Loading excel file by GUI

I am trying to load an excel file via GUI. The line of code i used in a regular script was:

%%Read excel file to MATLAB
% Select file from prompt (only excel, csv and txt files)
excelfile = uigetfile('*.xlsx;*.csv;*.txt;','Select event file generated by ActivPAL');

From which i later used 'excelfile' for:

TF = strncmpi(excelfile,datefile.ParticipantID,8);
PreIDParticipant = datefile(TF==1,:);

However, when implementing this in the GUI script, i get the error:

Undefined function or variable 'excelfile'.

    Error in TestUI>Calculation_Callback (line 153)
    TF = strncmpi(excelfile,datefile.ParticipantID,8);

When executing these commands in the command window, everything works. What is the cause of it not working in the GUI script?

Answer 1

[Adam]

How to share data among GUI callbacks

[Arashidus]

When i try to open this page, it states that the site does not exist. I think you mean this: https://uk.mathworks.com/help/matlab/creating_guis/share-data-among-callbacks.html#bt9p4t0 However, this does not help me since i don't understand how the GUI stores and retrieves data. Do you know any sources which could explain the basics of GUI and callbacks?

[Adam]

This link explains exactly that (I have corrected my link now, not sure what went wrong with it before). The whole page is concerned with storing and retrieving data within the callbacks of a GUI