Why does my method doesn't recognise the variable U that I defined as global?

I wrote a method in the designer app, so that I can call the functions that I need without writting them every time for each button. But I get a little error while executing the third function ( in the for =1:numel(U)) line:

methods (Access = public)
        
        function implement = loadingdata(app)  % first function for loading data
                load data.mat Table1
                load data.mat Table2   
 ..      end
        
        function input = timeandfrequency(app) % 2nd function for the input windows
             answer = questdlg('Is there a time stamp?',...
                'Please give the time stamp',...
                'yes','no','no');
                if (answer == "yes") 
                prompt ={' type the start time in [HH:MM:SS] ','Type the endtime in [HH::MM:SS]'};
                dlgtitle = 'Time in HH:MM:SS';
                dims =[1 40];
                definput = {'13:20:00','13:50:00'}; 
                time_answer = inputdlg(prompt,dlgtitle,dims,definput);
                st = time_answer{1,:};
                et = time_answer{2,:};
                end
                answer = questdlg(' Which Frequency would you like to plot ?', ...
                '', ...
                'Frequency 1','Frequency 2','Frequency 3','Frequency 3');
        end
        
        function plotting = diagrams(app) % third function for plotting the data
        for k = 1:numel(U)
        
            Var = Variableunits.Variable;
            Num = size(Var,1);
            X = T.Variable==U(k);
            Uhrzeit = round(seconds(T.Time(X)/1000)); %Umwandlung der Uhrzeit zum Format HH:MM:SS
            Uhrzeit.Format='hh:mm:ss';
            Uhrzeit = sort( Uhrzeit,'ascend');
            Wert = T.Value(X);
            if (answer == "yes") % Wenn ein Zeitstempel vorhanden ist
                ind = find(Uhrzeit >= st & Uhrzeit <= et);%Die Uhrzeit zwischen Anfangsuhrzeit und Endzeit einschränken
                Uhrzeit = Uhrzeit(ind);
                Wert = Wert(ind);
            end
            switch answer
                    case 'Frequency  1'
                    ....
                    case 'Frequency 2'            
                    ....
                    case 'Frequency 3' 
                    ....
            end %switch
        end %for
        end %function 
        end %method

After executing the first button as an example, it calls the 3 function and then I get the error: Unrecognised function or variable U in the method, despite defining it as a global variable below:

      % Button pushed function: Variable1Button
        function H2_TEMPERATURE_Pt01CelsiusButtonPushed(app, event)    
             loadingdata(app)  % first function
            timeandfrequency(app)% second function
            global  Us
            global U; 
            Us = ["Variable1"];
            U = categorical(Us); 
            %for loop
            diagrams(app) % third function

Why does the function cant recognise the variable U? How can the method recognises it from the button function?

Answer 1

[Adam Danz]

Don't use Global variables, especially in AppDesigner!

Instead, declare variables that are shared between app functions as private or public properties.

Private properties are for variables shared interally within the app. Public properties are for variables shared externally to the mlapp file.

See Matlab's documentation on app properties

https://www.mathworks.com/help/matlab/creating_guis/share-data-across-callbacks-in-app-designer.html

Step 1: Declare the variable as a private|public property.

Add the property using the green "+" in the image below (in code view, within AppDesigner)

A private | public declaration will be automatically added to the code. Change the name of "Property" to the variable name.

It's also a good idea to give the variable a default value. I named the variable "myDescriptiveVariableName" and set it as NaN.

Step 2: Use the variable anywhere in the app

To use this variable, simply use app.myDescriptiveVariableName. Any function can update the value stored in that property.

For public variables accessed outside of the app, you just need the app handle and then you can access the variable in the same way as shown above.

Here are some reviews about how to get the app handle outside of the app

• Matlab's documentation
• 3 ways to access your app handle (answers forum)
• 2 ways to access your app handle (answers forum)
• Community Highlight (scroll down to "Review: How to get the handle to an app figure")

[Ramo Rafsel]

Thank you Adam for the detailed answer. I added properties for all the variables that I have. There is just one problem is that the code does not plot properly. Along with the code that I added above (see the comment below:

   nexttile
            yyaxis left
            plot(app.ftime,app.freq)
            hold on
            yyaxis right
            plot(app.Uhrzeit,app.Wert); % I get an error on this line: 
            % Data inputs must match the axis configuration. A numeric axis must have numeric data inputs or data inputs which can be converted to double.
            for i = 1:Num
                if app.Var(i) == app.U(k)
                     app.thisunit = app.Unit(i);
                    if ismissing(app.thisunit)
                        thisunitname = '';
                    else
                        thisunitname = string(app.thisunit);
                    end
                    legend('Variable','Frequency');
                    title(string(app.Var(i)) + " " + thisunitname + " 10^" + string(app.NKS(i)), 'Interpreter', 'none');
                end
            end
            hold off
        end
    end
    end

What does the reason might be for the error?

[Adam Danz]

It suggests that this line

plot(app.ftime,app.freq)

produces a plot from numeric data (as opposed to logical, categorical, etc) but this line

plot(app.Uhrzeit,app.Wert);

contains non-numeric data that needs to be converted to numeric.

These lines below will tell you the class of the data

class(app.Uhrzeit)
class(app.Wert)

[Ramo Rafsel]

Hi Adam. I know I have been asking so many questions lately, and I am really thankful for your immense help. I just feel like I am making it really worse that the code does not even plot anymore:

        case 'Frequency  1'
            app.freq1 = double(split(string(app.freq1(1:end-1)) , ","));
            app.freq = double (app.freq1(:,1));
            app.ftime=linspace(app.Uhrzeit(1),app.Uhrzeit(end-1),height(table(app.freq1table)));
%           app.ftime=app.ftime';
            app.ftime = app.ftime(1:end-1);
            app.ftime = round(seconds(app.ftime/1000)); 
            app.ftime.Format='hh:mm:ss';

Thanks to those two lines you ve written that tell which class has each data, I found out that even though I added the round function for the app.ftime variable and converted it to the 'hh:mm:ss" format. the app.ftime variable has a struct class data and I am not quite sure what is the cause for this. Which I guess gives the error to the plot(app.ftime,app.freq) line:

Error using plot

Invalid data argument.

How can I force a variable (in this case app.ftime ) to be converted to a duration type so that I can be able to plot it (on the x-axis)?

Thanks you so much Adam. I hope this is my last question for now XD, in case I should open a new question about this or it is not okay putting another question in here, let me know

[Adam Danz]

I don't have enough information to understand what's wrong with the snippet of code you shared in your comment above. There are some curious parts in there such as the conversion of app.freq1 (whatever that is) to string and then to double. Plus I don't see the plotting code and how these variables contirbute to the plot.

> the app.ftime variable has a struct class data and I am not quite sure what is the cause for this

Neither am I! Perhpas one of the matlab functions you're using is shadowed by a custom function or scripts with the same name. Maybe app.ftime becomes a structure later in the code.

% This line assigns a vector of numbers to app.ftime.  
% It's unclear why you're creating a table in the 3rd argument
app.ftime=linspace(app.Uhrzeit(1),app.Uhrzeit(end-1),height(table(app.freq1table)));

% This line converts the row vector to a column vector
% It could be combined with the first line above.
% app.ftime=app.ftime';

% This removes the last value 
% Another way of doing that is app.ftime(end)=[];
app.ftime = app.ftime(1:end-1);

% This converts the numeric column vector to a duration in 
% seconds, rounded.
app.ftime = round(seconds(app.ftime/1000)); 

% This changes the displayed format
app.ftime.Format='hh:mm:ss';

What you need to do is learn how to use debug mode so you can explore the variables in each line.

• https://www.mathworks.com/help/matlab/matlab_prog/debugging-process-and-features.html
• https://blogs.mathworks.com/loren/2007/12/07/useful-debugging-commands-and-tips/
• https://www.mathworks.com/matlabcentral/answers/552733-plotting-results-in-array-of-a-while-loop#comment_909634

[Jason Brown]

This is straightforward and I've tried to implement it by loading a time series image in startupFcn and then send the image stack to properties for availability to other functions in the app. However, the image stack is emtpy coming from properties. Like this:

        % Code that executes after component creation
        function startupFcn(app)
            % preload image frame number
            app.FramemEditField.Value = 1;
            app.FrameEditField_2.Value = 1;
            app.FrameEditField.Value = 1;
            % configure image axes
            app.ImageAxes.Visible = 'on';
            app.ImageAxes_2.Visible = 'on';
            app.ImageAxes_3.Visible = 'on';
            app.ImageAxes_5.Visible = 'on';
            app.ImageAxes_7.Visible = 'on';
            
            filterspec = {'*.det', '.det files'};
            [f, p] = uigetfile(filterspec);
            if (ischar(p))
                fname = [p f];
                [detfile_hg, detfile_lg, frametype, counter, trigger, frameindex] = ReadDet(fname, 4680, 200, 3, 1);
                
            end

and then I add the outputs to properties, like this:

    properties (Access = public)
        % Description: store the .det file
        detfile_hg;
        detfile_lg;
        frametype;                    
    end

but when I call them from another function, something like a LoadImageButton_aoiPushed function using this call:

detfile = permute(app.detfile_hg, [2 1 3]);

the variable is empty. Where have I gone wrong?

Thanks in advance

[Adam Danz]

You're not storing the value to the app properties. You're storing the to variables that have the same name as the app properties but those variables are cleared at the end of the function.

[detfile_hg, detfile_lg, frametype, counter, trigger, frameindex] = ReadDet

this should be

[app.detfile_hg, app.detfile_lg, app.frametype, counter, trigger, frameindex] = ReadDet(...)

Also, those properties are only defined when p is a char so think about setting default values when you declare the properties

    properties (Access = public)
        % Description: store the .det file
        detfile_hg  = 0; % for example...
        ...                    
    end

Answer 2

[Théophane Dimier]

you need to redeclare "global U" at the beginning your 3rd function, to create a variable "U" in that functions's workspace and to "synchronize" it with the other "U" variable

see the first example of the doc: https://ch.mathworks.com/help/matlab/ref/global.html?searchHighlight=global&s_tid=srchtitle

[Théophane Dimier]

but anyway, passing the variable U as an argument of the 3rd function would certainly be safer. As a general practice, global variable should be avoided as much as possible.