App Designer, how to use value of DropDown in external function file

Hello everyone, currently I am working on App Designer and need to use the DropDown item in order to be able to select which expression I want the calculations to proceed with. I have created a separate .m file which involves an if statement. If the DropDown value (Type) equals 1, do this expression, if it equals 2, then this other. I am getting the following error "Output argument "Rad_fin" (and maybe others) not assigned during call to "OgiveTypeAPP"". I call the outputs on app designer as follows:

[Rad_fin,Rad_tip,Rad_rear,Rad] = OgiveTypeAPP(dist_fin,DIST_tip,DIST_rear,DIST); %All inputs are specified on the app.

On app desginer I have stored the value of the dropdown as:

global Type; Type = app.DropDown.Value;

Below is a screenshot of the settings for the drop down and the external .m function I am using.

function [Rad_fin,Rad_tip,Rad_rear,Rad] = OgiveTypeAPP(l,m,n,o)
    global Rmax
    global L
    global Type
    
    if Type == 1
        Rad_fin = Rmax*sqrt(l/L);
        Rad_tip = Rmax*sqrt(m/L);
        Rad_rear = Rmax*sqrt(n/L);
        Rad = Rmax*sqrt(o/L);
    elseif Type == 2
        Rad_fin = Rmax*(l/L).^(0.75);
        Rad_tip = Rmax*(m/L).^(0.75);
        Rad_rear = Rmax*(n/L).^(0.75);
        Rad = Rmax*(o/L).^(0.75);
    end
end

Answer 1

[Mario Malic]

Quick, delete the line with global variable before MATLAB police comes! Don't use global variables, unless there is really a need for it.

First of all, if you will use your variables in external functions, use the as properties, there is an option called Create property - public and define it.

Rmax = 5; % or Rmax = []

Similarly for char array: Type ='';

You can access or change the property value by typing

app.Rmax

In App designer create a button and a callback. Within it call your external function and pass the whole app (or only needed variables)

ExternalFunction(app)

And within the external function access the variables/properties as mentioned above.

[MLP]

Thank you for your help, I got rid of the global variables!

I had to use the strcmp function and use the ItemData value, I don't really understand why but it works perfectly. Thank you again! Here is how I wrote it in case someone else stumbles upon this question.

function [Rad_fin,Rad_tip,Rad_rear,RAD] = OgiveTypeAPP(l,m,n,o,p,q,s)
    Rmax = p; L = q;
    if (strcmp(s,'1'))                              %Conical                   
        Rad_fin = (Rmax*l)/L;
        Rad_tip = (Rmax*m)/L;
        Rad_rear = (Rmax*n)/L;
        RAD = (Rmax*o)/L;
    elseif (strcmp(s,'2'))                          %Elliptical
        Rad_fin = Rmax*sqrt(1-((l-L).^2)/L^2);
        Rad_tip = Rmax*sqrt(1-((m-L).^2)/L^2);
        Rad_rear = Rmax*sqrt(1-((n-L).^2)/L^2);
        RAD = Rmax*sqrt(1-((o-L).^2)/L^2);

[Mario Malic]

I am not sure why didn't you get an error in your App Designer since Value can only be equal to Items (maybe I am wrong). In your example

DropdownMenu.Items = {'Power Law n = 0.5; Power Law n = 0.75'};
DropdownMenu.Value = 'Power Law n = 0.5'; % Must be one of the Items

ItemsData is a number that is associated with Items, you set there already 1 and 2.

Therefore

DropdownMenu.ItemsData = 1 - corresponds to DropdownMenu.Items{1} = 'Power Law n = 0.5' and DropdownMenu.Value(1) = 'Power Law n = 0.5';