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，我将主题IvanHu发行了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.

但是，这是我得到的：

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

很明显，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？

解决方法

您似乎错过了文档中有关更新user_data对象的内容

稍后可以使用user_data_set（）函数对其进行更新。

摘自文档here

这意味着您需要将新值传递给set_userdata()，因此应如下所示：

# 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)

,

我无法找到一种使用userdata方法满足我的要求的方法，但是我能够使用全局变量方法做到这一点。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,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,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.

,

您必须在连接前通过 client.user_data_set 为 userdata 赋予初始值，然后您可以在 on_message 回调中更新 userdata。

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,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,60)

client.loop_forever()