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

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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

Accepted Answer

Mario Malic
Mario Malic on 14 Sep 2020
Edited: Mario Malic on 15 Sep 2020
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.
  2 Comments
MLP
MLP on 15 Sep 2020
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
Mario Malic on 15 Sep 2020
Edited: Mario Malic on 18 Sep 2020
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';

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