How can I use the if statement with a down drop in app designer?

I am making an app in which I calculate the value of a length with the angle and angular velocity provided by the user, I placed a down drop for w with two options: rpm and rad / s. In order to carry out the calculations I need the unit to be in rad /s.

The error that occurs when running the app is that in the lines of the variables z3C, z4C, z1C says that it does not recognize the variable w2.

I would appreciate your help.

% Callbacks that handle component events
    methods (Access = private)

        % Value changed function: DropDownW2
        function DropDownW2ValueChanged(app, event)
            uniw2 = app.DropDownW2.Value;
            if strcmp(uniw2,'rpm')
                wa2=app.w2.Value;
                w2 = (2*pi*wa2)/60;
            else
                w2 = app.w2.Value;
            end
        end

        % Button pushed function: CalcularButton
        function CalcularButtonPushed(app, event)
            a2 = app.a2.Value;
            w3 = app.w3.Value;
            a3 = app.a3.Value;
            w4 = app.w4.Value;
            a4 = app.a4.Value;
            
            %Calular en complejos
            z2C = w4*((w3^2)*j+a3)-w3*((w4^2)*j+a4);
            z3C = w2*(a4+(w4^2)*j)-w4*(a2+(w2^2)*j);
            z4C = w3*((w2^2)*j+a2)-w2*((w3^2)*j+a3);
            z1C = -z2C-z3C-z4C;

Answer 1

[Jemima Pulipati]

Hello,

From my understanding, you are not able to access the variables defined in one callback in another callback within the same app.

You have to use 'Properties' to access variables across functions and callbacks. You can either create a Public or Private Property, the process is explained here but here are the steps described briefly:

1. From the editor tab in App Designer, select the red option 'Property' dropdown button at the top and select "Private Property". This will add a property definition to a properties block in the code.
2. Within that newly added section, you can define any variable name that you want to use across callbacks, in your case 'w2' (see section 1 below)
3. In your 'DropDownW2ValueChanged()' function, use 'app.' to reference this variable (declared in property) and assign some value. (see section 2)
4. Now when you want to access this variable in any other callback use the same 'app.' to reference it. (see section 3)

% Section 1
properties (Access = private)
    w2 = 0; % This variable is expected to be used across different callbacks
end
    
% Section 2
function DropDownW2ValueChanged(app, event)
    app.w2 = (2*pi*wa2)/60; % Assigning values to the property variable declared for this app
end

% Section 3
function CalcularButtonPushed(app, event)
    z3C = app.w2*(a4+(w4^2)*j)-w4*(a2+(app.w2^2)*j); % Using the same property variable in calculations
end

So, this means any property variable has to be referenced using 'app.' .This ensures the variable is present in the scope which is common to all callbacks / functions in the app.

NOTE: This property variable name should be unique. It should not be the same as any another property variables defined in another app and being passed to this app.

[Ana Lopez]

I was traying put to put the variable in the properties but it did not set the variable to zero, so I got this error 'Error using matlab.ui.control.internal.model.Abstract Numeric Component / set.Value (line 111)' Value 'must be a double scalar 'later. But this solved the problem and the app works as I want. Thanks you so much

[JUNGCHENG WU]

how did you solve the problem with ''Error using matlab.ui.control.internal.model.Abstract Numeric Component / set.Value (line 111)' Value 'must be a double scalar '????