Any way to make a global wrapper code for all callbacks in App Designer?

I am in the process of migrating a GUI I created using GUIDE to App Designer (2019b). In GUIDE, I added code to the main function that would wrap around any action taken using the GUI. The two pieces of functionality I added were:

1. Error handling, so that I could catch any unexpected error in the entire application and print it out to an error log.

2. Changing the cursor to the spin-wheel while any code was being executed, so the user knew that it was still thinking.

I included a simplified excerpt at the bottom of what I had for my main function.

My problem now is that I'm trying to recreate the same functionality in App Designer, but the constructor code is completely locked down and uneditable. Is there a way to create any sort of wrapper code that would have the same effect in App Designer? Maybe a way to overload some function?

try % Setup a try/catch around all callbacks
    % Set the cursor to the spin-wheel
    set(varargin{4}.figure1,'pointer','watch'); % varargin{4} = handles;
    drawnow;

    % Call callback function as normal
    if nargout
        [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
    else
        gui_mainfcn(gui_State, varargin{:});
    end
    
    % Set cursor back to arrow when done
    set(varargin{4}.figure1,'pointer','arrow');
    drawnow;
catch ME
    % Catch unexpected errors, write out to log file, and reset cursor
    reportErrorLog(ME,varargin{4},true);
    set(varargin{4}.figure1,'pointer','arrow');
    drawnow;
    
    % Smoothly exit function with appropriate nargout
    if(nargout)
        varargout(1:nargout)={[]};
    end
end

[Stephen23]

Is there any particular reason why you need to use App Designer, as opposed to just writing your own GUI code?

[David K]

I guess I don't feel knowledgable enough to create one from scratch, and App Designer makes it very easy to adjust the visual layout without having to worry about fixing all the relevant code.

Can you just copy/paste all of the code to a new file and retain all of the functionality, or is there hidden functionality in the .mlapp file?

[Mohammad Sami]

If you are not going to compile as a webapp, you can create the GUI in AppDesigner then export the app as code.

Thereafter you will be able to edit the exported code.