Calling external functions in App Designer

For a final project in a MATLAB class, we're required to create a modular program using App Designer to plot data points. We've written functions in the regular MATLAB Editor that authenticate a call to Twitter's Standard Search API, make the call, and deliver relevant information in variables to plot. All the code runs exactly how we want it to within the MATLAB command window. The trouble we're having is in figuring out how to call our functions within the App Designer. If I go into the "functions" tab within the code browser and try to add a new one, it doesn't let me add a function that doesn't have "app" as one of the input arguments. I heard elsewhere that it should be possible to call functions you've already written using the Editor, but it's unclear where to actually type in the call to these functions. I just want to be able to use the same output variables from the functions we've already written, and display the relevant data using tables and plots in the designer. Any advice on how to do that?

[Eric Sargent]

[Answer is below, but here are a couple comments as well]

There is MATLAB documentation to help answer this:

https://www.mathworks.com/help/matlab/creating_guis/code-and-call-app-functions-in-app-designer.html

https://www.mathworks.com/help/matlab/creating_guis/share-data-across-callbacks-in-app-designer.html

Or you can visit these similar questions:

https://www.mathworks.com/matlabcentral/answers/376645-how-to-use-a-function-that-is-not-in-the-same-folder-as-your-current-folder

https://www.mathworks.com/matlabcentral/answers/390971-how-can-i-set-a-global-variable-in-public-properties-app-designer-that-depends-on-another-one

Answer 1

[Ameer Hamza]

if you have some functions placed in you MATLAB path, it is not necessary to paste them in the app designer code. You can just call them like normal functions. For example I’d you have written a function myFunction In MATLAB editor. You can call it in app designer

function appDesignerFunction(app)
  Output = myFunction(Input);
end

[Wissam Al-Sheikh]

what if I have a previously written function like.

things1 = 'edrewg';
things2 = 'drfehe';
things3 = 'hg';
[output1,output2,output3]=xlsread([things1 thing2 things3]);

the app designer shows me multiple problem with this writeiwise.

[jalel zghonda]

Hello ! I have the same problem, how did you manage to solve it ?

[Helder Barreto]

Hello! I am new on matlab and I am making an app with app designer. I have also to call functions in separated files. So I have for example my file called "Euler.m" and when I am calling in a switch case but the appdesigner give me an warning to change the syntax. Its normal? I need to change something? If you can help me I would be glad,

Best Regards,

Hélder Barreto

[Ameer Hamza]

Barreto, It means that there is also a property in your app named Euler(). It will not cause any error, but it can cause confusion when you are trying to debug.

Answer 2

[Eric Sargent]

There is MATLAB documentation to help answer this:

https://www.mathworks.com/help/matlab/creating_guis/code-and-call-app-functions-in-app-designer.html

https://www.mathworks.com/help/matlab/creating_guis/share-data-across-callbacks-in-app-designer.html

But, to anwer your question here:

This sounds like a general MATLAB question and is not just specific to App Designer. Please see this post about how to use functions from other folders outside of you current directory. This approach will work the same with an App Designer app to call the function.

https://www.mathworks.com/matlabcentral/answers/376645-how-to-use-a-function-that-is-not-in-the-same-folder-as-your-current-folder

The difference is you will (probably) need to define the function outputs as properties of the app, and then reference those properties using "app.<variablename>" in other functions / callbacks within your app.

Please see my answer on this post related to referencing properties within App Designer and/or visit the relevant documentation to learn more:

https://www.mathworks.com/matlabcentral/answers/390971-how-can-i-set-a-global-variable-in-public-properties-app-designer-that-depends-on-another-one

[Gary Gorman]

Eric, i do not understand your comments. The issue of running a function file such as myFunc.m is not at all the same as running functions generally. I have a file myFunc.m in my working directory, the same directory as my app myAPP.mlapp. I can run myFunc.m in livescript from a Matlab window but I cannot run myFunc.m from AppDesigner. It appears that in order to use a file named myFunc.m which contains a function you must do some stuff in AppDesigner to facilitate that use, and that stuff that you must do goes beyond simply calling the function as is done in a livescript window. So what is the special stuff you must do to run a myFunc.m external function in Matlab?

[Gary Gorman]

Never mind, Eric, i see it now. The 'special sauce' needed to run external functions in ".m" files is given by Ameer hamza's answer. In order to run an external function in AppDesigner you must redeclare the external function according to the syntax that Ameer describes. Probs "redeclare" is not the write language but I think it gets the idea across:)

Answer 3

[SilverSurfer]

It is not really clear to me how to call external functions defined in .m files.

I have a function which search for some signals in an excel file. It has as output the list of signals found and as a input it has the full path of the file to read

function signals_final = findsignals(file_to_read)

In order to use it in the app designer I should define a new function using Function > Public function.

By looking at Ameer example it is possibile to declare it with a different name (appDesignerFunction). It is mandatory or can I use the same name as the .m file?. Why the first argument shall be app?

function appDesignerFunction(app)
  Output = myFunction(Input);
end

Going back to my function I could write in the appdesigner

function findsignalsfunc(app)
  Output = findsignals(Input);
end

Declaring in this way the designer get me two warnings

"Argument 'app' is unused. Should this method be Static?"

"The value assigned to variable 'Output' might be unused."

I have just tried to call the function without any declaration in the appdesigner and it works.

[Kelechi Akwataghibe]

By looking at Ameer example it is possibile to declare it with a different name (appDesignerFunction). It is mandatory or can I use the same name as the .m file?.

The external functions declared in .m files are public by default. This means that, they are seen by every class/file in matlab.

Declaring a different function with the same name elsewhere will result in a conflict.

Why the first argument shall be app?

This convention is established by MATLAB App Designer itself and is designed to represent an instance of the app.

Declaring in this way the designer get me two warnings

"Argument 'app' is unused. Should this method be Static?"

"The value assigned to variable 'Output' might be unused."

You can choose to make the method static since it doesn't require the class object 'app'. The following will show you how to: https://www.mathworks.com/matlabcentral/answers/1750735-create-static-method-in-app-designer

Your findsignals() function returns something which is stored in 'Output'. The second warning shows that you haven't yet used this result (Output) elsewhere.

In both cases, you can also choose to surpress the warnings (though not advised).