How do I write to a MQTT topic through a callback function from subscribe()?

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Toni Ceciro Oconer 2022-4-16

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https://ww2.mathworks.cn/matlabcentral/answers/1698150-how-do-i-write-to-a-mqtt-topic-through-a-callback-function-from-subscribe

回答： Toni Ceciro Oconer 2022-4-17

Hi!

I am working on a project that uses MQTT, however I have run into an issue regarding writing to a topic through a callback function.

Here is a sample code of my problem below

mqttClient = mqttclient('tcp://192.168.1.100:1883')

helloTopic = subscribe(mqttClient,"topic/Hello",QualityOfService=2,callback=@showMessage);

function showMessage(topic,data)

disp(topic);

disp(data);

write(mqttClient,"topic/Goodbye","Bye!");

end

The code runs perfectly fine and displays the topic as well as the data from the topic. However, once it gets to this part of the code:

write(mqttClient,"topic/Goodbye","Bye!");

I get the following error message

Warning: Error occurred while executing the listener callback for event Custom defined for class

matlabshared.asyncio.internal.Channel:

Error using icomm.mqtt.Subscription/handleCustomEvent

Invalid callback function "showMessage" for input arguments of type string.

Error in icomm.mqtt.Subscription>@(varargin)obj.handleCustomEvent(varargin{:})

Error in matlabshared.asyncio.internal.Channel/onCustomEvent (line 497)

notify(obj, 'Custom', matlabshared.asyncio.internal.CustomEventInfo(type,data));

Error in matlabshared.asyncio.internal.Channel>@(source,data)obj.onCustomEvent(data.Type,data.Data) (line

413)

@(source, data) obj.onCustomEvent(data.Type, data.Data));

> In matlabshared.asyncio.internal/Channel/onCustomEvent (line 497)

In matlabshared.asyncio.internal.Channel>@(source,data)obj.onCustomEvent(data.Type,data.Data) (line 413)

Which I'm not sure how to decipher. Am I not allowed to publish to a topic through a callback function from subscribe?

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Answer 1

Toni Ceciro Oconer 2022-4-17

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1698150-how-do-i-write-to-a-mqtt-topic-through-a-callback-function-from-subscribe#answer_944465

Clearing the mqttClient before adding the write() function solved my problem

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