Call an attribute from a Matlab script in AppDesigner GUI

I have created a GUI with app designer which launch a matlab program after the user chose a file and pressed launch button :

function LaunchButtonPushed(app, event)

    
    app.ResultWindowTextArea.BackgroundColor = 'green';
        
    app.ResultWindowTextArea.FontSize = 20;
        
    app.ResultWindowTextArea.Value = 'Launch of the program ...';
        
    testLectureXML(app.FileTextArea.Value{:});
        
    if n_component == 0
             
        app.ResultWindowTextArea.BackgroundColor = 'red';
                 
        app.ResultWindowTextArea.Value = 'Please choose a valid File !';
                 
        stop testLectureXML()
        
    end

end

n_component is an attribute in my testLectureXML matlab program and he is equal to 0 only if the file that the user chose is empty. But it's like my application doesn't recognize n_component as the attribute of my testLectureXML program.

And if possible, if n_component = 0 i would like to stop the program

How can i do this ? Thanks !

Edit : To stop the programm i have thinking of creating

exitProgram = 0 and if exitProgram = 1 return 0

and in the GUI code i just put exitProgram = 1 if the file is empty but i don't know how to access to an attribute of a matlab script with GUI code.