Error using MQTT callbacks in AppDesigner

Question

Bruno Brandão 2019-5-11

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/461521-error-using-mqtt-callbacks-in-appdesigner

回答： Martijn 2020-5-12

I am trying to communicate with a MQTT broker inside a app but my callback functions don't run.

It gives me the following error: Invalid callback function 'myMQTT_RdAllPow_Callback' for input arguments of type 'string'.

The code is bellow:

app.myMQTT = mqtt(mqttServerAddr,'Username','test','Password','test','Port',1883);
subscribe_regCallback(app, app.myMQTT);
app.ConnectedLamp.Color = 'green';
app.NotConnectedLabel.Text = 'Connected';
while 1
    publish(app.myMQTT, 'VGA/RdAllPow', '1');
    pause(5);
end
function subscribe_regCallback(app,myMQTT)
    app.RdAllPow = subscribe(myMQTT, 'VGA/RdAllPow', 'QoS', 0, 'Callback', @myMQTT_RdAllPow_Callback);
end
function myMQTT_RdAllPow_Callback(app,~)
            app.ConnectedLamp.Color = 'yellow';

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Answer 1

Martijn 2020-5-12

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/461521-error-using-mqtt-callbacks-in-appdesigner#answer_431956

在 MATLAB Online 中打开

If you wish to use a private method of an App Designer App as callback, please define your callback by referring to @app.myCallbackMethod. Further, make sure then that myCallbackMethod has a function signature:

function myCallbackMethod(app, input1AsNormallyExpectedByCallback, input2AsNormallyExpectedByCallback, inputNAsNormallyExpectedByCallback, etc)

So in your specific case:

function subscribe_regCallback(app,myMQTT)
    % Refer to @app.myMQTT_RdAllPow_Callback
    app.RdAllPow = subscribe(myMQTT, 'VGA/RdAllPow', 'QoS', 0, 'Callback', @app.myMQTT_RdAllPow_Callback);
end
% For a MQTT callback two inputs are expected, make sure you 
% really define them both and also add app as first input
function myMQTT_RdAllPow_Callback(app,topic,data)
            app.ConnectedLamp.Color = 'yellow';