(App Designer) Dropdown menu detect variables in workspace.

I'm try to familiar myself with apps designer. How to create a dropdown menu with the list of variables in workspace. so, user only choose their selected variable/dataset.

[Stephen23]

Note that your code will be simpler and more robust when data is passed between functions, e.g. as input/output arguments, nested functions, or using guidata. Magically accessing variable in other workspace is always slow, complex, and liable to bugs. Read this to know more:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

Answer 1

[Ameer Hamza]

Yes, it is possible. Here is one way. Add a drop-down menu to the app. In the COMPONENT BROWSER right-click app.UIFigure and add a startupFcn callback for figure object. You can define the newly created function like this

function startupFcn(app)
  vars = evalin('base', 'whos');
  cell_array = cell(size(vars));
  for i=1:length(vars)
    cell_array{i} = vars(i).name;
  end
  app.DropDown.Items = cell_array;
end

where DropDown is the name of your drop-down menu. Now start the app, the drop-down menu will enlist all the variables from the workspace.

[Saiful Adham Shukor]

Thank You Ameer Hamza. I need this one. tqsm again

[Ameer Hamza]

You are welcome.

Answer 2

[Abdelmalek Benaimeur]

thank you so much Ameer Hamza please I have a question

i tried the method you gave us and it worked, but the problem i found is when i open the app i've made, and when i add a new matrix in the workspace it doesn't show up automatically in the dropdown menu until i close the app and re-open it again

is there a way to solve this problem please?

[Ameer Hamza Khan]

One way is to use timer callback. You can use a timer to automatically update the menu at regular (say after every 1 second). Instead of writing my code in startupFcn() you can create a new function inside your app, paste this code in it and assign that function to a timer as callback.

Answer 3

[Abdelmalek Benaimeur]

please could you show me how, beacause i'm new to appdesigner and i didnt' figure out how to do it

[Ameer Hamza Khan]

The attached file contain an example code. In summary i created a property and a callback function.

properties (Access = private)
    menu_timer % Description
end

methods (Access = private)
    
    function update_menu(app, ~, ~)
        vars = evalin('base', 'whos');
        cell_array = cell(size(vars));
        for i=1:length(vars)
            cell_array{i} = vars(i).name;
        end
        app.DropDown.Items = cell_array;
    end
end

and added following figure startup and close functions:

function startupFcn(app)
    app.menu_timer = timer('ExecutionMode', 'fixedRate', ...
        'Period', 1, ...
        'TimerFcn', @app.update_menu);
    start(app.menu_timer);
end

% Close request function: UIFigure
function UIFigureCloseRequest(app, event)
    stop(app.menu_timer);
    delete(app.menu_timer);
    delete(app)
end

Answer 4

[Abdelmalek Benaimeur]

you are the Best, Ameer, thank you so much

[Ameer Hamza Khan]

You are welcome.