Dot indexing not supported in App Designer start up Fcnb

Hello, hope you're good.

i'm creating a multi window app where de dialog window recibes a number as an numeryc entry block, the value is stored (as app.PP.param.TP401) in a mainapp's property when the user closes it. I As the dialog window information is reseted when the user open it again, i want to display the users previusly set value in a label (app.label ). For that i'm using the following code:

function startupFcn(app, AcetonePlant)
           app.PP=AcetonePlant;     % Set the property for the calling app
           a=app.PP.param.TP401;    % Extracts the interest value
           if (isnumeric(a))==1     % Evaluates if the value was already set by the user and displays it. If not, sets not applicable. 
               app.Label.Text = num2str(app.PP.param.TP401);
               return
           else
                app.Label.Text = 'N/A'
           end
end

But it throws me an error saying:

Dot indexing is not supported for variables of this type.

Error in xP401/startupFcn (line 40)

a=app.PP.param.TP401.value;

Error using matlab.apps.internal.GraphicsCallbackProxy/runCallbackFunction (line 23)

Error while evaluating GraphicsCallbackProxy CallbackFcn.

where xP401 is the filename of the dialog window.

I have been trying to solve this problemn for several hours but i couldn't. So i would like you to help me with this, please.

Good bye and thank you in advance

[Mohammad Sami]

What is the struct Acetone plant ? For your code to work acetone plant must be a structure with field param and so on.

[Sebastian Zapata Loaiza]

Hi, Mohammad.

As mentioned on the official documentation: https://www.mathworks.com/help/matlab/creating_guis/creating-multiwindow-apps-in-app-designer.html it´s suggested that the Dialog window app recieves the Main app application data as an input while its initiliazation. Then, AcetonePlant is the filename of the main app.

Yes, param is being saved as field within AcetonePlant app as shown next:

    properties (Access = public)
       param    % Save the parameters to be used during each unit operation subrutine
       res      % Save the results of each unit operation subrutine.
    end

And the TP401 (a numeric entry) value is indexed to param when the user push a buttom from the Dialog window app as follows:

 % Button pushed function: SaveButton
        function SaveButtonPushed(app, event)
            app.AcetonePlant.param.TP401=app.TP401.Value;
        end

[Mohammad Sami]

Have you initialised the property param in the main app on startup. Otherwise it would be an empty variable.

[Mohammad Sami]

If you leave it uninitialised, you will then have to use the function isstruct to verify the param is a structure and isfield to verify that it has a field TP401 before accessing it.

[Mario Malic]

As Mohammad already mentioned, initialise your properties with the known class.

a = struct(); % for structure 
a = []; % for numeric array
a = ''; % for char array

% AccetonePlant is not property of the app as you did not create it
app.AcetonePlant.param.TP401=app.TP401.Value; 

Save callback button is a bit messy, if you're refering to properties as 'app.propertyname', you have to declare that property as 'propertyname'

properties (Access = public)
       param    % Save the parameters to be used during each unit operation subrutine
       res      % Save the results of each unit operation subrutine.
       PP=struct(); % if AcetonePlant is struct
    end

In callback, refer to it

    % Button pushed function: SaveButton
        function SaveButtonPushed(app, event)
            app.PP.param.TP401=app.TP401.Value; % See the TP401.Value, what is this? 
                                                % is this a numeric field in App Designer
                                                % if it is, leave the EditField text next to it,
                                                % so one can know what is it, otherwise, someone
                                                % would guess it's structure with field 'Value'
        end

This code might not solve your problem, but might give you an idea with variables, properties and passing them around the app.