why does appdesigner listbox display so slow?

Hello,

i am working on appdesigner and editing my listbox items inside of a "edit field" call back. If i have a '.' in the string, i delete before the dot and assign it to the listbox item. Listbox items are displayed 20 to 50 seconds later. Is it normal to take that long? How can i make it faster? How can i display the executing time of this callback?

Thank you.

function FilePathEditFieldValueChanged(app, event)
             
            a={ 'string','string2','string3','string4'}; %there are 233 elements in this cell array not 4
            for k=1:length(a)
                if contains(a{1,k},'.')
                 
                    n = split(a{1,k},".");
                    app.Signals1ListBox.Items{end+1} =n{end,1} ;
                    app.Signals2ListBox.Items{end+1} =n{end,1} ;
                else
                    app.Signals1ListBox.Items{end+1} =a{1,k} ; 
                    app.Signals2ListBox.Items{end+1} =a{1,k} ; 
                end
            end
end