(PS! Just changing the old topics that had retain back to no retain, did not work, had to make new ones.)

I can’t help much without knowing your setup. What are you seeing on the REPL or serial monitor? What devices and firmware version are you running? Post your code and I’ll see if I can figure out your issue.

Internal FS (FatFS): Mounted on partition 'internalfs' [size: 2031616; Flash address: 0x210000]
----------------
Filesystem size: 1978368 B
           Used: 585728 B
           Free: 1392640 B
----------------
I (497) [TFTSPI]: attached display device, speed=8000000
I (497) [TFTSPI]: bus uses native pins: false
[ M5 ] node id:d8a01d698f30, api key:32532B1C
I (4783) system_api: Base MAC address is not set, read default base MAC address from BLK0 of EFUSE
I (4784) system_api: Base MAC address is not set, read default base MAC address from BLK0 of EFUSE
I (4935) phy: phy_version: 4100, 2a5dd04, Jan 23 2019, 21:00:07, 0, 0
I (4942) modsocket: Initializing
Connect Wi-Fi: SSID:xxxxxxxx PASSWD:xxxxxxxx network...
......
Connected. Network config: ('10.0.0.5', '255.255.255.0', '10.0.0.1', '10.0.0.1')
Warning: Comparison between bytes and str
Warning: Comparison between bytes and str
Warning: Comparison between bytes and str
Traceback (most recent call last):
  File "main.py", line 48, in <module>
  File "flowlib/m5mqtt.py", line 100, in subscribe
  File "flowlib/simple.py", line 193, in subscribe
  File "flowlib/simple.py", line 243, in wait_msg
  File "flowlib/m5mqtt.py", line 52, in _on_data
KeyError: b'sensor/light'
MicroPython v1.11-319-g54c3f2613-dirty on 2020-01-15; ESP32 module with ESP32
Type "help()" for more information.
>>> 

So, subscribing to multiple topics seems to be okay in general, but setting the retain flag = True on more than one of those topics seems to cause the MQTT client to throw an error. Also, with lots of debugging, I found that you can only have one topic that has the retain flag = True and it has to be the last one in your micropython code (I think because the code is processed from the bottom up???).

This code works. Topics aa, bb, cc, and dd have messages with retain=True. Topics aaa, bbb, ccc, and ddd have messages with retain=False. Topic dd is at the bottom.

from m5stack import *
from m5ui import *
from uiflow import *
from m5mqtt import M5mqtt

setScreenColor(0x000000)


m5mqtt = M5mqtt('m5stickC', '10.0.0.60', 1883, 'mqtt', 'password', 300)

label0 = M5TextBox(2, 17, "Text", lcd.FONT_Default,0xFFFFFF, rotate=0)
label1 = M5TextBox(2, 57, "Text", lcd.FONT_Default,0xFFFFFF, rotate=0)
label2 = M5TextBox(2, 96, "Text", lcd.FONT_Default,0xFFFFFF, rotate=0)
label3 = M5TextBox(2, 132, "Text", lcd.FONT_Default,0xFFFFFF, rotate=0)

a = None
b = None
c = None
d = None


def fun_aaa_(topic_data):
  global a, b, c, d
  a = topic_data
  label0.setText(str(a))
  pass
m5mqtt.subscribe(str('aaa'), fun_aaa_)

def fun_bbb_(topic_data):
  global a, b, c, d
  b = topic_data
  label1.setText(str(b))
  pass
m5mqtt.subscribe(str('bbb'), fun_bbb_)

def fun_ccc_(topic_data):
  global a, b, c, d
  c = topic_data
  label2.setText(str(c))
  pass
m5mqtt.subscribe(str('ccc'), fun_ccc_)

def fun_dd_(topic_data):
  global a, b, c, d
  d = topic_data
  label3.setText(str(d))
  pass
m5mqtt.subscribe(str('dd'), fun_dd_)


m5mqtt.start()
while True:
  wait(1)
  wait_ms(2)

This does not work since topic cc (retain=True) is not at the bottom.

from m5stack import *
from m5ui import *
from uiflow import *
from m5mqtt import M5mqtt

setScreenColor(0x000000)


m5mqtt = M5mqtt('m5stickC', '10.0.0.60', 1883, 'mqtt', 'password', 300)

label0 = M5TextBox(2, 17, "Text", lcd.FONT_Default,0xFFFFFF, rotate=0)
label1 = M5TextBox(2, 57, "Text", lcd.FONT_Default,0xFFFFFF, rotate=0)
label2 = M5TextBox(2, 96, "Text", lcd.FONT_Default,0xFFFFFF, rotate=0)
label3 = M5TextBox(2, 132, "Text", lcd.FONT_Default,0xFFFFFF, rotate=0)

a = None
b = None
c = None
d = None


def fun_aaa_(topic_data):
  global a, b, c, d
  a = topic_data
  label0.setText(str(a))
  pass
m5mqtt.subscribe(str('aaa'), fun_aaa_)

def fun_bbb_(topic_data):
  global a, b, c, d
  b = topic_data
  label1.setText(str(b))
  pass
m5mqtt.subscribe(str('bbb'), fun_bbb_)

def fun_cc_(topic_data):
  global a, b, c, d
  c = topic_data
  label2.setText(str(c))
  pass
m5mqtt.subscribe(str('cc'), fun_cc_)

def fun_ddd_(topic_data):
  global a, b, c, d
  d = topic_data
  label3.setText(str(d))
  pass
m5mqtt.subscribe(str('ddd'), fun_ddd_)


m5mqtt.start()
while True:
  wait(1)
  wait_ms(2)

However, if you move the cc topic to the bottom it works again.

from m5stack import *
from m5ui import *
from uiflow import *
from m5mqtt import M5mqtt

setScreenColor(0x000000)


m5mqtt = M5mqtt('m5stickC', '10.0.0.60', 1883, 'mqtt', 'password', 300)

label0 = M5TextBox(2, 17, "Text", lcd.FONT_Default,0xFFFFFF, rotate=0)
label1 = M5TextBox(2, 57, "Text", lcd.FONT_Default,0xFFFFFF, rotate=0)
label2 = M5TextBox(2, 96, "Text", lcd.FONT_Default,0xFFFFFF, rotate=0)
label3 = M5TextBox(2, 132, "Text", lcd.FONT_Default,0xFFFFFF, rotate=0)

a = None
b = None
c = None
d = None


def fun_aaa_(topic_data):
  global a, b, c, d
  a = topic_data
  label0.setText(str(a))
  pass
m5mqtt.subscribe(str('aaa'), fun_aaa_)

def fun_bbb_(topic_data):
  global a, b, c, d
  b = topic_data
  label1.setText(str(b))
  pass
m5mqtt.subscribe(str('bbb'), fun_bbb_)

def fun_ddd_(topic_data):
  global a, b, c, d
  d = topic_data
  label3.setText(str(d))
  pass
m5mqtt.subscribe(str('ddd'), fun_ddd_)

def fun_cc_(topic_data):
  global a, b, c, d
  c = topic_data
  label2.setText(str(c))
  pass
m5mqtt.subscribe(str('cc'), fun_cc_)

m5mqtt.start()
while True:
  wait(1)
  wait_ms(2)

Hope this helps. Also, I hope @m5stack will update the m5mqtt client to support the Retain flag, QoS, and the Last Will and Testament (LWT) messages soon to solve some of these limitations I have uncovered.

Here are my uiFlows:

M5Stack #1 has an ENV unit providing Temperature, Pressure, and Humidity to MQTT, is reading the status of the LIGHT unit from M5Stack #2, and is reading the status of the iPhone app providing fake sensor/thermostat data. M5Stack #2 has a LIGHT unit providing the digital status of the light sensor (on/off) to MQTT, is reading the T/P/H values provided by M5Stack #1, and is reading the status of the iPhone app providing fake sensor/thermostat data.

Troubleshooting the black screen: REPL is your friend for errors. That is ultimately how I figured out what was not working. On a Mac, I opened Terminal and typed this to get to the REPL:
screen -port /dev/tty.SLAB_USBtoUART -b 115200

As I was building the setup, trying a slightly modified flow on each device, I forgot to connect the unit on the other M5stack. If you have a unit added in uiFlow UI (left side panel) and the unit blocks added to your flow, but the unit is not physically connected to the M5stack, this causes a black screen when attempting to connect to MQTT. No on screen error at all, but the REPL said something like "env0 not found" when I rebooted the M5stack and looked at the startup logs. It would just sit there and hang.

Another issue is that the Unit number might be changing on you when you add/remove it from your device or program (i.e. env0 changes to env1 or light0 changes to light1), especially when you don't refresh the entire uiFlow webpage before connecting each new device.

Anyway, I hope this helps someone. If you have other scenarios you want me to test, let me know.

When i send http request:
https://io.adafruit.com/api/v2/robalstona/feeds/feed01

i receive something like that in json format:

{"username":"robalstona","owner":{"id":300855,"username":"robalstona"},"id":1207296,"name":"feed01","description":null,"license":null,"history":true,"enabled":true,"visibility":"public","unit_type":null,"unit_symbol":null,"last_value":"20.7","created_at":"2019-10-27T19:40:47Z","updated_at":"2020-01-23T12:01:53Z","key":"feed01","writable":false,"group":{"id":198443,"key":"default","name":"Default","user_id":300855},"groups":[{"id":198443,"key":"default","name":"Default","user_id":300855}]}

in my case the "last_value" field with assigned value "20.7" is what I need.

You can use JSON->loads json and ADVANCED -> HTTP -> Get Data to store this data in variable as list.

only then do you need to know the structure of this list to get to the field with interesting data values

@world101 Your example does not read the topics, it's being set when you push the buttons....

You are correct. I'm having the same issues as you.

I'm not using HomeAssistant and do not have any real sensors that I'm pulling data from. However, the two topics is working for me when I simulate sensor data with button A and B presses, or when I add the data manually via the AIO feed console.

I'll try to set up HomeAssistant on a RPi and see if anything changes.

@robalstona
So if i try to get the second one also with mqtt subscribe to a different topic (2nd inverter) the hole screen is black. Any hints?

Are there any errors on HomeAssistant? I use Adafruit IO and when I get a black screen due to an issue configuring something in UIFlow , typically I can see some errors on the broker’s web console.

It could be your feed configuration or the sensor data (stored as float or int instead of strings) or something like that.

@buhi It is possible that the problem is how the data is sent to the mqtt server and how often they are sent. In my case, the sensor data is sent every 25 seconds. And if I run this program it will only show me --- until the server receives new data. and then the channel is subscribed, the data are saved to the variable and displayed on the lcd display. So if you have data updated, for example, every hour, nothing may be displayed for an hour. You can combine something with the "retain" flag when sending data to the server, then you will be able to receive the last data received from the feed. But this already needs to be changed on the device / software side that this data sends.

https://mntolia.com/mqtt-retained-messages-explained-example

I opened a request for UIFlow to add support for the retain flag. You can track it here.

https://github.com/m5stack/UIFlow-Code/issues/1

https://mntolia.com/mqtt-retained-messages-explained-example