How can I set a global variable in public properties App Designer that depends on another one?

Dear all,

I have a problem on understanding how properly set a global variable in App Designer.

Indeed, I am using App Designer that at the button pressing will run a waving sinusoid in the UIaxes. Since this sinusoid will be called in another function I want that its parameters are usable and visible also in other functions.

I saw in other guides that to do this the variable can be set in the Public properties. However if I write:

    properties (Access = public)
           Fs = 60;                   % samples per second
           dt = 1/Fs;                 % seconds per sample
           StopTime = 60;             % seconds
           t = (0:dt:StopTime-dt)';   % seconds
           Fc = 0.47;
           x = 300*sin(2*pi*Fc*(t))+((app.BWEditField.Value+20)*9.81); % Starting wave

    end

As you can see, I would keep global and visible all the parameters that allows to build a sinusoid. However, when I run, it gives an error on dt because it says that it doesn't find Fs. It seems like that it does not run in line the code...

Simplyfing. The question is: How can I declare globally in the properties the variables X and Y, with Y that is defined using X?

Answer 1

[Steven Lord]

When defining properties' default values, you can only use the values of other properties if those properties are Constant. To access them you need to use the name of the class, which for purposes of this answer I'll call myappclass.

    properties (Access = public, Constant)
           Fs = 60;                   % samples per second
           dt = 1/myappclass.Fs;                 % seconds per sample
           StopTime = 60;             % seconds
           t = (0:myappclass.dt:myappclass.StopTime-myappclass.dt)';   % seconds
           Fc = 0.47;

Those properties can be given values in the definition as they don't depend on the state of a particular instance of the class. The last property you tried to define cannot be given a default value in the properties block as it depends on the state of a particular instance of the class. You can define this property but you can't give it a value here. You could set its value in the constructor or in a regular method.

           x = 300*sin(2*pi*Fc*(t))+((app.BWEditField.Value+20)*9.81); % Starting wave

    end

Answer 2

[Eric Sargent]

You need to define them as public properties and set the static values. You need to declare ALL of the variables you want/need to use in subsequent functions within the app.

[update]

Note, in the comments below, "app.tend" is used in StartupFcn but "tend" is not defined in properties)

properties (Access = public)
     Fs = 60;                   % samples per second
     StopTime = 60;             % seconds
     Fc = 0.47;
     dt;
     t;
     x;
end

Then initialize the dependent variables in a startupFcn callback and refer to each of the variables as "app.<variablename>", such as:

function startupFcn(app)
     app.dt = 1/app.Fs;                                                      % seconds per sample
     app.t = (0:app.dt:app.StopTime-app.dt)';                                % seconds
     app.x = 300*sin(2*pi*app.Fc*(app.t))+((app.BWEditField.Value+20)*9.81); % Starting wave 
end

Use the same dot notation in your subsequent code to access those variables.

plot(app.UIAxes,app.t,app.x)

[Alessandro Frongia]

Hi Eric!

Firstly, thanks a lot for your reply. I followed what you said and i wrote Properties and Startup function in this way (some variables changed but it's not that the problem, the question remained the same):

    properties (Access = public)
            Fs = 60;           % sample frequency
            tpuls = 5;         % length of chirp
            StopTime = 60; 
            a = udp('','LocalHost','','LocalPort',5000); % Description
    end

    methods (Access = public)

        function startupFcn(app)

             app.dt = 1/app.Fs;                     % seconds per sample
             app.t =  (0:app.dt:app.tpuls)';           % seconds
             app.tend =  (0:app.dt:app.StopTime)';     % seconds
            %      app.t =  0:0.0167:5;
            %      app.tend =  0:0.0167:60;
             app.endvector = app.StopTime/app.tpuls;

        end

Now, running my code through App Designer it says:

No appropriate method, property, or field 'tend' for class 'SailingTrainer'.

What does it mean? I mean, the error seems still in the declaration of the parameters that must be shared among all the functions. Indeed, for example tend is the time vector of the final signal and it gives errors if I press a Run button to plot the signal. t instead is the time vector of a portion of that signal who goes to form it with some iterations. This one give the same error once is called is formation through a Drop Down menu...

I am a bit confused...if I put as you told me, and if, where needed, i call them app.* (* stays for the name of the variable), why is still giving errors? I specify that the Access is public both in properties and in startupfcn...

[Alessandro Frongia]

Just in case, here below is my current code. Briefly, I will explain what it has to do. The DropDown menu creates for each option a small random loop that merges repeated chirp signals (ystep, with t as time vector) in a final one (y, with tend as time vector). The loop includes just a way to create randomly the type of chirp. After that the other parameters are just a Edit field to insert a parameter who will change the offset of the signal and a slider who will increase the same offset by a percentage of the Edit field value. The rest is just 2 buttons, one to start and one to stop the plot of this signal, who has a rolling animation from right to left in the UI figure... Therefore, time vectors and the parameters to build the signal must be available for the various functions...

Here below the code:

classdef SailingTrainer < matlab.apps.AppBase

    % Properties that correspond to app components
    properties (Access = public)
        UIFigure               matlab.ui.Figure
        UIAxes                 matlab.ui.control.UIAxes
        RunButton              matlab.ui.control.Button
        StopButton             matlab.ui.control.Button
        BWEditFieldLabel       matlab.ui.control.Label
        BWEditField            matlab.ui.control.NumericEditField
        ScenarioDropDownLabel  matlab.ui.control.Label
        ScenarioDropDown       matlab.ui.control.DropDown
        TrainingLevelLabel     matlab.ui.control.Label
        TrainingLevelSlider    matlab.ui.control.Slider
    end

    properties (Access = public)
            Fs = 60;           % sample frequency
            tpuls = 5;         % length of chirp
            StopTime = 60; 
            a = udp('','LocalHost','','LocalPort',5000); % Description
            y;
    end

    methods (Access = public)

        function startupFcn(app)

             app.dt = 1/app.Fs;                     % seconds per sample
             app.t =  (0:app.dt:app.tpuls)';           % seconds
             app.tend =  (0:app.dt:app.StopTime)';     % seconds
            %      app.t =  0:0.0167:5;
            %      app.tend =  0:0.0167:60;
             app.endvector = app.StopTime/app.tpuls;

        end

    end

    methods (Access = private)

        % Value changed function: ScenarioDropDown
        function ScenarioDropDownValueChanged(app, event)
            scenario = app.ScenarioDropDown.Value;

            switch scenario

                      case 'Calm'
                      
                         f0 = 0.4;
                         f1 = 0.7;

                         app.y = chirp(app.t, f0, app.t(end), f1,'linear');
                         sizechirp_vec=size(app.y);
                         sizechirp=sizechirp_vec(1,2);

                                for i = 1:(endvector-1)

                                    mod = randi(3,1);
                                    switch mod
                                    case 1
                                     type = 'linear';
                                    case 2
                                     type = 'logarithmic';
                                    case 3
                                     type = 'quadratic';   
                                    end  

                                ystep= chirp(app.t, f0, app.t(end), f1,type);
                                app.y=[app.y,ystep(1:(sizechirp-1))];

                                end

                                   app.y(app.y<0) = 0;
                                   app.y = (20)*sign(app.y)+(app.BWEditField.Value+30);

                case 'Choppy'
                      
                         f0 = 0.5;
                         f1 = 0.9;

                         app.y = chirp(app.t, f0, app.t(end), f1,'linear');
                         sizechirp_vec=size(app.y);
                         sizechirp=sizechirp_vec(1,2);

                                for i = 1:(endvector-1)

                                    mod = randi(3,1);

                                    switch mod
                                    case 1
                                     type = 'linear';
                                    case 2
                                     type = 'logarithmic';
                                    case 3
                                     type = 'quadratic';   
                                    end  

                                ystep= chirp(app.t, f0, app.t(end), f1,type);
                                app.y=[app.y,ystep(1:(sizechirp-1))];

                                end

                                   app.y(app.y<0) = 0;
                                   app.y = (30)*sign(app.y)+(app.BWEditField.Value+30); 

                case 'Open water'
                      
                         f0 = 0.6;
                         f1 = 0.8;

                         app.y = chirp(app.t, f0, app.t(end), f1,'linear');
                         sizechirp_vec=size(app.y);
                         sizechirp=sizechirp_vec(1,2);

                                for i = 1:(endvector-1)

                                    mod = randi(3,1);
                                    switch mod
                                    case 1
                                     type = 'linear';
                                    case 2
                                     type = 'logarithmic';
                                    case 3
                                     type = 'quadratic';   
                                    end  

                                ystep= chirp(app.t, f0, app.t(end), f1,type);
                                app.y=[app.y,ystep(1:(sizechirp-1))];                                   

                                end

                                   app.y(app.y<0) = 0;
                                   app.y = (40)*sign(app.y)+(app.BWEditField.Value+30);

            end

        end

        % Button pushed function: RunButton
        function RunButtonPushed(app, event)
            n=0;                   %initialization                         
            i=1;
            % 1 n = 3 seconds (???)

            endcycle=30;
            while (n<endcycle)    %n decides the length of the recording (keep on mind that in the future it must be coherent with a start-stop system

            fopen(app.a);

            u.DatagramTerminateMode = 'off';
            data = fscanf(app.a);
            fclose(app.a);

            results = str2num(data);            % it takes the ASCII string from the bench and it puts the values in an array
            results_array (i,:) = results;       % it splits the data from the 4 sensors
            %results_Newton = results_array*9.81; % conversion from Kg to N

            Fsbv = results_array(:,1);         % These are the 4 separated forces from each sensor
            Fbbv = results_array(:,2);
            Fbba = results_array(:,3);
            Fsba = results_array(:,4);

            Ftot = Fsbv+Fbbv+Fbba+Fsba;         % Total force

             plot(app.UIAxes,app.tend,app.y,'r',0,Ftot(i),':bo',...            
    'LineWidth',1,...
    'MarkerSize',8,...
    'MarkerEdgeColor',[0,0,0.5],...
    'MarkerFaceColor',[1,0.6,0])
        xlim(app.UIAxes,[-2 2])
        ylim(app.UIAxes,[30 200])

            i=i+1;
            n=n+1;

        % Delaying animation

                app.t=app.t-10*app.dt;

            drawnow limitrate 

            end
        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 1184 798];
            app.UIFigure.Name = 'UI Figure';
            setAutoResize(app, app.UIFigure, true)

            % Create UIAxes
            app.UIAxes = uiaxes(app.UIFigure);
            app.UIAxes.Box = 'on';
            app.UIAxes.Position = [78 87 1091 536];

            % Create RunButton
            app.RunButton = uibutton(app.UIFigure, 'push');
            app.RunButton.ButtonPushedFcn = createCallbackFcn(app, @RunButtonPushed, true);
            app.RunButton.BackgroundColor = [0.1059 0.8196 0.1059];
            app.RunButton.FontName = 'Tahoma';
            app.RunButton.FontSize = 24;
            app.RunButton.FontWeight = 'bold';
            app.RunButton.FontColor = [1 1 1];
            app.RunButton.Position = [12 686 165 36];
            app.RunButton.Text = 'Run';

            % Create StopButton
            app.StopButton = uibutton(app.UIFigure, 'push');
            app.StopButton.BackgroundColor = [0.8196 0.1059 0.1059];
            app.StopButton.FontName = 'Tahoma';
            app.StopButton.FontSize = 24;
            app.StopButton.FontWeight = 'bold';
            app.StopButton.FontColor = [1 1 1];
            app.StopButton.Position = [12 632 165 39];
            app.StopButton.Text = 'Stop';

            % Create BWEditFieldLabel
            app.BWEditFieldLabel = uilabel(app.UIFigure);
            app.BWEditFieldLabel.HorizontalAlignment = 'right';
            app.BWEditFieldLabel.Position = [124 14 25 15];
            app.BWEditFieldLabel.Text = 'BW';

            % Create BWEditField
            app.BWEditField = uieditfield(app.UIFigure, 'numeric');
            app.BWEditField.Limits = [0 Inf];
            app.BWEditField.ValueDisplayFormat = '%11.3g';
            app.BWEditField.HorizontalAlignment = 'center';
            app.BWEditField.Position = [164 10 65 22];
            app.BWEditField.Value = 80;

            % Create ScenarioDropDownLabel
            app.ScenarioDropDownLabel = uilabel(app.UIFigure);
            app.ScenarioDropDownLabel.HorizontalAlignment = 'right';
            app.ScenarioDropDownLabel.Position = [992 18 54 15];
            app.ScenarioDropDownLabel.Text = 'Scenario';

            % Create ScenarioDropDown
            app.ScenarioDropDown = uidropdown(app.UIFigure);
            app.ScenarioDropDown.Items = {'Calm', 'Choppy', 'Open water'};
            app.ScenarioDropDown.ValueChangedFcn = createCallbackFcn(app, @ScenarioDropDownValueChanged, true);
            app.ScenarioDropDown.Position = [1061 14 100 22];
            app.ScenarioDropDown.Value = 'Calm';

            % Create TrainingLevelLabel
            app.TrainingLevelLabel = uilabel(app.UIFigure);
            app.TrainingLevelLabel.HorizontalAlignment = 'right';
            app.TrainingLevelLabel.Position = [12 10 67 28];
            app.TrainingLevelLabel.Text = {'+/- Training'; 'Level (%)'};

            % Create TrainingLevelSlider
            app.TrainingLevelSlider = uislider(app.UIFigure);
            app.TrainingLevelSlider.Limits = [0 20];
            app.TrainingLevelSlider.MajorTicks = [0 5 10 15 20];
            app.TrainingLevelSlider.Orientation = 'vertical';
            app.TrainingLevelSlider.Position = [17 63 3 178];
        end
    end

    methods (Access = public)

        % Construct app
        function app = SailingTrainer()

            % Create and configure components
            createComponents(app)

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

            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