MATLAB: Undefined variable in app designer when the variable called in external function

app designer

Below is the code in my first push button
 
[file,filepath,~]=uigetfile('*.xls*','Multiselect','on','Select Vos file');
app.filepath=fullfile(filepath,file);
app.filepathEditField.Value = app.filepath;
Below is the code in second push button where i am trying to call an external function when the second function is pushed
if(isempty(app.filepath))
    
    f = uifigure;
    uialert(f,'Please select all the files','Error');
    
else
  process_function;
end
the two codes above were wrote in appdesigner meanwhile the process function is an .m file
function a = process_function
[~,filename,fileext]=fileparts(app.filepath);
end
But i get the error in app designer showing undefined function of app.filepath. I really have no idea how to solve this, hope someone can give the the solution. Thanks in advance.

Best Answer

Your external function does not know which variables you use in your app. You need to pass them along. Try changing 
else
  process_function(app.filepath);
end
and
function a = process_function(filepath) 
[~,filename,fileext]=fileparts(filepath);
end
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