问题
Is anyone has a logical explanation why despite I have the clear session flage = false I do not receive the updated published message I am subscribed to while i am not connected to the broker?
With the aorementioned flag set to false I ran my App, And i kept publishing to a topic some values (from the PC to the broker not from the Android device to the broker). And then I unpluged the usb of the Android Device frm the pc, and kept publishing some values again. When I plugged the usb to the pc again, i expected to see the values I recently published to that topic, but I did not receive any.
The topic I am publishing to is exactly the topic i am subscribed to, with QoS = 1.
回答1:
In order for messages to be queued for a client that is no longer connected to a broker, these things must be true:
- Client must have originally connected with
clean sessionset to false - Client must have subscribed with QoS>0
- Messages to that topic must have been published with QoS>0
- When the client reconnects it must have the same
client idas when it disconnected - When the client reconnects it must have
clean sessionset to false
My bet is that you are failing on either of the latter two points.
回答2:
You need to send the messages with the retain flag to be able to recieve the messages when you re-connect. The QoS defines how hard the broker/client will try to ensure that a message is received.
Have a read here http://mosquitto.org/man/mqtt-7.html on QOS, clean session and retained messages.
来源：https://stackoverflow.com/questions/26971783/with-the-clear-session-flag-set-to-false-i-am-missing-the-published-values