uigetfile canceled returns 0, converting my string to a scalar

when I call [infile, location] = uigetfile() and it's canceled, it returns 0s, converting my strings to a scalars

Next time I call it I get an error:

Error using uigetputfile_helper/checkString

Filename must be a character vector or a string scalar.

How do I get my string back for infile to be properly used next time?

This shouldn't be that hard! I even tried converting the vars back to strings but it still fails after a cancel loop

function LoadfromTextFileButtonPushed(app, event)
%  Open the file in the Load trials text 
if  isempty(app.loc)
    [infile, app.loc] = uigetfile('*.txt','Select a Stimulus File',app.defLoc);
else 
    [infile, app.loc] = uigetfile('*.txt','Select a Stimulus File',app.loc);
end
if infile == 0 % user canceled
    app.FileName.Text  = 'Click Load From Text File or enter manually';
    % give me back a string var for next time
    infile = '';
    app.loc = app.defLoc; % return to default string
    return;
end
% Put full file name into the File field name and read it in
locfile = fullfile(app.loc,infile);
app.FileName.Text  = locfile;
app.UITable2.Data = readtable(locfile);
end

Answer 1

[Walter Roberson]

if isnumeric(infile)

instead of testing == 0

[Alessandro Livi]

Either works but the problem is getting infile back to a string for the next call.

[infile, app.loc] = uigetfile('*.txt','Select a Stimulus File',app.loc);

the second time around is what fails

The errors pointed out are in the helper files that I can't edit

Error using uigetputfile_helper/checkString

Filename must be a character vector or a string scalar.

[Alessandro Livi]

I've even tried this after the cancel:

% give me back a string var for next time

clear infile;

infile = '';

app.loc = app.defLoc; % return to default string

Command line shows infile = '' but still errors out

[Walter Roberson]

Don't assign to app.Loc until after you have verified infile

if  isempty(app.loc)
    [infile, apploc] = uigetfile('*.txt','Select a Stimulus File',app.defLoc);
else 
    [infile, apploc] = uigetfile('*.txt','Select a Stimulus File',app.loc);
end
if infile == 0 % user canceled
    app.FileName.Text  = 'Click Load From Text File or enter manually';
    % give me back a string var for next time
    app.loc = app.defLoc; % return to default string
    return;
end
app.loc = apploc;