NaN Error in "App Designer"

Hey guys,

I try to write a simple app that shows me websites in my local browser, I evaluate them with one click and then the next page is loaded. In each step my selection should be written "ratedURLs", which is stored in data_rated.mat. Now the problem is that when I load data_rated.mat into my Matlab workspace, all my values are displayed as "NaN". It is correct that my selection is a string and not a number, but it should not really matter?

classdef manuel_rating_app < matlab.apps.AppBase

    % Properties that correspond to app components
    properties (Access = public)
        UIFigure              matlab.ui.Figure
        HilightButton         matlab.ui.control.Button
        VerypositivButton     matlab.ui.control.Button
        PositivButton         matlab.ui.control.Button
        NeutralButton         matlab.ui.control.Button
        PoorButton            matlab.ui.control.Button
        BadButton             matlab.ui.control.Button
        VeryBadButton         matlab.ui.control.Button
        StatusEditFieldLabel  matlab.ui.control.Label
        StatusEditField       matlab.ui.control.EditField
    end

    properties (Access = public)
        URL % Description
        NewsData
        RatedURLs
    end

    methods (Access = public)

        function writeData(app,status)
            app.RatedURLs(app.URL,1) = status;
            ratedURLs = app.RatedURLs;
            save('data_rated.mat');
            app.URL = app.URL + 1;
            app.StatusEditField.Value = "Aktuelle Webseite: " + num2str(app.URL);
            web(app.NewsData(app.URL,3),'-browser');
        end

    end

    methods (Access = private)

        % Code that executes after component creation
        function startupFcn(app)
            try
            load('data.mat','newsData')
            app.URL = 1;
            app.NewsData = newsData;
            app.StatusEditField.Value = "Loading succeeded";
            web(newsData(1,3),'-browser');
            catch ERROR
                error = ERROR.message;
                app.StatusEditField.Value = error;
                drawnow;
            end
        end

        % Button pushed function: VerypositivButton
        function VerypositivButtonPushed(app, event)
            writeData(app,"very Positiv")
        end

        % Button pushed function: HilightButton
        function HilightButtonPushed(app, event)
            writeData(app,"Highlight")
        end

        % Button pushed function: PositivButton
        function PositivButtonPushed(app, event)
            writeData(app,"Positiv")
        end

        % Button pushed function: NeutralButton
        function NeutralButtonPushed(app, event)
            writeData(app,"Neutral")
        end

        % Button pushed function: PoorButton
        function PoorButtonPushed(app, event)
            writeData(app,"Poor")
        end

        % Button pushed function: BadButton
        function BadButtonPushed(app, event)
            writeData(app,"Bad")
        end

        % Button pushed function: VeryBadButton
        function VeryBadButtonPushed(app, event)
            writeData(app,"very Bad")
        end
    end

    % App initialization and construction
    methods (Access = private)

        % Create UIFigure and components
        function createComponents(app)

            % Create UIFigure
            app.UIFigure = uifigure;
            app.UIFigure.Position = [100 100 739 962];
            app.UIFigure.Name = 'UI Figure';

            % Create HilightButton
            app.HilightButton = uibutton(app.UIFigure, 'push');
            app.HilightButton.ButtonPushedFcn = createCallbackFcn(app, @HilightButtonPushed, true);
            app.HilightButton.Position = [81 835 197 103];
            app.HilightButton.Text = 'Hilight';

            % Create VerypositivButton
            app.VerypositivButton = uibutton(app.UIFigure, 'push');
            app.VerypositivButton.ButtonPushedFcn = createCallbackFcn(app, @VerypositivButtonPushed, true);
            app.VerypositivButton.Position = [81 701 197 103];
            app.VerypositivButton.Text = 'Very positiv';

            % Create PositivButton
            app.PositivButton = uibutton(app.UIFigure, 'push');
            app.PositivButton.ButtonPushedFcn = createCallbackFcn(app, @PositivButtonPushed, true);
            app.PositivButton.Position = [81 571 197 103];
            app.PositivButton.Text = 'Positiv';

            % Create NeutralButton
            app.NeutralButton = uibutton(app.UIFigure, 'push');
            app.NeutralButton.ButtonPushedFcn = createCallbackFcn(app, @NeutralButtonPushed, true);
            app.NeutralButton.Position = [81 441 197 103];
            app.NeutralButton.Text = 'Neutral';

            % Create PoorButton
            app.PoorButton = uibutton(app.UIFigure, 'push');
            app.PoorButton.ButtonPushedFcn = createCallbackFcn(app, @PoorButtonPushed, true);
            app.PoorButton.Position = [81 311 197 103];
            app.PoorButton.Text = 'Poor';

            % Create BadButton
            app.BadButton = uibutton(app.UIFigure, 'push');
            app.BadButton.ButtonPushedFcn = createCallbackFcn(app, @BadButtonPushed, true);
            app.BadButton.Position = [81 180 197 103];
            app.BadButton.Text = 'Bad';

            % Create VeryBadButton
            app.VeryBadButton = uibutton(app.UIFigure, 'push');
            app.VeryBadButton.ButtonPushedFcn = createCallbackFcn(app, @VeryBadButtonPushed, true);
            app.VeryBadButton.Position = [82 50 197 103];
            app.VeryBadButton.Text = 'Very Bad';

            % Create StatusEditFieldLabel
            app.StatusEditFieldLabel = uilabel(app.UIFigure);
            app.StatusEditFieldLabel.HorizontalAlignment = 'right';
            app.StatusEditFieldLabel.Position = [378 471 40 22];
            app.StatusEditFieldLabel.Text = 'Status';

            % Create StatusEditField
            app.StatusEditField = uieditfield(app.UIFigure, 'text');
            app.StatusEditField.Editable = 'off';
            app.StatusEditField.Position = [433 471 274 22];
        end
    end

    methods (Access = public)

        % Construct app
        function app = manuel_rating_app

            % Create and configure components
            createComponents(app)

            % Register the app with App Designer
            registerApp(app, app.UIFigure)

            % Execute the startup function
            runStartupFcn(app, @startupFcn)

            if nargout == 0
                clear app
            end
        end

        % Code that executes before app deletion
        function delete(app)

            % Delete UIFigure when app is deleted
            delete(app.UIFigure)
        end
    end
end

Answer 1

[Kanishk]

Hi @Florian Falk

When debugging the code with a breakpoint on line 26, it appears that "app.RatedURLs" is being updated with "NaN" values at line 25:

25: app.RatedURLs(app.URL,1) = status
26: ratedURLs = app.RatedURLs

This issue arises because the "RatedURLs" property has not been initialized in the properties section. As a result, MATLAB initializes this property to an empty double ([]). Consequently, when attempting to assign string values to this property within the function, it results in "NaN" values.

To resolve this issue, you can restrict the "RatedURLs" property to accept string values by declaring it as such in the properties section. Here is an example of how you can achieve this:

properties (Access = public)
    URL % Description
    NewsData
    RatedURLs string
end

You can read more about initializing property values by referring to the following link.

https://www.mathworks.com/help/matlab/matlab_oop/initialize-property-values.html