python - paho-MQTT python : How to let the loop_forever support subscribe message?

Question

我已经在 paho-mqtt 上测试了示例程序，并且我知道函数 Loop_forever() 可以处理重新连接。但我的问题是，虽然loop_forever()可以重新连接，但它不能重新订阅。应该是服务器突然崩溃的时候出现问题，此时客户端还在监听，但是当服务器重新启动后，客户端可以重新连接，但不能再订阅消息了。我想也许我应该重写loop_forever()函数，但我不确定我是否正确，以及如何做到这一点。

import sys
try:
    import paho.mqtt.client as mqtt
except ImportError:
    # This part is only required to run the example from within the examples
    # directory when the module itself is not installed.
    #
    # If you have the module installed, just use "import paho.mqtt.client"
    import os
    import inspect
    cmd_subfolder = os.path.realpath(os.path.abspath(os.path.join(os.path.split(inspect.getfile( inspect.currentframe() ))[0],"../src")))
    if cmd_subfolder not in sys.path:
        sys.path.insert(0, cmd_subfolder)
    import paho.mqtt.client as mqtt

def on_connect(mqttc, obj, flags, rc):
    print("rc: "+str(rc))

def on_message(mqttc, obj, msg):
    print(msg.topic+" "+str(msg.qos)+" "+str(msg.payload))

def on_publish(mqttc, obj, mid):
    print("mid: "+str(mid))

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

def on_log(mqttc, obj, level, string):
    print(string)

# If you want to use a specific client id, use
# mqttc = mqtt.Client("client-id")
# but note that the client id must be unique on the broker. Leaving the client
# id parameter empty will generate a random id for you.
mqttc = mqtt.Client()
mqttc.on_message = on_message
mqttc.on_connect = on_connect
mqttc.on_publish = on_publish
mqttc.on_subscribe = on_subscribe
# Uncomment to enable debug messages
#mqttc.on_log = on_log
mqttc.connect("m2m.eclipse.org", 1883, 60)
mqttc.subscribe("$SYS/#", 0)


mqttc.loop_forever()

Answer 1

处理此问题的简单方法是在 on_connect 回调中进行订阅，然后当您重新连接时，所有订阅也将恢复。