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MQTT subscribe callback function not executed in AppDesigner

Asked by Alberto Franzini on 21 Feb 2019
Latest activity Commented on by Alberto Franzini on 21 Feb 2019
I am developing a graphic user interface on AppDesigner with the purpose of displaying the result of a classification algorithm using data coming via MQTT protocol. The “subscribe” function (related to the “mqtt” function) requires the use of a callback to perform tasks whenever data are received. This procedure works fine when applied outside AppDesigner, while within AppDesigner it seems like the callback function is never executed. An attempt to address this issue was using global variable (see code below) but it did not work.
function StartButtonPushed(app, event)
% Connection to MQTT
mqttAddress = 'tcp://10………';
mObj = mqtt(mqttAddress,'Port',1883);
mySub = subscribe(mObj,'sensors','callback',@appCallback);
function appCallback(~,~)
app.GoodLamp.Color = 'Green';
How can this issue be addressed?


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1 Answer

Answer by Sean de Wolski
on 21 Feb 2019
 Accepted Answer

(This is a guess)
When the function exits, the mObj and mySub are destroyed. Set them to be properties of the app (add properties and then app.mObj = ...) so that they exist after the function call completes.

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