MATLAB App Listbox items not changing

I am trying to modify the default values of a listbox in a Matlab App (Item 1, Item 2...) by using the following code:

            value = app.CountryListBox.Value; %Default value that appears when I created a callback for the listbox
            first_cell_column=covid_data(:,1); %Extract the first column of my cell array, which contains the name of the countries
            first_unique_column=unique(first_cell_column); %Remove repeated names
            countries=(first_unique_column(first_unique_column~="Country")).'; %Remove the tag "country" and transpose my column vector to a row vector (1x195)
            app.CountryListBox.Items=countries; %Assign my cell row vector to the CountryListBox Items object

However, when I run the app, the Listbox remains unchanged, with the same default values. No error or warning appears on the program neither. What am I doing wrong?

Answer 1

[Cris LaPierre]

Where have you placed the code in your app? It appears to be in your listbox ValueChanged callback. That means this function will not execute until you select a different item in your listbox.

Try selecting item2 or item3. Your listbox should update. Or at least this callback funciton will execute.

[Pablo Rodríguez Suárez]

It appeared automatically here:

        % Value changed function: CountryListBox
        function CountryListBoxValueChanged(app, event)
            first_cell_column=covid_data(:,1);
            first_unique_column=unique(first_cell_column);
            countries=(first_unique_column(first_unique_column~="Country")).';
            app.CountryListBoxValueChanged.Items={'countries'};

Right after the StartUpFcn. How do I select item 2 or 3?

[Pablo Rodríguez Suárez]

Ok, it's solved! I put the exact same code on the StartUp function, and it worked. Now I understand what you mean by selecting the second item...Thank you!